LOCAL
DEMONSTRATIONS
Revised 2009
LOCAL DEMONSTRATIONS
TABLE OF CONTENTS
Topic 1. ATOMIC THEORY
1.1
Atomic Spectra (see also Demonstration 1.7)
1.2
Cathode Ray Tube
1.3
Flame Tests
A. For Small Groups
B. For Large Groups
1.4
The Relationship Between Energy and the Number of Nodes in a Standing Wave
1.5
Superconductivity
1.6
Electrostatic Forces
1.7
Gas Discharge Tube Colors
Topic 2. CHEMICAL BONDING
2.1
Singlet Molecular Oxygen (Not recommended for use in 1352, 1652, and 1810)
2.2
Paramagnetism of Liquid Oxygen
2.3
The SN2 Machine
Topic 3. COORDINATION CHEMISTRY
3.1
Iodo Complexes of Mercury(II), “The Orange Tornado”
3.2
Chloro Complexes of Cobalt(II)
3.4
Cis and Trans Isomers of [Co(en)2Cl2]Cl
3.5
Ethylenediamine Complexes of Nickel(II)
3.6
Amine Complexes of Copper(II), Cobalt(III), and Nickel(II)
Topic 4. ELECTROCHEMISTRY
4.1
The Daniell Cell
4.2
A Gravity Cell
4.3
A Citrus Cell
4.4
The Electrolysis of Water
4.4a
The Electrolysis of Water: H2 + O2 Climax
4.5
The Electrolysis of Aqueous Potassium Iodide
4.7
The Galvanic Cell with the Hydrogen Electrode
4.8
Alupowder – The Aluminum/Oxygen Cell (Discontinued)
4.9
The Voltaic Pile
Topic 5. EQUILIBRIUM
5.3
NO2/N2O4 Equilibrium
5.4
pH Demonstration (strong and weak acids, salts of strong and weak acid)
5.16
Simple Precipitation Reactions
5.17
Buffer Capacity
5.18
Hydrolysis of Salts
i
Table of Contents (continued)
Topic 6. GASES
6.1
Atmospheric Pressure, “How to Crush a Metal Can With No Hands”
6.2
Liquid Nitrogen Rocket (Not recommended for rooms 1352, 1652, and 1810)
6.3
The Ammonia Fountain (see also Demonstration 16.12)
6.4
Gas Phase Reactions
A. NH3(g) + HCl(g) → NH4Cl(s)
B. H2(g) + 1/2 O2(g) → H2O2(g) + bang; Hydrogen-Oxygen Pop Bottles and Balloons
C. H2(g) + Cl2(g) → 2 HCl + bang; The Hydrogen-Chlorine Cannon
(Not recommended for rooms 1652 and 1810)
6.8
The CO2 Bubbler
6.9
Shrinking a Balloon in Liquid Nitrogen (Charles' Law)
6.10
The Volume of a Mole of Gas
Topic 7. IONS, CONDUCTIVITY, and ELECTROLYSIS
7.2
Conductivity Changes in a Chemical Reaction, Ba(OH)2 + H2SO4
7.3
Conductivity of a Fused Salt
Topic 8. KINETIC MOLECULAR THEORY
8.1
Diffusion of Hydrogen
8.2
The Cryophorus
Topic 9. KINETICS
9.1
Iodine Clock Reaction
9.2
“William Tell Overture Clock”
9.3
“Old Nassau”
9.4
Red, White, and Blue Clock Reaction
9.5
Oscillating Clock Reactions I. The Bromate System
9.6
Oscillating Clock Reactions II. The Iodate System
9.7
Dust Explosion
A. The Grain Bin
B. The Flaming Pumpkin
9.8
Catalytic Decomposition of Hydrogen Peroxide
A. Inflate a Balloon
B. Genie in a Bottle
C. Decomposition of Hydrogen Peroxide Using Potassium Iodide
D. Elephant Toothpaste
9.9
Platinum Catalyzed Oxidation of Ammonia
9.10
Copper Catalyzed Oxidation of Methanol
9.11
Reaction Orders, Rate Laws, Visual Estimation of the Initial Rate of Reaction for
2 H+ + H2O2 + 3 I– → I3– + 2 H2O
9.12
Corning Catalytic Combustor Unit
9.13
The Formaldehyde Clock Reaction
9.15
The Rainbow Connection
ii
Table of Contents (continued)
Topic 10. LIQUIDS
10.1
The Vapor Pressure of Liquids (Discontinued)
10.2
Crystal Structure Diffraction
10.3
Differential Evaporation Rates
Topic 11. METALS AND METALLURGY
11.1
Reactions of the Alkali and Alkaline Earth Metals with Water
11.5
Sodium in Liquid Ammonia (Not recommended for rooms 1352, 1652, and 1810)
11.11
Hydrogen Reduction of Copper(II) Oxide, “The Copper Crystal”
(Not recommended for rooms 1352, 1652, and 1810)
11.12
The Oxidation States of Vanadium
11.13
The Hydrolysis of Titanium Tetrachloride, “Skywriting”
Topic 12. NON-METALS
12.3
The Halogen Train (Not recommended for rooms 1352, 1652, and 1810)
12.5
Sublimation of Iodine
12.14
Nitrogen Oxides and Nitric Acid
12.15
Preparation of Silane, SiH4
Topic 13. NUCLEAR CHEMISTRY
13.1
Radioactive Minerals
13.2
Chain Reaction Simulation
Topic 14. ORGANIC CHEMISTRY
14.1
Production of Ethylene by Dehydration of Ethanol
14.2
Production of Acetylene by the Reaction of Calcium Carbide with Water
A. Collection of Acetylene
B. Calcium Carbide Explosion
C. Calcium Carbide Sock Shooter (Not recommended for 1352, 1652, and 1810)
14.3
Bromination of Unsaturated Hydrocarbon Gases
14.4
The Methane Mamba (Not recommended for rooms 1352, 1652, and 1810)
Topic 15. POLYMER CHEMISTRY
15.6
The Gelation of a Poly(vinyl alcohol) with Borax, “Slime”
15.7
Disappearing Styrofoam
15.8
Happy and Sad Balls
Topic 16. REDOX CHEMISTRY
16.10
The Blue Bottle
16.13
Fireworks
iii
Table of Contents (continued)
Topic 17. SOLUTIONS AND SOLIDS
17.1
Unsaturated, Saturated and Supersaturated Sodium Acetate Solutions
17.3
Vapor Pressure Lowering, “Verification of Raoult’s Law” (Discontinued)
17.4
Osmotic Pressure
17.6
Radial Chromatography of Ink
17.7
The Bubble Raft
17.8
Liquid Nitrogen Ice Cream
17.9
The Re-Gelation of Ice
17.10
Solids: Sink or Float?
17.11
Crystal Samples
17.12
Chemical Color Change with Temperature
17.14
The Bubble Raft
Topic 18. STOICHIOMETRY
18.1
The Mole
Topic 19. THERMOCHEMISTRY
19.12
The Ethanol Cannon
Topic 20. PHYSICAL PROPERTIES
20.1
The Metric System: Volume, Length, and Weight
20.2
Density
A. Classic Coke vs. Diet Coke
B. Golf and Bowling Balls
20.3
Atmospheric Pressure
iv
TITLE:
TOPIC:
Atomic Spectra
Atomic Theory
DEMONSTRATION
(Kit)
1.1
Preparation
Equipment needed:
Gas discharge tubes (available tubes include hydrogen, helium, argon, neon,
and mercury), one power supply per discharge tube, one diffraction grating for
every 1-4 students.
Chemicals needed:
None.
The gas discharge tubes and power supplies are in Gilman 0732A. Diffraction gratings are in
Gilman 0162’s Tote Tray cabinet, 162-09.
Each gas discharge tube is mounted in the electrodes of a power supply. Have a supply of
diffraction gratings ready to pass out to the students.
Demonstration
Pass out the diffraction gratings, turn on the power supply, and view the tube through the diffraction
grating. Have the class also use the gratings to view the tube. You may need to describe what you
see in the grating in order to focus the students’ attention on the line spectrum.
NOTE: Each diffraction gating is in a cardboard slide mount. A black spot indicates the right edge
of the side held to the eye. The grating is held within an inch of the eye. When looking at a gas
discharge tube, the spectrum lines are displaced to the right of the discharge tube. The room lights
should be turned off to make the lines easier to see. Remember that the size of the image decreases
as the distance from the discharge tube increases. Students in the last rows may not see as much as
you would like them to see. If time permits, invite them to view the discharge tube up front after the
lecture is over.
After Class
Remind the students to return the diffraction gratings. If some boxes are placed near the doors, the
students can drop off the gratings on their way out. However, collecting the diffraction gratings
immediately after use minimizes the number lost.
1
TITLE:
TOPIC:
Cathode Ray Tube
Atomic Theory (Structure)
DEMONSTRATION
(Kit)
1.2
Preparation
Equipment provided: Cathode ray tube, magnet (horseshoe type), 2 wires (1 red, black)
Chemicals needed:
None required.
Equipment needed:
Power supply (rectangular box) with rheostat (cylinder) in Gilman 0162-9.
Connect the cathode ray tube to the terminals of the power supply. The bulldog clips fasten to the
ends of the cathode ray tube. The power supply’s polarity has never been determined.
The demonstration set-up. The picture at the right is an enlarged view of the white square.
Demonstration
The power supply lacks a switch. It is turned on by inserting the plug in an electric outlet.
Orient the cathode ray tube so that the white side of the metal faces the audience. Turn on the power
when ready to begin the demonstration. A green line becomes visible on the metal piece in the tube.
The magnet deflects the line, showing that the ray is composed of charged particles. Turn off the
power as soon as the demonstration is complete.
Safety
ELECTRICAL SHOCK HAZARD! The power supply produces 5000 volts of electricity. Do NOT
touch any part of the demonstration except the magnet while power is on. Do not touch any part of
the demonstration with the magnet except the cathode ray tube’s glass shell. Have the power on
only during the demonstration.
2
TITLE:
TOPIC:
Flame Tests for Small Groups
Atomic Theory
DEMONSTRATION
(Kit)
1.3A
Preparation
Equipment needed:
Bunsen or Meeker burner, flint striker.
Chemicals needed:
Kit of solutions for flame tests (includes wire and holder for making test).
Demonstration
Light the burner and insert the wire with the solution you wish to test into the burner flame. Colors
are best viewed with the room lights dimmed. This version of the Flame Tests demonstrations
works best for small groups which can come close to the bench.
Waste Disposal
None required.
3
TITLE:
TOPIC:
Flame Tests for Large Groups
Atomic Theory
DEMONSTRATION
(Kit)
1.3B
Preparation
Equipment needed:
Transite sheet (to protect bench surface from heat), five or six 100 mm
evaporating dishes, fire starter (or matches & applicator sticks),heat resistant
gloves, wooden snuffer.
Chemicals needed:
Methanol, lithium chloride, potassium chloride, sodium chloride, calcium
chloride, strontium chloride, copper chloride (if desired).
Put about 10 g of each salt in individual evaporating dishes.
Demonstration
Add methanol to each evaporating dish until the salt is covered. Ignite the methanol in each dish
with the fire starter or a burning applicator stick. The color of the burning salt is superimposed on
methanol’s faint blue flame. Colors are best viewed with the room lights dimmed. This version of
the Flame Tests demonstration is suitable for large lecture rooms because the flames are visible to a
considerable distance.
At the end of the demonstration, the flames can be snuffed by putting the piece of wood over the top
of a dish. Caution: sometimes the dishes get hot enough to reignite the methanol vapor.
Safety
Methanol is flammable. The burning methanol in the dishes is hot enough to burn human skin. The
evaporating dishes can get uncomfortably hot and should be handled with heat-resistant gloves.
Waste Disposal
All chemicals except the copper chloride and strontium chloride can be dissolved in water and
flushed down a sink. Strontium chloride and copper chloride are dissolved in water and packaged
for waste pickup by Environmental Health and Safety. A waste label is on the demonstration waste
web page.
Acknowledgement
Thanks to Dr. Dennis C. Johnson, ISU Chemistry Department
4
TITLE:
TOPIC:
The Relationship Between Energy and the Number
of Nodes in a Standing Wave
Atomic Theory
DEMONSTRATION
(Kit)
1.4
Preparation
Equipment provided: yellow chalk line, oscillator, ringstand clamps, four 3” C-clamps, aluminum rod
Equipment needed:
1 ringstand with heavy flat base (Gilman 0732)
2 heavy ringstand with tripod base (Gilman 0162)
1 variable speed mixer (with chuck) (Gilman 0732)
Two C-clamps fasten the base of each tripod ringstand securely to the ends of the lecture bench.
One ringstand clamp goes on each tripod ringstand, about 8 inches below the top. The yellow chalk
line is tied to the two clamps fairly tautly.
The mixer is clamped to the flat base ringstand, and the oscillator is fastened in the mixer’s chuck.
The mixer is positioned at one end of the chalk line so that, when turned on, the revolving oscillator
moves the string up and down. Aluminum rods hold the mixer ringstand to the tripod. (Photos on
the following pages)
If possible, the ringstands and other equipment should be set up and tested when the lecture hall is
vacant. Sometimes the equipment can be left in place until the lecture. If the equipment cannot be
left in place, tear down is confined to taking off the C-clamps and moving everything to the staging
area. Moving the equipment back to the lecture room, reinstalling the C-clamps, and replacing the
mixer are the only steps required to reset the demonstration.
Demonstration
Plug the mixer into a power socket and turn it on. Increasing the mixer speed increases the number
of nodes in the vibrating string, from two at a low speed to six or seven at maximum speed. The
chalk line is quite visible against the blackboard in Gilman 1002.
Clean Up and Waste Disposal
Disassemble the demonstration, and return the equipment to the original locations.
5
The Standing Wave Demonstration in Gilman 1002. The string is tied high on the two tripods.
The string is most visible at this height because of the contrast against the blackboard.
A closer view of the left third of the demonstration.
The vibrating string is a blur.
A clamp is on the tripod, and the string is tied to
the clamp with a clove hitch.
Electric mixer with oscillator. An aluminum rod
holds the mixer ringstand to the tripod.
Two C-clamps fasten a tripod to the corner
of the bench.
6
TITLE:
TOPIC:
Superconductivity
Atomic Theory
DEMONSTRATION
(Kit)
1.5
Preparation
Equipment provided: superconducting disk
small magnets
styrofoam cup
forceps
Equipment needed:
one liter Dewar flask (for liquid nitrogen) (Gilman 0732-B6)
Elmo unit or overhead projector (optional; for large groups)
Chemicals needed:
liquid nitrogen (Gilman 0732-A1)
Demonstration
Turn the styrofoam cup so that the base is up. Put the one inch superconducting disk on the cup, and
put the magnets on the disk. Pour a little liquid nitrogen on the cup base, and add more as needed.
A low ridge around the cup base retains the liquid nitrogen. When the superconductor is cold
enough, the magnets levitate.
See also the reference literature in the kit.
Note: The magnets are so tiny that they can only be seen from close by.
Clean Up and Waste Disposal
Scatter the excess liquid nitrogen on the ground outside the building.
Safety
Liquid nitrogen is extremely cold. Do not allow any to fall on bare skin, clothes, or shoes.
Reference
Institute for Chemical Education. Project 1-2-3 Levitation Kit. University of Wisconsin - Madison.
(In the demonstration kit.)
7
TITLE:
TOPIC:
Electrostatic Forces
Atomic Theory
DEMONSTRATION
(Kit)
1.6
Preparation
Equipment provided: Friction rod kit (rabbit fur exciting pad, silk exciting pad, wool felt exciting
pad, pith balls on threads, Lucite = Plexiglas rod, glass rod, hard rubber rod)
Equipment needed:
Ringstand, buret clamp, 50 mL buret
Chemicals needed:
Water (in buret)
Demonstration
The various rods are rubbed on the various exciting pads to generate static electricity. The rods
attract or repel the pith balls, depending on the charge. The series from most positive to most
negatively charged is rabbit fur, Lucite, glass, wool, silk, rubber. A charged rod also causes a stream
of water from a buret to bend rather than falling straight down.
References
Anonymous. Triboelectric effects. http://www.fas.harvard.edu/~scdiroff/lds/ElectricityMagnetism/
TriboelectricEffects/TriboelectricEffects.html
Kurtus, Ron. 2008. Materials that cause static electricity. http://www.school-for-champions.com/
science/static_materials.htm
8
TITLE:
TOPIC:
Gas Discharge Tube Colors
Atomic Theory
DEMONSTRATION
1.7
See Demonstration 1.1
This demonstration is Demonstration 1.1 without the diffraction gratings.
Preparation
Equipment needed:
Tripod ringstand with a cluster of argon, neon, helium, and nitrogen gas
discharge tubes (Gilman 0162 – metal shelf unit by sink)
Tesla coil (Gilman 0162)
Demonstration
Turn down the lights to let the colors be seen easily. Plug in the Tesla coil and dial up the knob at
the thick end until the coil can produce a good spark. Touch the tip of the Tesla coil to the bolt
sticking up from the cluster’s bottom surface. Touching the Tesla coil to any of the bolts through the
cluster’s top is almost as good. All four gas discharge tubes light up in different colors.
Safety
Do not touch the tip of the Tesla coil to human skin because the electric spark can cause a burn.
Hold the Tesla coil by the grip on the thick end to avoid a very disagreeable tingle.
9
TITLE:
TOPIC:
Singlet Molecular Oxygen
Chemical Bonding
DEMONSTRATION
2.1
Preparation
Equipment needed:
Gas washing apparatus (Kimble #31750), large Pyrex tray, 1 L filter flask
with stopper and glass tubing, rubber tubing, vinyl or rubber gloves, ringstand,
two 3-finger clamps.
Chemicals needed:
Lecture bottle of chlorine (with stand), 100-mL of 30% H2O2, 400-mL of
6 M NaOH.
Measure the H2O2 into a 100-mL graduate and cover with Parafilm. Pour 25 mL of the 6 M NaOH
into a small beaker. Pour about 300-400 mL of the 6 M NaOH into the filter flask. Connect the
outlet of the chlorine tank to the frit outlet of the gas washing bottle, using rubber tubing. Attach a
length of rubber tubing, long enough to reach the bottom of the filter flask, to the top outlet of the
gas washing apparatus. (See sketch below for details. The 3-finger clamp holding the filter flask to
the ringstand is not shown.)
Demonstration
Pour the H2O2 and the 25-mL of NaOH into the gas washing bottle. Replace the top and make
certain the outlet tubing from the top is in the NaOH bath in the filter flask. Turn on the chlorine gas
and increase the flow until a bright red emission is observed about 1-2 cm above the frit. The room
lights should be dimmed to allow the students to see. In a matter of minutes the catalytic
decomposition of H2O2 becomes vigorous, and the entire mixture may boil over, hence the glass tray.
After observing the glow, it is best to disconnect the apparatus and put it in a hood until it can be
cleaned. Clean the apparatus and dispose of the waste as soon as possible.
Clean Up and Waste Disposal
Pour the H2O2 solution into a beaker and use a little FeCl3 solution to decompose the remaining
H2O2. Neutralize the base with acid. Work in a hood because chlorine gas is liberated. Flush the
neutralized solutions down a sink. Connect the gas washing apparatus to an aspirator and run
several changes of distilled water through it to rinse it clean.
Reference
Shakhashiri, B. Z., “Chemical Demonstrations”, University of Wisconsin Press, Madison, WI,
Volume 1, Experiment 2.1, pages 133-145.
10
TITLE:
TOPIC:
Paramagnetism of Liquid Oxygen
Chemical Bonding
DEMONSTRATION
(Partial Kit)
2.2
Preparation
Equipment provided: Strong magnet
Equipment needed:
3 small glass dewars clamped to a white wooden stand (Gilman 0732-B1)
2 L dewar (Gilman 0732-B6), 2-4 feet of rubber tubing,
Boileezers, coil of copper tubing (Gilman 0609)
Chemicals needed:
4 L liquid nitrogen (in 10 L dewar in Gilman 0732-A1)
Tank of oxygen gas with regulator (Gilman 0732)
Optional:
cigarettes, crucible tongs, demonstration test tube, Pyrex pie plate, second
ringstand with three-finger clamp, heavy gloves
Approximately 20-30 minutes before the lecture begins, connect the oxygen tank to the copper coil
with a length of rubber tubing. Let oxygen flow through the coil for five minutes to evaporate any
moisture inside the coil. Fill a 2 L dewar flask 3/4 full from the 10 L dewar of liquid N2 and
immerse the copper coil in the 2 L dewar of liquid nitrogen. Top off the 2 L dewar with liquid
nitrogen when the vigorous boiling subsides to a moderate boiling. Secure a small glass dewar in a
three-finger clamp and wait for the liquid oxygen to begin to come out of the coil. Allow the first bit
to run out on the floor to minimize the amount of water ice collected. Fill two small glass dewars
with liquid oxygen. Fill the third glass dewar with liquid nitrogen from the 2 L dewar. Put a few
boileezers in each glass dewar to avoid burping, and put a plexiglas cap on each glass dewar.
Demonstration
Pour some liquid nitrogen over the magnet faces. The nitrogen runs off, showing that nitrogen is not
paramagnetic. This also cools the magnet. Next, pour the liquid oxygen from a small dewar. The
oxygen should be poured down one face of the magnet to allow the oxygen to form a bridge between
the magnetic poles. If the oxygen is poured into the gap between the faces, it will probably fall
through the magnet too quickly to be caught in the magnetic field.
Note: The clear glass dewars allow the class to observe the blue color of the liquid oxygen. The
stand’s white background is helpful if you wish to have the students note the color. The absence of
color in the liquid nitrogen can also be observed.
11
Paramagnetism of Liquid Oxygen (continued)
Clean Up and Waste Disposal
Empty the small dewars of liquid oxygen and liquid nitrogen on the ground in the courtyard. Turn
the dewars upside down to dry.
Safety
Oxygen is a strong oxidizer. Materials ignite more easily and burn faster in oxygen than in air.
Wear a plastic apron when making liquid oxygen because a spill of liquid nitrogen or liquid oxygen
concentrates oxygen in the weave of clothing. Liquid oxygen and liquid nitrogen are also very cold
and may damage skin if trapped in the weave of clothing. Keep the copper condenser in a locked
drawer in Gilman 0609.
Danger: Burning something in liquid O2 can crack a dewar. If burning something, do it in a heavywalled test tube or 200 mL Berzelius beaker, not a dewar. A large crystallizing dish containing a
layer of sand catches any spills or broken glass.
Reference
Shakhashiri, B. Z., “Chemical Demonstrations”, University of Wisconsin Press, Madison, WI,
Volume 2, Experiment 6.10, pages 147-152.
12
TITLE:
TOPIC:
The SN2 Machine
Chemical Bonding
DEMONSTRATION
2.3
Preparation
Equipment needed:
SN2 machine (Gilman 0162, top of a shelf unit)
Demonstration
Left: A free ion (solid-colored ball on the bar’s left) attacks a carbon atom (center of bar).
Center: The attacking ion and the organic molecule form an activated complex.
Right: The attacking ion binds to the carbon atom and displaces the ion (striped ball) on the opposite
side of the carbon atom. The displacement reaction inverts the geometric arrangement of the other
groups attached to the carbon atom.
13
TITLE:
TOPIC:
Orange Tornado
Coordination Chemistry
DEMONSTRATION
3.1
Preparation
Equipment needed:
magnetic stirrer, 2” magnetic stirring bar, 4 L beaker, 2-50 ml buret, 2 ring
stands, 2 double buret clamps, slide projector (Chemistry Stores Office),
wooden box (to raise the slide projector to the beaker’s level), cardboard
slides with various size holes (Gilman 0162)
Chemicals needed:
1 M KI, 0.1 M HgNO3
Place a 4-liter beaker containing 3500 mL of distilled water and the stirring bar on the magnetic
stirrer in front of a black backdrop. The blackboard will do. Adjust the stirring rate to form a
smooth, nonturbulent vortex extending approximately 2 cm below the water’s surface. If desired,
adjust lighting from the side to light the column of liquid above the stirring bar without shining in
the eyes of the observers. A small high-intensity desk lamp or slide projector is satisfactory.
Add 35 mL of 0.10 M mercuric nitrate solution and allow a couple of minutes for complete mixing.
Demonstration
To perform the demonstration, add approximately 1 mL of 1.0 M potassium iodide solution by
injecting it vertically into the vortex using either a medicine dropper or a buret. Allow time for
observation. When the solution is once more clear and colorless, add a second increment of KI
solution. One mL increments provide a very satisfactory result through the addition of 4-5 mL, by
which time the precipitate of mercury(II) iodide, HgI2, no longer dissolves and each addition of KI
solution increases the amount of precipitate. To enhance mixing, inject subsequent additions of KI
solution down the side of the beaker instead of into the vortex.
The HgI2 precipitate dissolves after the addition of about 20 mL of KI solution, but the texture and
color of the precipitate undergo almost continuous change throughout the process, so many small
additions should be made instead of one large one. Shortly after the precipitate becomes generally
dispersed, it takes on the color of orange ice cream and has a silky texture reminiscent of the
mercurous chloride precipitate in the Zimmerman-Reinhardt determination of iron. As KI solution is
added, the color becomes increasingly red and is frequently caught in the surface tension in the
vortex.
When all the mercuric iodide has dissolved, add 2-3 more mL of KI solution to establish some
excess iodide ions in solution. Then add to the vortex some mercuric nitrate solution. One mL of
Mg(NO3)2 solution creates a satisfactory tornado of HgI2. However, 3-5 mL produce a more
impressive tornado, which lasts long enough for some of the color changes previously observed to
take place. Frequently, the last solid to disappear is red and is visible as a flickering ghost of the
tornado for a minute or more.
14
Orange Tornado (continued)
Slowing the rotation of the stirrer before adding mercuric nitrate solution allows greater freedom of
motion to the added ions and frequently creates some beautiful effects. Experimentation is
rewarding.
Eventually, the addition of mercuric nitrate solution produces a permanent precipitate, which
obscures the tornado. Addition of KI solution down the side of the beaker redissolves the mercuric
iodide and sometimes generates another tornado.
Alternate additions of mercuric nitrate and potassium iodide permit the phenomenon to be observed
repeatedly.
The demonstration needs no special termination to make it satisfying. However, a black tornado can
be generated by pouring very dilute sulfide ion solution into the vortex. The addition of stannous
chloride solution forms mercurous iodide but does not produce a good “tornado.” probably because
the reduction is not fast enough. Either of these procedures illustrates useful chemistry and helps
prepare the mercury solution for disposal.
Waste Disposal
Package the solution for Environmental Health & Safety waste pick up. The Demonstration Waste
web page has a waste manifest and label.
Reference
Shakhashiri, B. Z. “Chemical Demonstrations”, University of Wisconsin Press, Madison, WI,
Volume 1, Experiment 4.1, Procedure A, page 272.
15
TITLE:
TOPIC:
Chloro Complexes of Cobalt(II)
Coordination Chemistry
DEMONSTRATION
3.2
Preparation
Chemicals needed:
Cobalt(II) chloride (CoCl2), 95% ethanol, water, 12 M HCl
Materials needed:
250 mL beaker, 1” stirring bar, large demonstration test tube with test tube
rack, Parafilm, drip-top plastic bottles (30-60 ml capacity).
Dissolve 10 g of CoCl2 in one liter of either 95% ethanol or 2-propanol. If a more concentrated
solution is wished, add CoCl2 to the solution until the saturation point is reached. (This simple
method of preparing the CoCl2 solution is courtesy of Dr. Thomas Greenbowe.)
Demonstration
Place 25-50 ml of the CoCl2 solution in the large test tube. Dispense water and 12 M HCl from the
two drip-top plastic bottles. Using a 25 mL aliquot of the CoCl2 solution,
1 mL H2O → pink
1 mL 12 M HCl → blue
2 mL H2O → pink
2 mL 12 M HCl → blue
1 mL H2O → pink
2 mL 12 M HCl → blue
The CoCl2 solution can change color several times.
Clean Up and Waste Disposal
Bottle the used cobalt chloride solution and send it to Environmental Health and Safety. See the
Demonstration Waste web site for a waste manifest.
Reference
Shakhashiri, B.Z., “Chemical Demonstrations”, University of Wisconsin Press, Madison, WI,
Volume 1, Experiment 4.2, pages 280-285.
16
TITLE:
TOPIC:
cis and trans –[Co(en)2Cl2]Cl
Coordination Chemistry
DEMONSTRATION
(Kit)
3.4
Preparation
Equipment needed:
Display vials of the two isomers, white background.
Demonstration
The vials containing these two isomers are displayed with a white background. The trans isomer is a
bright green color while the cis isomer is a bright purple color.
These two compounds used to be prepared by students in the Chem 178L course. They measured
the rate of isomerization of the cis to the trans isomer in methanol using a spectrophotometer.
Note: Only small amounts of the two isomers are on hand. This demo may be most suitable
displayed with an Elmo unit (or other video camera/projector).
Clean Up and Waste Disposal
None.
17
TITLE:
TOPIC:
Ethylenediamine Complexes of Nickel(II)
Coordination Chemistry
DEMONSTRATION
3.5
Preparation
Chemicals needed:
200 mL 0.1 M Ni2+ solution [NiSO4, Ni(NO3)2, NiCl2], 15 mL 10%
ethylenediamine in H2O (vol/vol)
Materials needed:
Four large test tubes; white wooden test tube rack, one 10 mL graduated
cylinder, one 100 mL graduated cylinder
Put 50 mL of 0.1 M Ni2+ solution in each of the four test tubes.
Demonstration
No ethylenediamine is added to the first tube; it is the standard against which the other tubes are
compared. The second tube gets 2 mL of 10% ethylenediamine, the third tube gets 4 mL of 10%
ethylenediamine, and the fourth tube gets 8 mL of 10% ethylenediamine. Each tube turns a different
color as in the table below.
Tube
1
2
3
4
0.1 M Ni2+
50 mL
50 mL
50 mL
50 mL
10% ethylenediamine
0 mL
2 mL
4 mL
8 mL
Color
green
pale blue-green
blue
violet
Complex ion
--Ni(H2O)4(en)2+
Ni(H2O)2(en)22+
Ni(en)32+
Clean Up and Waste Disposal
Combine the solutions, and package the result for chemical waste pickup. See the Demonstration
Waste web page for a waste label and manifest.
Reference
Derived from Gillespie, Ronald J., David A. Humphreys, N. Colin Baird, Edward A. Robinson.
Chemistry. Allyn and Bacon, Inc., Boston. 1986. Experiment 21.11, p. 768.
18
TITLE:
TOPIC:
Amine Complexes of Cu(II), Co(III), and Ni(II)
Coordination Chemistry
DEMONSTRATION
3.6
Preparation
Equipment needed:
3 demonstration size test tubes
White wooden test tube rack
Chemicals needed:
50-100 mL 0.1 M Cu2+ (CuCl2, Cu(NO3)2, or CuSO4)
50-100 mL 0.1 M Ni2+ (NiCl2, Ni(NO3)2, or NiSO4)
6 M NH4OH
50 mL 0.02 M Co2+ (CoCl2, Co(NO3)2, or CoSO4)
10 mL 1% H2O2
Distilled water
Demonstration
Pour the Cu2+ solution into one test tube. Add 6 M NH4OH to the test tube. The blue solution
changes color to a much darker blue.
Cu2+ (light blue) + NH4OH → Cu(NH3)42+
(dark blue)
Pour the Ni2+ solution into a second test tube. Add 6 M NH4OH to the test tube. The green solution
turns violet.
Ni2+ (green) + NH4OH → Ni(NH3)62+
(violet)
Pour the pink solution of Co2+ into a third test tube. Add the H2O2 to oxidize the Co2+ to Co3+. Add
NH4OH to produce the deep red amine complex. Dilute the solution to the top of the test tube with
distilled water to show how intense the color is.
Co2+ (pale pink) + H2O2 → Co3+ + NH4OH → Co(NH3)63+ (deep red)
Clean Up and Waste Disposal
The three solutions can be combined and packaged for waste pickup by Environmental Health and
Safety. See the Demonstration Waste web site for a label and manifest.
Reference
Gillespie, Ronald J., David A. Humphreys, N. Colin Baird, Edward A. Robinson. Chemistry.
Allyn and Bacon, Inc., Boston. 1986. Experiment 21.10, p. 766.
19
TITLE:
TOPIC:
Daniell Cell
Electrochemistry
DEMONSTRATION
(Kit)
4.1
Preparation
Equipment provided: 2 500 mL Berzelius beakers, agar salt bridge, sandpaper or fine steel wool (for
polishing metal strips)
Chemicals provided: 400 mL 1 M CuSO4, 400 mL 1 M ZnSO4, copper strip, zinc strip
Equipment needed:
voltmeter (0732A)
1-red connecting wire (0732A) at least 3 feet long
1-black connecting wire (0732A) at least 3 feet long
Elmo TV Camera (Gilman 0162 or Gilman 1358)
CHECK TO BE SURE THE BATTERY IN THE VOLTMETER HAS ADEQUATE POWER.
Pour 400 mL of the CuSO4 into one beaker and a like amount of ZnSO4 into the other beaker. Put
the copper electrode in the CuSO4 and the zinc electrode in the ZnSO4. Connect the two electrodes
to the voltmeter leads with the red lead to copper. Insert the salt bridge. Turn on the voltmeter and
read the voltage. It should read between 1.05 and 1.15 V.
Disconnect the electrodes, remove the salt bridge, and turn off the voltmeter. Store the salt bridge in
1 M KNO3 solution. If the experiment is not to be done for some time, cover the beakers with
Parafilm until just before class.
Demonstration
Connect the voltmeter leads to the electrodes, connect the two solutions with the salt bridge, turn on
the voltmeter, and read the cell voltage on the voltmeter.
The voltmeter and Elmo TV camera can be set up so that the lecturer can see the voltmeter readout
and the class sees the readout projected on the screen.
Clean Up and Waste Disposal
The zinc and copper solutions are only used for this experiment. They may be poured back into their
respective bottles for reuse. The salt bridge is rinsed off and stored in a one liter beaker in around
250 mL of 1 M KNO3. The beaker is covered with Saran Wrap to prevent evaporation. The salt
bridges are good for two years or more when stored like this.
20
TITLE:
TOPIC:
Gravity Cell
Electrochemistry
DEMONSTRATION
4.2
Preparation
Equipment needed:
1 1-liter Berzelius beaker, long-stem funnel, voltmeter, connecting wires.
Chemicals needed:
300 mL saturated (> 1.0 M) CuSO4, 300 mL 0.1 M ZnSO4, zinc strip bent into
an L so it just reaches halfway into the beaker, copper strip bent into an L so it
reaches the bottom of the beaker.
Set up the voltmeter and check it out as in Demonstration 4.1.
Demonstration
Place the copper and zinc electrodes in the beaker. Pour the ZnSO4 solution into the beaker. Put the
long-stem funnel in the beaker so that the tip is at the very bottom when the beaker is tipped. Add
the CuSO4 solution slowly through the long-stem funnel so that the CuSO4 forms a distinct layer at
the bottom of the beaker and covers the bottom of the copper electrode. The zinc electrode should
be in the ZnSO4 layer but not touch the CuSO4 layer or the copper strip. Connect the voltmeter leads
to the electrodes as in Demonstration 4.1 and turn on the voltmeter. Read the potential of the cell.
Use the Elmo video camera as in Demonstration 4.1 so that the students can easily read the
voltmeter.
The solutions remain separated for over 15 minutes due to the difference in their densities. The
interface between the two solutions serves as the “salt bridge” as ions can move freely from one
solution to the other.
Clean Up and Waste Disposal
As the zinc and copper solutions slowly mix in this demonstration, they are combined in a waste
bottle for Environmental Health and Safety to pick up. See the Demonstration Waste web page for a
label and manifest.
Reference
Shakhashiri, B. Z., “Chemical Demonstrations”, University of Wisconsin Press, Madison, WI,
Volume 4, Experiment 11.6, pages 119-122.
21
TITLE:
TOPIC:
Citrus Cell
Electrochemistry
DEMONSTRATION
4.3
Preparation
Equipment needed:
Voltmeter, digital display, knife, connecting wires.
Chemicals needed:
Copper strip, zinc strip, lemon (or other piece of fresh citrus fruit).
Set up the digital display and voltmeter and check them out as in demonstration 4.1.
Demonstration
Cut two small slits in the lemon (or other piece of citrus). Insert the zinc and copper strips into these
two slits. Connect the strips to the voltmeter leads and read the cell potential. (This is truly a
Voltaic cell.)
Note: This has never been a satisfactory demonstration. Reducing the distance between the
electrodes and increasing the amount of cell wall breakage inside the citrus fruit may produce a
better result. Injecting CuSO4 and ZnSO4 around the respective electrodes may also help.
Clean Up and Waste Disposal
Discard the citrus fruit in the dumpster.
22
TITLE:
TOPIC:
The Electrolysis of Water: An Improved
Demonstration Procedure
Written by Steve Heideman
Electrochemistry
DEMONSTRATION
(Kit)
4.4
The usual demonstration of the electrolysis of water (using 0.5 M H2SO4) focuses the student’s
attention on the evolution of the gases hydrogen and oxygen. The accompanying pH changes at the
electrodes are unobserved and the writing of the equations for the reactions which occur at each
electrode may be skipped entirely to get to the equation for the net cell reaction.
2 H2O(l) → 2 H2(g) + O2(g)
The procedure described here uses a modified Hoffman electrolysis unit designed to keep the
products of the reaction separated. (See figure.) The electrolytic bath is a 1 M Na2SO4 solution to
which bromocresol green indicator has been added. The pH of the solution is initially near 4.5, the
approximate pKa of this indicator. The green color of the indicator in this solution results from the
presence of nearly equimolar quantities of the yellow acid-form and the blue basic-form of the
indicator. As the electrolysis proceeds, the color of the indicator changes at each electrode as the pH
of the solution near the electrode changes.
Equipment needed
12 volt DC power supply (0732A)
modified Hoffman electrolysis unit (see figure) (0162)
1-4’ red connecting wire (0162)
1-4’ black connecting wire (0162)
1 funnel (0732-A9)
Equipment provided
4 300 mL beaker
4 stirring rods
Reagents provided
1 L of 1 M Na2SO4, with bromcresol green indicator, pH 4.5
1 M H2SO4
1 M NaOH
Demonstration
Add 20 mL of the bromocresol green indicator to 400 mL of 1 M Na2SO4. Adjust the pH of the
solution to approximately pH 4.5 by adding the 1 M CH3COOH dropwise while stirring. The
solution will have a clear, green color at this pH. Fill the electrolysis unit with the solution and
divide the remaining solution equally between two beakers. Connect the DC power supply and start
the electrolysis. The experiment should run for several minutes to produce sufficient volumes of the
gases to be easily seen by the students and to allow the indicator to change color. The electrolysis
unit is designed to shut off as the hydrogen forces the solution out of contact with the cathode, thus
the experiment is not ruined if you forget about it while lecturing
23
The Electrolysis of Water: An Improved Demonstration Procedure (continued)
Observations
At the anode: The solution has turned light yellow in color and one unit volume of gas is present
above it. If the gas is collected and a glowing splint thrust into it, the splint bursts into flame. Add
some 1 M H2SO4 to one of the beakers containing the indicator. The solution turns yellow indicating
the solution at the anode is acidic.
At the cathode: The solution is a deep blue color with two unit volumes of gas present above it. If
the gas is collected and brought near a flame a “pop” is heard. Add some 1 M NaOH to the second
beaker of indicator and observe the color change from green to blue. The solution around the
cathode is basic.
Drain the solution from the electrolysis unit into a 600-mL beaker. Observe the change in color
from yellow near the anode and blue near the cathode to green in the beaker. The solution is now
the same color as it was initially.
Conclusions
Anode: Oxygen gas and hydronium ions are produced at this electrode.
Cathode: Hydrogen gas and hydroxide ions are produced at this electrode.
Recall for the students that equal volumes of gas contain equal number of moles of gas; therefore,
two moles of hydrogen gas are produced at the cathode for each mole of oxygen gas produced at the
anode.
The acid and base produced at the anode and cathode, respectively, just neutralize each other.
From these observations and conclusions the following reactions may be written.
At the anode:
6 H2O(l) → 4 H3O+(aq) + O2(g) + 4 e–
At the cathode:
4 H2O(l) + 4 e– → 4 OH– + 2 H2(g)
Net cell reaction:
2 H2O(l) → 2 H2(g) + O2(g)
The observations made in this demonstration lead directly to the writing of the appropriate equations
for the reactions at each electrode. The combination of these two electrode reactions yields the net
cell reaction while giving the student a more complete explanation of the chemical reactions
involved in the electrolysis of water.
Clean Up and Waste Disposal
Dispose of the acidic and basic solutions by neutralizing them and flushing them down a drain. The
Na2SO4 solution from the electrolysis unit can be returned to the bottle for reuse. Flush the
electrolysis unit several times with distilled water, fill it with distilled water, and cap the bulb at the
top to prevent evaporation.
24
TITLE:
TOPIC:
The Electrolysis of Water: H2 + O2 Climax
Electrochemistry
DEMONSTRATION
(Kit)
4.4a
Preparation
Equipment needed:
#6 one-hole rubber stopper, plastic freezer bag (8 x 4 x 2 inch, 1 pint
capacity), 9-10 inches of 16 gauge copper wire, student ringstand, pliers and
wire cutter, candle on a stick, fire starter (or matches)
Chemicals needed:
hydrogen gas, oxygen gas (generated by electrolysis)
Put the rubber stopper inside the freezer bag about 2 inches in from the open end.
Loop the wire around the stopper twice, pull the wire tight, and twist it to seal the bag
to the stopper. Curl the wire ends back to prevent scratches. Cut the open end of the
bag back to the stopper.
Demonstration
Collecting and exploding the hydrogen and oxygen from the electrolysis
demonstration is optional but provides a nice climax to the demonstration. This is a
small version of Demonstration 6.4B. A decent pop requires running the electrolysis apparatus until
the hydrogen level drops below the electrode in that arm. That is the failsafe point, when the current
can no longer flow.
When ready to collect the gases, the lecturer turns off the electrolysis apparatus’ power. This MUST
be done first! After air is squeezed out of the plastic bag, the rubber stopper is placed on the outlet to
the oxygen side of the electrolysis apparatus. The stopcock is opened, and the displaced Na2SO4
solution forces the oxygen into the plastic bag. Close the stopcock when the solution is within an
inch of the stopcock. Lift the rubber stopper off the oxygen outlet and plug the hole in the stopper
with a fingertip. Collect the hydrogen in the same way as the oxygen, which produces a nearly
stoichiometric mixture of H2 and O2 in the bag. Jam the stopper on the tip of the student ringstand.
This plugs the hole in the stopper, preventing the gases from escaping. It also puts the bag high
enough for everyone to see it easily. Light the candle on the stick, stand back, and touch the flame to
the plastic bag. The “pop” is not as loud as a hydrogen-oxygen pop bottle, but it is easily audible at
the back of Gilman 1002.
Clean Up
After it cools, the exploded bag and wire go in a waste basket. All of the other equipment is returned
to the original locations.
Safety
See Demonstration 6.4B.
25
TITLE:
TOPIC:
The Electrolysis of Aqueous Potassium Iodide
Electrochemistry
DEMONSTRATION
4.5
Preparation
Equipment needed:
Power supply (0732A)
two platinum electrodes, one with a wire about three inches long and the other
with a six inch long wire (0732-G2).
large U-tube (approximately 12 inches high, 9 inches wide, and 1 inch thick)
two #5 rubber stoppers
one red wire and one black wire each about 3 feet long with a banana plug at
one end and an alligator clip at the other
one ring stand
one three-finger clamp
white background (optional).
Chemicals needed:
400 mL of 0.5 M potassium iodide solution
phenolphalein.
The three-finger clamp is attached to the ringstand. The U-tube is put in the three-finger clamp, with
the open ends up. A squirt of phenolphthalein is mixed into the potassium iodide solution, which
should remain clear instead of turning pink. This solution is used to fill the U-tube to about 3/4 inch
from the top. A platinum electrode is placed in each open end with the end of the wire hooked over
the edge. A #5 solid rubber stopper closes each open end to minimize spillage during transport.
The wire from the positive (red) outlet of the power supply is clipped to the short electrode. The
wire from the negative (black) outlet of the power supply is clipped to the long electrode.
Demonstration
Remove the stoppers. Turn on the power supply. Brown iodine drifts downward from the positive
electrode. Potassium hydroxide drifts upward from the negative electrode causing the
phenolphthalein to turn pink.
Clean Up and Waste Disposal
Dump the solution into a beaker. Add sodium thiosulfate to oxidize the iodine, then neutralize the
base. Discard the neutralized solution down a sink.
Reference
Alyea, Hubert N., and Frederic B. Dutton. Tested Demonstrations in Chemistry.
1965, 231 pp. See p. 12, demo 4.18.
26
TITLE:
TOPIC:
The Galvanic Cell With the Hydrogen Electrode
Electrochemistry
DEMONSTRATION 4.7
(Kit – Demonstration 4.1)
Purpose
To demonstrate voltaic or galvanic cells, to demonstrate the standard hydrogen electrode, to
determine relative half-cell potentials, to verify the additivity of half-cell potentials, to demonstrate
the function of a salt bridge, and to introduce concentration cells.
Preparation
Equipment needed:
An Elmo unit
electrochemical cell template (of plexiglas)
3 crystallizing dishes (0732-A8)
hydrogen electrode
voltmeter
1 black connecting wire
1 red connecting wire
U-tube salt bridge
six-inch lengths of zinc and copper metal
steel wool for polishing the metal (0732A, tote-tray cabinet)
Chemicals needed:
1.0 M solutions of Zn2+ and Cu2+
1.0 M HCl
hydrogen gas cylinder with valve and 18” rubber tube
saturated solution of KCl to fill the salt bridge
The electrochemical cell template is placed on top of the Elmo unit and connected to a voltmeter.
The metal samples used in this demonstration should be polished with steel wool. The three
crystallizing dishes are filled respectively with 1.0 M CuSO4, 1.0 M ZnSO4, and 1.0 M HCl.
Demonstration
Place the dishes holding ZnSO4 and HCl in the appropriate holes in the electrochemistry template.
Bend a strip of Zn metal, attach one end of the metal strip to one of the posts of the electrochemistry
template and place the other end into the crystallizing dish filled with 1.0 M Zn2+ solution. Connect
the hydrogen electrode to the other post, place the Pt wire in the HCl solution, connect the electrode
to a gas cylinder, and bubble H2 gas through the solution (see Figure A). Note the potential in the
absence of a salt bridge (0.00 V), then insert the U-tube salt bridge into the two crystallizing dishes
and measure the potential difference. Typical values obtained using this apparatus are 0.76 ±
0.06 V. If the leads are connected so as to produce a potential of +0.76 V, the cell is a voltaic or
galvanic cell. The Zn2+/Zn half-cell is the anode, and the H+/H2 half-cell is the cathode.
Replace the Zn2+/Zn half-cell with a Cu2+/Cu half-cell. Reinsert the salt bridge and record the
potential difference. Note that both the magnitude and the sign of the potential change. If the leads
were connected to produce a potential of +0.76 V in the first cell, the potential for this cell should be
roughly –0.34 V.
27
Replace the H+/H2 half-cell with the Zn2+/Zn half-cell (see Figure B). Reinsert the salt bridge and
record the potential. The cell potential should be –1.10 V. If the leads are changed, the cell
potential becomes +1.10 V, and the cell becomes a galvanic or voltaic cell.
Remove the salt bridge and note that the cell potential immediately falls to zero. Stick one finger
into one crystallizing dish and another finger into the other dish. Note that the potential returns to
almost 1.10 V. Place a finger from one hand in one dish and a finger from the other hand in the
other dish. Once again the potential returns to almost 1.10 V. Call for a volunteer from the
audience, link hands, place one finger in one dish, and ask the student to place one finger in the other
dish. Once again the potential returns to 1.10 V.
Replace the Zn2+/Zn half-cell with a Cu2+ (0.0100 M)/Cu half-cell. Reinsert the salt-bridge and
record the potential. Discuss the concept of concentration cells.
Clean Up and Waste Disposal
Neutralize the acid, and flush it down a sink. Wash and store the metal electrodes. Store the
hydrogen electrode in 1 M HCl. Either dispose of the metal sulfate solutions in the proper waste
bottles or save them for reuse in this demonstration.
Reference
Bodner, Keyes, and Greenbowe, “The Purdue University Lecture Demonstration Manual”,
demonstration 19.4.
28
TITLE:
TOPIC:
Alupower – The Aluminum/Oxygen Cell
Electrochemistry
DEMONSTRATION
(Discontinued)
4.8
Discontinued due to corrosion in the demonstration battery and lack of interest from lecturers.
Equipment provided: Aluminum-air demonstration battery
Chemicals provided: Sodium chloride solution (100 g/L)
This battery consists of two cells in series. Each cell contains an aluminum anode separated by a
narrow gap from an external air permeable cathode. The anode has open channels cut into it to
allow electrolyte circulation. When filled with 10-20% salt water solution, the pair of cells operating
the bulb (300 ma at about 2 volts) for a total of 20 to 40 hours. The purpose of changing the
electrolyte is to remove the aluminum hydroxide which is formed as a result of the electrochemical
reaction of the aluminum with oxygen from air.
Operation
To operate, place two heaping teaspoons of salt in a cup of water, (100 g/L), stir until the salt is
dissolved, and fill each of the cells to about 1/4” from the top. The light will take a few minutes to
come up to full brightness.
After operation (but not more than 4 hours) rinse several times with vigorous shaking. If the slots in
the aluminum plates are clogged, clear with a blunt object. Rinse until the bulb does not glow.
For immediate re-use, fill as described. If not, dry in air before storing. The cell may be used
several times until the aluminum is consumed.
Avoid damage to the air cathode. If punctured it will leak and cause the battery to malfunction.
Caution
During operation the liquid may become slightly acidic or alkaline. In case of contact with skin or
eyes, flush with water. If irritation occurs, consult physician.
Do not operate in a confined unventilated space, since a small amount of hydrogen is emitted during
operation.
The following comments pertain to the charts in the packet:
1.
General Concept – Emphasizes the fact that presentation is about a new type of battery
system based on aluminum as an electrochemical fuel.
2.
Electrochemical Comparisons – Points out high electrochemical equivalent of aluminum and
good theoretical voltage leading to a high theoretical specific energy for aluminum as a fuel.
Note that lithium batteries are hard to control in aqueous electrolytes.
29
Alupower – The Aluminum/Oxygen Cell (continued)
3.
Key Advantages – Emphasizes long shelf-life, low weight before use, and innocuous salt
water electrolyte. Much higher power levels can be reached using caustic sodium or
potassium hydroxide, but with greater generation of hydrogen and the inherent dangers of
using caustic electrolytes.
4.
Chemical Reactions – Describes three main components – aluminum anode, air cathode, and
salt water electrolyte. The reaction product is aluminum hydroxide, the basic ingredient of
toothpaste, which will eventually fill up the electrolyte space if the battery is run long
enough. Periodic rinsing will prevent this and allow all of the aluminum to be used.
5.
Air Cathode – Describes the workings of the air cathode. Oxygen from air diffuses through
the non-wetting layer and reacts with water on the conductive catalytic surface in the inner
layer of the electrode. This consumes electrons which flow from the circuit and forms
hydroxyl ions which enter the electrolyte and react with aluminum ions to form aluminum
hydroxide.
6.
Comparison with D-Cells – Compares the discharge of an aluminum-air cube cell with 2 DCells at a relatively high discharge rate. Shows that the voltage of the aluminum-air battery
is relatively constant with time, and that the capacity is quite high even when the electrolyte
is not changed. If the electrolyte is changed every four hours the capacity will be much
higher.
7.
Potential Applications – Gives some of the places where the aluminum-air battery concept
might be used in products.
30
TITLE:
TOPIC:
The Voltaic Pile
Electrochemistry
DEMONSTRATION
4.9
31
The Voltaic Pile (continued)
32
TITLE:
TOPIC:
NO2/N2O4 Equilibrium
Equilibrium
DEMONSTRATION
(Kit)
5.3
Preparation
Equipment provided: 2 1-L beakers, small ice chest
Chemicals provided: 2 sealed tubes of NO2(g)
Equipment needed:
White test tube rack (0162) or white background
2 Ringstand (0732)
2 3-finger clamp (0732-B3)
Heat gun (0162) or hot plate
Protective gloves
Chemicals needed:
Water ice (Gilman 0732) or dry ice or liquid nitrogen
(Please specify which is preferred.)
Clamp each sealed tube to a ringstand. This allows nearly total immersion in the beakers of water.
If left free, the tubes float and could fall on the bench and break.
Demonstration
Examine the color of the two tubes of NO2(g) against the white background. Clamp each tube in a
3-finger clamp on a ringstand. Immerse one tube in a beaker of ice water (T = 0˚C) and the other in
a beaker of hot water (T = 70˚C). As an alternative to ice water, one tube can be put in either dry ice
or liquid nitrogen. As an alternative to hot water, one tube can be gently heated with the heat gun.
Note the increase in color intensity as N2O4 dissociates to give more brown NO2(g) in the hot (70˚C)
test tube. The cold test tube becomes much less intensely colored as the NO2(g) becomes colorless
N2O4(g).
Safety
Wear protective gloves to avoid burns from hot and cold materials.
Waste Disposal
Water can be poured down a sink drain. Liquid nitrogen can be spread across the lawn in a
courtyard. Extra dry ice can be returned to Chemistry Stores or allowed to sublime in a hood.
Putting dry ice in a sink can crack it.
33
TITLE:
TOPIC:
pH Demonstration
Equilibrium
DEMONSTRATION
(Kit)
5.4
Preparation
Equipment needed:
pH meter, pH electrode, temperature probe, eight 150-mL beakers, one 400mL beaker, washbottle of distilled water, Kimwipes, pH 4 and pH 7 standard
buffers.
Chemicals needed:
120 mL each of the following solutions:
0.1 M HCl
0.1 M acetic acid
0.01 M HCl 0.01 M acetic acid
0.001 M HCl 0.001 M acetic acid
0.1 M NaCl 0.1 M sodium acetate
Each solution is prepared, placed in the appropriately labeled beaker and covered with Parafilm.
The pH meter display is calibrated with the standard buffers.
Demonstration
Measure the pH of the strong acid solutions and discover the pH is approximately 1, 2 and 3 for the
solutions listed above. Measure the pH of the acetic acid solutions and discover that the pH is
consistently higher than the pH of the HCl solution of the same concentration. Measure the pH of
0.1 M NaCl and 0.1 M sodium acetate. The pH of the NaCl is near 7 while the pH of the sodium
acetate is greater than 7.
Clean Up and Waste Disposal
Neutralize the acid solutions and flush them down a sink.
34
TITLE:
TOPIC:
Simple Precipitation Reactions
Equilibrium
DEMONSTRATION
(Kit)
5.16
Preparation
Equipment provided: 3 large demonstration test tubes
Chemicals provided: 0.1 M AgNO3, 1 M NaCl, 0.1 M Pb(NO3)2, 0.1 M KI (or NaI), 0.1 M BaCl2,
0.1 M Na2SO4
Equipment needed:
1 black test tube rack (Gilman 0162)
1 white test tube rack (Gilman 0162)
Demonstration
The following reactions give precipitates.
AgNO3 + NaCl → AgCl (white s) + NaNO3
Pb(NO3)2 + KI → PbI2 (yellow s) + 2 KNO3
BaCl2 + Na2SO4 → BaSO4 (white s) + 2 NaCl
Clean Up and Waste Disposal
Add the lead, barium, and silver compounds to the proper waste containers. If desired, the lead and
barium wastes can be combined. Prepare them for Environmental Health and Safety waste pick up.
The Demonstration Waste web page has a manifest and labels.
35
TITLE:
TOPIC:
Buffer Capacity
Equilibrium
DEMONSTRATION
5.17
The procedures for this demonstration were excerpted from the listed reference (Experiment 8.28,
Buffering Action and Capacity) and missing details or variations on the procedure may be found
there. This demo is limited only by the number of people that can see the output display of the pH
meter.
Introduction: This demonstration is intended to give a physical reality to the effect of buffering.
Standard portions of acid and base are added to four different systems:
1.
2.
3.
4.
100 mL of deionized water (boiled to remove CO2 and NaCl added to stabilize meter).
100 mL of 1 M acetic acid.
100 mL of 1 M sodium acetate.
50 mL of 1 M HAc and 50 mL of 1 M NaAc, prepared at the bench, so the student can see it is
made of the solutions of #2 and #3 above.
Strong acid portions contain 5 mL of 3 M HCl and strong base portions contain 5 mL of 3 M KOH.
These strong acid and base portions are prepared in syringes so that it is obvious to the students that
additions are the same. It should be noted that the pH of water can vary and that the starting pH
should not surprise the demonstrator. The following data were collected during an in-class demo:
Solution
di water (100 mL0
di water + 5 mL 3 M HCl
di water + 5 mL 3 M KOH
pH
5.50
1.52
12.36
∆pH
1 M HAc (100 mL)
1 M HAc + 5 mL 3 M HCl
1 M HAc + 5 mL 3 M KOH
2.57
1.50
3.94
–1.07
1.37
1 M NaAc (100 mL)
1 M NaAc + 5 mL 3 M HCl
1 M NaAc + 5 mL 3 M KOH
8.22
5.45
11.99
–2.77
3.77
Buffer (50 mL HAc + 50 ML NaAc)
+ 5 mL 3 M HCl
+ 10 mL 3 M HCl
+ 15 mL 3 M HCl
+ 20 mL 3 M HCl
4.75
4.40
4.02
3.47
1.32
–0.35
–0.73
–1.28
–3.43
Buffer (50 mL HAc + 50 mL NaAc)
+ 5 mL 3 M KOH
+ 10 mL 3 M KOH
+ 15 mL 3 M KOH
+ 20 mL 3 M KOH
4.81
5.04
5.36
5.87
12.24
0.23
0.55
1.06
7.43
–3.98 average pH: 6.94
6.86
36
Buffer Capacity (continued)
The following observations are helpful:
1. The additions to water show ∆pH from the standard acid/base portions with no equilibrium
(beside Kw) operating in solution.
2. The average between the pH when acid is added to water and base added to water is
approximately 7, indicating the d.i. water is nearly neutral, but the meter poorly measures
solutions of low ionic strength.
3. The presence of weak acid has no effect on the ∆pH from the addition of strong acid, but
presence of weak acid neutralizes part of the effect of adding strong base.
4. Similar effects can be observed in the weak conjugate base solution.
5. For the additions of acid (or base) to buffer, the small ∆pH is observed until the fourth addition
which has swamped the buffering capacity.
6. The addition of only strong acid or strong base to all solutions would be almost equally
instructive, for much less time.
Clean Up and Waste Disposal
Neutralize the acids and bases and wash them down a sink with plenty of water.
Reference
Shakashiri, B. Z., “Chemical Demonstrations”, Volume 3, pages 173-185, Experiment 8.28
37
TITLE:
TOPIC:
Hydrolysis of Salts
Equilibrium
DEMONSTRATION
5.18
The following demonstration is excerpted from the experiment Hydrolysis: Acid and Base
Properties of Salts. Details that are absent here or suggestions for alternate procedures can be found
in the reference below.
Introduction
The demonstration is meant to display the range of pH conditions possible in salt solutions. Salts
which are the combinations of strong acid-strong base (neutral pH), is strong acid-weak base
(acidic), weak acid-strong base (basic) and weak acid-weak base (neutral since Ka=Kb) are included.
The only limitation on the demo is the ability of the audience to read the display of the pH meter.
Preparation
Chemicals needed:
Chemicals needed:
6 150 mL beakers, 6 stirring rods, pH meter, pH electrode, temperature probe,
wash bottle of distilled water, Kimwipes, pH 4 and pH 7 standard buffers.
Salt
SnCl4•5H2O
NH4Cl
NH4C2H3O2
NaCl
NaC2H3O2
Na3PO4•12H2O
DI water (600 mL)
*measured, not calculated
Weight (g)
3.506
0.535
0.771
0.585
1.361
3.801
Approximate pH*
1.5
5.2
7.1
7.6
10.0
11.5
The six salts are all white solids and can be preweighed out into vials in the portions indicated on the
table. A 100.0 mL volume of water is measured into each of six 150 mL beakers, and each beaker is
given a stirring rod. When each salt is dissolved, the concentration is 0.100 M.
Demonstration
The lecturer dissolves the salts at the lecture table, so that students can see each solution contains
water with a white solid added. The initial pH of water may be of interest before you measure
solutions or with more time, you may add each solid while the electrode is in the water so that the
∆pH can be observed. The approximate pH values of the solutions are listed, although variation
does occur and should be expected. The pH of dionized water is hard to measure and some NaCl
may be added to stabilize the meter. Also, boiling out CO2 and storing sealed will give a more
neutral dionized water.
Reference
Shakashiri, B. Z., “Chemical Demonstrations”, Volume 3, pages 103-108.
38
TITLE:
TOPIC:
Atmospheric Pressure or “How to Crush a
Pop Can With No Hands”
Gases
DEMONSTRATION
(Kit)
6.1
Procedure A
Preparation
Equipment needed:
Tripod or ringstand and ring, burner, heat resistant gloves, oblong metal can,
solid rubber stopper to fit can opening.
Chemicals needed:
none
Demonstration
Place 100 to 200 mL of tap water in the can and set it on the tripod or ringstand. Heat the
unstoppered can until the water boils and steam escapes from the can. Remove the can from the heat
and stopper. Cool under water to quickly collapse the can or allow to cool in the air for a slow
collapse.
Procedure B
Preparation
Equipment needed: Oblong metal can, one hole rubber stopper to fit, glass tubing to fit rubber
stopper, length of vacuum tubing, water aspirator or vacuum pump.
Chemicals needed:
none
Demonstration
Remove air from the can by use of the vacuum pump or water aspirator. The can slowly collapses
with loud snapping noises.
39
Procedure C
Preparation
Equipment provided: Clay-covered triangle, aluminum soft drink can, large crystallizing dish,
50 mL plastic graduated cylinder, Meeker burner, beaker tongs, tripod (or
ringstand with iron ring), flint striker.
Chemicals provided: none
Chemicals needed:
Water (available at lecture hall sink).
Demonstration
Fill the crystallizing dish half to three-quarters full of water. Put about 25 mL of water in the
aluminum pop can. Put the clay-covered triangle on the tripod, and set the pop can on the triangle.
Light the Meeker burner, and heat the pop can until the water boils (approximately 30 seconds).
Grasp the can with the beaker tongs, and place it inverted in the crystallizing dish. The can collapses
with a loud snap.
The water seals the hole in the pop can, which is too small to admit enough water to rapidly equalize
the internal and external pressures. As the water vapor inside the can cools, the vapor pressure
drops. The greater external atmospheric pressure immediately crushes the can.
Clean Up and Waste Disposal
Discard the crumpled can in the dumpster.
40
TITLE:
TOPIC:
Liquid Nitrogen Rocket
Gases
DEMONSTRATION
6.2
Preparation
Equipment needed:
3 ft. length of 3/4 inch dia. black iron pipe capped at one end, cork to fit,
2 L dewar flask, 1 L dewar flask, hammer, styrofoam rocket, insulated gloves,
plastic funnel, large metal tripod ringstand, three-finger clamp.
Chemicals needed:
liquid nitrogen
Fasten the three-finger clamp to the ringstand. Put the iron pipe in the three-finger clamp. Carefully
lower the pipe into an empty 2-liter dewar and position the end of the pipe 0.5-1 inch above the
bottom of the dewar. Screw the clamp together TIGHTLY to prevent the pipe from sliding because
a broken dewar implodes violently and is expensive to replace.
Demonstration
To precool the pipe, lift the ringstand/pipe assembly and carefully lower it so that the pipe goes into
a large (2-liter) dewar of liquid nitrogen. When the pipe is cold, pour liquid nitrogen into the pipe
using the funnel and small dewar. (INSULATED GLOVES!) When the level of the liquid nitrogen
inside the pipe rises above the chilled portion of the pipe it will boil out of the pipe vigorously.
Remove the pipe from the dewar and set the end firmly on the floor. Place the cork firmly into the
end of the pipe and tap it lightly with the hammer to secure it. Place the rocket over the corked end
taking care to keep it aimed up. When the gas pressure blows out the cork (run water over the pipe
to speed things up if necessary), the rocket will be launched high into the air. Do not allow liquid
nitrogen to get on bare skin or clothing.
Safety
The liquid nitrogen is extremely cold. Do not allow liquid nitrogen to touch bare skin or clothing.
The pipe is also very cold after it is put in the liquid nitrogen. Use the insulated gloves when
handling the cold pipe.
This experiment is not recommended for 1352, 1652, or 1810 because of their low ceilings.
Clean Up and Waste Disposal
Excess liquid nitrogen is scattered on the ground outside in a courtyard.
41
TITLE:
TOPIC:
Ammonia Fountain
Gases
DEMONSTRATION
(Kit – Gilman 0732A)
6.3
Preparation
Equipment provided: (Gilman 0732A)
2-round bottom flasks (1, 2, or 3 L)
1-tubing unit consisting of
2-8 mm o.d. glass tubing ~ 1 ft. long
1-#10-2 hole stopper
2-thick walled, bent glass tubing
1-2” piece of tygon tubing 10 mL
1-cork ring
1-rubber bulb
1-screw clamp
1-ringstand (Gilman 0732)
Equipment needed:
2-3 finger clamp (0732-B3)
1-ringstand
Chemicals needed:
NH3 gas
0.1 M HCl
indicator (universal, litmus or other suitable indicator)
stopcock grease
Fill the bottom flask to within 1 inch of the top with water to which a small amount of indicator has
been added. Add enough acid to make the indicator show ~ pH 4. Close the screw clamp on the
tygon tubing. Place a small amount of water in the rubber bulb on the bent glas tubbing and seal the
tip with stopcock grease. Thoroughly dry the tubing above the top stopper as well as the top flask.
Suspending the flask over the stopper, fill the top flask with ammonia gas, stopper it tightly, and
secure in place.
Prepare an extra fountain in case the first malfunctions.
42
Ammonia Fountain (continued)
Demonstration
Open the screw clamp. Squirt all of the water into the top bulb from the bent medicine dropper.
The water (colored pink with indicator) in the bottom flask flows through the tube into the top flask
like a fountain. The ammonia in the top flask colors the indicator blue. The fountain will flow until
3/4 or more of the top flask is filled.
Comments
The dramatic decrease in pressure in the top flask which initiates the fountain is due to the decrease
in NH3 pressure as the gas dissolves in the few of water squirted into the flask. (About 90 mL of
NH3(g) at STP will dissolve in L drop of water.) Gaseous HCl can be substituted for NH3(g).
(Solubility of HCl(g) = 823 g/L at 0˚C; solubility of NH3(g) = 899 g/L.)
One can also omit the droppers and start the fountain by pouring ether over the top flask. This
decreases the pressure of the ammonia and initiates the entrance of water; the dissolution of the
NH3(g) will sustain the flow once it is started.
Safety
Support the apparatus securely. There is a decrease in pressure in the top flask during the majority
of the reaction, so one should use a flask that is free of cracks or flaws. As an added precaution use
a face guard and shield in case of an implosion.
Clean Up and Waste Disposal
Neutralize the basic solution, and flush it down the sink.
Reference
H. N. Alyea, Tested Demonstrations in Chemistry, J. Chem. Educ., Tucson, AZ, 6th Edition, 1969,
page 13.
43
Ammonia Fountain (continued)
Modified Ammonia Fountain Demonstration
Principles Illustrated:
Reaction to form ammonia from NH4Cl and NaOH
Result to pressure differential, >Patm and <Patm
Partial pressures: PNH 3 + Pair + Pwater vap. + Phydrostatic = Patm
Materials:
! fitted with a one holed stopper
3 liter flask
right angle glass tubing + hose leading into >3 liter reservoir of water
12 grams of NH4Cl (~ 0.2 moles) + ~ 9 mL water to make slurry.
15 grams of NaOH pellets (~ 0.4 moles)
phenolphthalein indicator (in reservoir water)
Questions:
What is the equation that describes the reaction generating NH3?
Why did the water flow back into the flask?
Why did the black flow stop before filling the flask?
Why does the mixture flow back to the reservoir when the stopper is loosened from flask?
Predict (and perhaps try) what would happen if more NH4Cl were used?
44
TITLE:
TOPIC:
A.
Gas Phase Reactions
Gases
DEMONSTRATION
6.4A
NH3(g) + HCl(g) → NH4Cl(s)
A1. Preparation
Equipment needed:
Two glass reaction cylinders with ground glass edges, two glass plates.
Chemicals needed:
ammonia gas, hydrogen chloride gas
(HOOD!) Fill one cylinder with NH3(g) with the glass place nearly covering the cylinder opening.
Remove tubing and quickly cover. (Note: Cylinder edge must be well greased.) Label the cylinder
NH3. Fill and label the second cylinder with HCl(g).
Demonstration
Set the NH3 cylinder on the bench and invert the HCl cylinder and place it on top the NH3 cylinder.
Have an assistant or volunteer remove the plates while you hold the cylinders in place. The two
cylinders quickly fill with a white cloud of NH4Cl as the gases mix. Little, if any, odor of ammonia
or hydrogen chloride is detected as the gases react completely. (Caution: If you allow the cylinders
to touch together as soon as the plates are removed, a strong vacuum can form sealing the cylinders
together.)
A2. Alternate Preparation
Equipment needed: Glass tube approximately 12 inches long x 1 inch outside diameter, aluminum
stand (or ringstand with three-finger clamp), 2 #4 one-hole rubber stoppers, 2 plastic medicine
droppers, glass wool, 30 mL beakers, Petrolatum or stopcock grease, Teflon plumber’s tape
Chemicals needed:
(HCl)
concentrated ammonium hydroxide (NH4OH), concentrated hydrochloric acid
Shorten the barrels of the two droppers so that they are approximately 10 mm longer than the
stoppers. Label the droppers and fill one dropper with HCl and the other with NH4OH (HOOD!).
Cap the dropper tips with Petrolatum and put one dropper through each of the stoppers. See Figure 1.
Wrapping several layers of Teflon tape around the dropper barrels minimizes gas leakage.
Figure 1
45
Put a plug of glass wool in each end of the glass tube and put a stopper in each end of the tube. The
tips of the droppers should be touching the glass wool plugs. Put the glass tube on the stand or in a
ringstand. Figure 2 shows the completed setup.
Figure 2
Demonstration
Set the glass tube on the document camera’s base. Squeeze the dropper bulbs at the same time,
soaking the glass wool. HCl and NH3 gas diffuse along the tube and form a white ring of NH4Cl.
Safety
Both HCl and NH4OH are corrosive. HCl and NH3 gas are irritating to the skin, eyes, and respiratory
system. Use the standard protective garb and eyewear and work in a hood when setting up the
demonstration.
Clean Up
Neutralize the acid and base and flush it down a sink. NH4Cl can also be flushed down a sink. The
glass wool can be discarded in a dumpster.
Reference:
Shakashiri, B. Z., “Chemical Demonstrations”, Volume 2, pages 59-62.
46
TITLE:
TOPIC:
Gas Phase Reactions
Gases
B.
H2(g) + 1/2 O2(g) → H2O(g) + bang
B1.
Hydrogen–Oxygen Pop Bottles
DEMONSTRATION
(Kit)
6.4B
Preparation
Equipment needed:
burner, coke bottle, flint striker, grey ringstand with three 3-finger clamp
Chemicals needed:
oxygen gas, hydrogen gas
The glass, 6 oz. coke bottles are wrapped in transparent tape for
safety and are marked at 1/3 the total volume. Fill the bottles with
water and invert them in a tub, clamping each one in a 3-finger
clamp. Bubble oxygen in until the water is displaced to the mark.
Bubble in hydrogen leaving a little water in the bottle. Insert
stopper. The bottles are stored stopper down, and a few milliliters
of water around the stopper acts as a seal.
Different concentrations of O2 in the coke bottle make bangs of
different volumes. Pure H2 makes a tiny pop. Using air instead of
O2 makes a bang considerably less loud than when O2 is used.
Plastic, 20 oz. coke bottles can be filled with 3/4 O2 and 1/4 H2.
This is not stoichiometric, but it makes an excellent explosion. The plastic bottles hold hydrogen for
only a week, unlike glass bottles which hold the hydrogen for several months.
Demonstration
Hold the bottle at an angle of 30-45˚ from the horizontal, with the opening down. Unstopper the
bottle and swing the mouth near a lit bunsen burner. Hold the bottle tightly; there is a loud bang.
B2. Hydrogen–Oxygen Balloons
Preparation
Equipment needed:
balloons, string, weight, candle on a stick, #0 rubber stopper on a 3 inch glass
tube, matches or fire starter
Chemicals needed:
hydrogen gas, oxygen gas, helium gas (optional)
The rubber stopper on the glass tube is an adapter to mate a balloon’s neck to a gas cylinder’s hose.
The balloon is filled with helium gas (for a helium balloon), hydrogen gas (for a hydrogen balloon)
or a mixture of 2/3 hydrogen and 1/3 oxygen (for a hydrogen + oxygen balloon). The neck of the
balloon is tied in an overhand knot, and 7-12 feet of string is tied to the balloon. The free end of the
string is tied to the weight to keep the balloon from floating away. The string is rolled up on the
weight during transport to the lecture hall.
Demonstration
A lecturer may ask for one or more balloons. Each balloon floats above the lecture bench. Light the
candle and put the flame to the balloon. A hydrogen + oxygen balloon explodes. A hydrogen
47
balloon produces a BOOM and a cloud of flame that is particularly effective in a darkened room. A
helium balloon just pops anticlimactically.
Safety
Warn the students to protect their ears. A balloon makes a loud bang when ignited.
Do not carry hydrogen-filled balloons inside a closed bag or vehicle or let the balloons rub together.
The hydrogen leaks and can be set off by a spark of static electricity (Garrett, 2003). In addition,
four balloons rubbed together in a draft in Gilman 0732 and went off. While no one was hurt, the
explosion made a six inch hole in the plaster ceiling, and the dust set off the smoke alarm.
References
Garrett, Garry. 2003. Hydrogen–Oxygen Balloon Hazards. J. Chem. Educ. 80: 743.
(http://jchemed.chem.wisc.edu/journal/issues/2003/Jul/abs743_1.html)
48
TITLE:
TOPIC:
C.
Gas Phase Reactions
Gases
DEMONSTRATION
6.4C
H2(g) + Cl2(g) + light → 2 HCl + bang; The Hydrogen–Chlorine Cannon
Preparation
Equipment needed:
Cannon, 2 cork stoppers, photoflash, large tub of water, two 100 mL
graduated cylinders, 250 mL beaker, 1.5 inch width test tube brush, 3 3-finger
clamps, 3 ringstands, small black plastic sheet, rubber bands.
Chemicals needed:
chlorine gas, hydrogen gas
Fill a tub with water and invert a 250 mL beaker in the water. The beaker should be full of water.
Find two corks (Gilman 0635, wooden Tote-Tray cabinet) that fit the cannon’s muzzle and put them
inside the inverted beaker. Let the corks soak for a few hours so the water displaces air from the
pores in the corks.
The Cannon With Cork
Move the water tub to a hood if it is not already there. Get three ring stands with 3-finger clamps.
Fill two 100 mL graduated cylinders and the cannon completely with water. Use a test tube brush to
get rid of any tiny air bubbles in the cylinders and cannon. Invert the cylinders and cannon in the
water tub and clamp them in place for filling. (Note: Fill the graduated cylinders with the gases with
the hood lights off and room lights dimmed, if possible. Although we have never had a reaction
occur in room light, we cannot exclude that possibility, particularly if the room receives any direct
sunlight.) Bubble chlorine gas into the two graduated cylinders until the water is displaced to the 50mL mark. Bubble hydrogen into the graduated cylinders to the 100 mL mark. This makes two
graduated cylinders that hold a 1:1 mixture of hydrogen and chlorine.
While keeping the cannon’s muzzle and the open end of a graduated cylinder under water, transfer
the hydrogen and chlorine mixture from the graduated cylinder to the cannon. This is a matter of
pouring the gas up into the cannon and displacing the water there. Transfer the gas in the second
graduated cylinder to the cannon until full. Stopper the cannon with the better cork. The black
plastic covers the glass plate in the cannon’s breech and is held on with rubber bands.
Points to consider:
1. Cl2 dissolves in H2O. Fill the cannon as soon as the gas mixture is made. To minimize corrosion
problems, blow N2 gas through the Cl2 valve for 60 seconds as soon as possible.
49
2. O2 will poison the reaction. Make sure the cannon and graduated cylinders contain no air
bubbles before filling them with gas. Soak the corks for a few hours to displace air from the
pores. Also insert the corks in the cannon a few times before filling it with H2 + Cl2 to help get
air out of the pores. Soak corks in an inverted 250 mL beaker.
3. Use a powerful photoflash with fresh batteries. The flash in the General Chemistry Office’s
camera kit works when on manual setting 104, but some others aren’t powerful enough.
Demonstration
Align the tube along the axis of the lecture bench and elevate the cannon’s muzzle. The cork is
aimed toward the room’s side wall rather than toward the students. Charge the photoflash. Remove
the plastic covering the cannon’s breech. If the room is brightly lit, the reaction may occur;
however, you will probably need to use the flash unit to initiate it. Hold the unit 1 to 2 cm from the
glass plate in the cannon’s breech and discharge the flash. A loud explosion should occur. The cork
can fly three-quarters the width of Gilman 1002 and hit the wall half way to the ceiling. If the
reaction does not go when flashed, chances are good that some oxygen is present dooming the
experiment to failure.
Filters. Red, yellow and blue filters are available in transparency file. Included are transparencies of
the absorption spectra from 400 mm to 700 mm for each filter. Reaction cannot be initiated with red
light. Yellow or blue light will initiate the reaction.
Safety
Chlorine gas can burn the eyes and skin. Inhalation can be fatal. Make the gas mixture and flush
the Cl2 valve in the hood!
Hydrogen gas makes an explosive mixture with air or chlorine. Fill the graduated cylinders with the
gases with the hood lights off and room lights dimmed, if possible. Although we have never had a
reaction occur in room light, we cannot exclude that possibility, particularly if the room receives any
direct sunlight.
Set the cannon between safety shields. One shield protects the students, and the second protects the
demonstrator. The cannon is made of thick plastic, but an earlier version of this demonstration had to
be discontinued because the glass tube shattered.
Cleanup and Waste
Rinse the cannon and the glassware and let them air dry. Flush the Cl2 valve with nitrogen gas for 60
seconds (HOOD!). Discard the used cork in a wastebasket.
50
TITLE:
TOPIC:
The CO2 Bubbler
Gases
DEMONSTRATION
6.8
Preparation
Equipment needed:
One or two glass reaction cylinders (approximately 2 L capacity), cooler,
cloth gloves, 2 L beaker
Chemicals needed:
Pellets of dry ice, 0.1 M NaOH, universal indicator
Get the dry ice pellets (a pound is more than enough) in the cooler. Fill the 2 L beaker with water,
and add enough 0.1 M NaOH and universal indicator to produce a nice violet color. Fill the reaction
cylinder to 4-6 inches from the top with this violet solution.
Demonstration
While wearing the gloves, drop several pellets of dry ice in the reaction cylinder. The dry ice
sublimes, producing cold CO2 gas which condenses water out of the atmosphere, producing a fog at
the top of the cylinder. Some of the CO2 dissolves in the water, producing carbonic acid, and
changing the color of the universal indicator to a pinkish yellow.
Note: Do NOT use more than a few pellets of dry ice at a time. If a whole pound of dry ice is added
at once, it will freeze the water and break the reaction cylinder.
Safety
Wear protective cloth gloves to avoid frost bite when handling dry ice. Use in a well-ventilated area.
Clean Up and Waste Disposal
Neutralize the solution to a pH of 6-9, and wash it down a sink. Let the unused dry ice sublime in
the cooler. Do NOT put dry ice in a sink as the low temperature could crack the sink.
51
TITLE:
TOPIC:
Shrinking a Balloon In Liquid Nitrogen
(Charles’s Law)
Gases
DEMONSTRATION
6.9
Preparation
Equipment needed:
Pyrex crystallizing dish (circular, 190 x 100 mm), 1 L dewar flask, Styrofoam
pad (~8 x 8 x 2 inches), insulated gloves, balloon
Chemicals needed:
3/4 L of liquid nitrogen
Assemble the equipment ahead of time. The liquid nitrogen will last several hours in the dewar.
However, the liquid nitrogen slowly boils away, so the amount may have to be adjusted depending
on how long it must stand. The loss is not significant if the nitrogen is dispensed less than 30
minutes before the lecture.
Demonstration
Put the crystallizing dish on the Styrofoam pad and pour the liquid nitrogen into the dish. Inflate the
balloon until it is slightly larger than the dish, if the balloon is round, and tie a knot in the balloon’s
neck. Push the inflated balloon into the dish until the balloon touches the liquid nitrogen. The
balloon deflates fairly quickly as the air inside gets colder. Pulling the balloon out of the liquid
nitrogen lets the cold air warm up and inflate the balloon again. This is an illustration of Charles’
Law. (Note: Part of the balloon’s shrinkage is due to the gas becoming liquid.)
Safety
Liquid nitrogen is very cold. Do not let it touch bare flesh or clothing. The crystallizing dish also
becomes very cold. It can be handled with the insulated gloves.
Cleanup and Waste Disposal
Liquid nitrogen can be thrown out on the ground or allowed to boil away in a hood. Do NOT pour it
in a sink because the intense cold can crack the sink or drain pipes. The cold crystallizing dish
should warm up before it is washed. The balloon can be cut open to deflate it and discarded in a
wastebasket.
52
TITLE:
TOPIC:
The Volume of a Mole of Gas
Gases
DEMONSTRATION
6.10
Preparation
Equipment needed:
Inflatable ball with a volume of 22.4 L.
53
TITLE:
TOPIC:
Conductivity
Ions, Conductivity, and Electrolysis
DEMONSTRATION
(Kit)
7.1
Preparation
Chemicals provided: Deionized, distilled water; 95% ethanol; 0.1 M
solutions of acetic acid, sodium acetate, HCl, NaOH,
NH4OH, NaCl, and K2SO4 in glass, wide-mouthed
bottles.
Equipment provided: ringstand with light bulb unit
Equipment needed:
wash bottle filled with distilled water, 1 L plastic
beaker
The plastic electrode covers have a series of holes drilled in them. The hole
at the top is for rinsing the metal electrode. The holes in the inner sides are
to minimize the distance that the current must flow between the electrodes.
Demonstration
The light bulb does not have a switch. Plugging it into the bench’s electric socket powers it on, but
the bulb does not light up until current flows between the two electrodes through an electrolyte.
Power the light bulb on, unscrew the cap of one of the solution bottles, and dunk the electrodes into
the solution. Water and ethanol are nonelectrolytes, and the bulb does not light. Acetic acid and
ammonium hydroxide are weak electrolytes, and the bulb’s filament glows. The other solutions are
strong electrolytes, and the bulb shines brightly.
Using the wash bottle, rinse the electrodes and the electrode covers between solutions to minimize
contamination. Catch the rinse water in the plastic beaker.
Safety
Ethanol is flammable, and the other solutions are irritants. Wear safety goggles. A lab coat and
rubber gloves are available. CAUTION—electricity!
Waste
Put the waste rinse water in the acid-base waste bottle in Gilman 0732 for eventual neutralization.
Reference
Alyea, H. N. “Tested Demonstrations”, page 15, (6-1, 6-2)
54
TITLE:
TOPIC:
Conductivity Changes in a Chemical Reaction,
Ba(OH)2 + H2SO4
Ions, Conductivity, and Electrolytes
DEMONSTRATION
7.2
Preparation
Equipment needed:
Magnetic stirrer and 1 inch stir bar, magnetic stirrer, conductivity box
(Gilman 0635), two 400-mL beakers, plastic beaker top with electrodes, 1 red
and 1 black wire with banana plugs, two alligator clips, 50-mL or 100-mL
buret, washbottle, small funnel (if needed to fill buret), ringstand and buret
clamp.
Chemicals needed:
~25 mL of 0.1 M Ba(OH)2 (filtered to remove precipitated BaCO3), 50 mL of
0.1 M H2SO4, phenolphthalein (optional)
Demonstration
Check the conductivity of the two solutions if desired, and then fill the buret with the 0.1 M H2SO4.
Dilute 20-25 mL of 0.1 M Ba(OH)2 to 150 mL and put the solution in the 400 mL beaker. Add the
150 mL of 0.1 M Ba(OH)2 to the 400-mL beaker. (Optional: Add a few drops of phenolphthalein.)
Put the plastic top with electrodes on the beaker. Connect the conductivity box to the electrodes
with the wires and alligator clips, and begin titrating, stirring constantly.
Ba(OH)2(l) + H2SO4(l) → BaSO4(s) + 2 H2O(l)
Follow the change in conductivity (optional: phenolphthalein color) as the endpoint is approached,
reached and exceeded.
Clean Up and Waste Disposal
Package the barium sulfate and excess sulfuric acid for Environmental Health & Safety to pick up.
A waste manifest and label are on the Demonstration Waste web page.
Reference
Shakhashiri, B. Z., “Chemical Demonstrations”, University of Wisconsin Press, Madison, WI,
Volume 3, Experiment 8.23, pages 152-154.
55
TITLE:
TOPIC:
Conductivity of a Fused Salt
Ions, Conductivity and Electrolysis
DEMONSTRATION
(Partial Assembly)
7.3
Preparation
Chemicals provided: Potassium nitrate
Equipment provided: Bunsen burner, ringstand, iron ring, clay-covered triangle, iron crucible, two
single buret clamps, two electrodes, two rubber stoppers.
Equipment needed:
Flint striker, conductivity box, power cord, two wires. Each wire has an
alligator clip on one end and a banana plug on the other end.
The ringstand and other provided equipment is assembled and stored in one of the cabinets in
Gilman 0162. The assembly includes the crucible, which is half full of potassium nitrate that has
been heated until it melted and then cooled to room temperature. See the illustrations.
Each wire is plugged into the conductivity box. The other end of each wire is clipped to an electrode.
The conductivity box is plugged into an electric socket in the bench, and the box’s switch is set to
“strong”. Electric current is intended to flow from the conductivity box through one wire to an
electrode, through the potassium nitrate (when it is molten) to the other electrode, and through the
other wire to return to the conductivity box.
Demonstration
When heated and changed from a solid to a molten state, potassium nitrate spontaneously forms K+
and NO333- ions, which conduct electricity.
The demonstration begins with no light from the conductivity box. Light the Bunsen burner. As the
potassium nitrate becomes molten, the conductivity box lights up. Turning off the Bunsen burner lets
the potassium nitrate cool off, and electricity stops flowing through the potassium nitrate.
56
Safety
The Bunsen burner flame is very hot. The wires from the conductivity box must be kept behind the
ringstand and away from the flame to prevent the wires’ insulation from melting. The iron crucible
also gets hot. It should not be touched, and the hot potassium nitrate should not be spilled.
Waste
There is no waste. The solidified potassium nitrate remains in the crucible for the next run in a week
or a year.
Reference
Alyea, H. N. “Tested Demonstrations”, 6th edition, p. 76.
57
TITLE:
TOPIC:
Diffusion of Hydrogen
Kinetic Molecular Theory
DEMONSTRATION
8.1
Preparation
Equipment needed:
Porous clay cup with connected manometer filled with CuSO4 solution, glass
cylinder to fit over cup, glass plate 6 inches square.
Chemicals needed:
hydrogen gas, Petrolatum (petroleum jelly)
Make a circle of petroleum jelly on the glass plate. The jelly must be fairly thick because it seals the
open end of the glass cylinder to the glass plate. Put the plate on the bench. Fill the glass cylinder
with hydrogen glass by air displacement. When full, press the open end of the cylinder down on the
glass plate, while giving a small amount of twist to get a good seal with the petroleum jelly. Label
the glass cylinder and put it aside, open end down, until the lecture.
Demonstration
While holding the hydrogen-filled glass cylinder with the open side down, remove the glass plate
and lower the cylinder of hydrogen gas over the porous cup. Allow the cylinder to sit on the wooden
support ring. The level of the colored solution in the outside arm of the manometer rises as the
hydrogen diffuses into the cup faster than the nitrogen and oxygen in the cup can diffuse out. Watch
the apparatus carefully as it may be necessary to remove the hydrogen cylinder from the cup to
prevent the solution from spilling out of the manometer.
Clean Up and Waste Disposal
To prevent evaporation when not in use, cover the manometer’s open end with Parafilm.
58
TITLE:
TOPIC:
The Cryophorus
Kinetic Molecular Theory
Preparation
Equipment needed:
Chemicals needed:
DEMONSTRATION
8.2
Cryophorus filled with water, bromine, or other solution, short ringstand,
3-finger clamp
liquid nitrogen (dry ice/isopropanol may be used but is messier to clean up)
Demonstration
The cryophorus is tilted to vertical to return all the water to the reservoir without the depression and
is then clamped in a horizontal position. Liquid nitrogen is added to the depression. Several refills
will be needed. Vapor condenses in the reservoir with the depression and in a minute or so the liquid
in the other reservoir freezes.
Clean Up and Waste Disposal
Scatter the excess liquid nitrogen outside the building.
59
TITLE:
TOPIC:
Iodine Clock Reaction
Kinetics
DEMONSTRATION
(Kit)
9.1
Preparation
Equipment needed:
1 400-mL beaker, 2 125-mL wide-mouthed plastic bottles.
Chemicals needed:
4 g KIO3, 4 g starch, 0.8 g NaHSO3, 5-mL 6 M H2SO4
Solution A is stable for years without special treatment. Solution B is stable for at least a year when
stored in filled, tightly capped bottles with only a few milliliters of air space. When exposed to air,
solution B decomposes within a few days.
Solution A:
0.2% KIO3 (2 g KIO3/L)
Solution B:
Make a slurry of 4 g starch in water and add it to 1 liter of boiling H2O. Let
cool to room temperature (use ice water bath to speed cooling, if necessary).
Dissolve 0.8 g NaHSO3 in 3/4 liter of room temperature H2O. Combine the
starch and NaHSO3 solutions, add 5-mL of 6 M H2SO4, and dilute to 2 L.
(Final amounts = 2 g starch, 0.4 g NaHSO3, 2.5-mL 6 M H2SO4 per liter)
Test the demonstration by mixing equal quantities of solutions A and B in a 30 mL beaker. The
solution should remain clear for 10 – 60 seconds and then turn blue-black. If the color change
occurs too quickly (less than 5 sec.), dilute solutions A and B with water then repeat this test. If the
color change has not occurred after 1 minute, obtain clean glassware and remake the solutions.
Repeat this test on the fresh solutions.
Before Class
Label one wide-mouthed plastic bottle “Solution A” and the other “Solution B”. Fill each bottle to
the top of the shoulder with the appropriate solution. This is 120-125 mL per bottle.
Demonstration
Put the beaker on a white background such as a Teri-towel. Pour solutions A and B together into the
beaker. After a period of time the clear solution changes to a blue-black color.
Variation: The Effect of Temperature and Concentration on the Rate of Reaction
Equipment needed:
6 400-mL beaker, 12 125-mL wide-mouthed plastic bottles, 2 crystallizing
dishes, hot plate, bottle labels at the end of this demonstration.
Chemicals needed:
Solution A and solution B as above, water.
Label the 12 bottles. Put 12.5 mL of water in the bottle marked A—90% of Normal and 12.5 mL of
water in the bottle marked B—90% of Normal. Put 37 mL of water in each of the two bottles marked
75% of normal. Fill all six A bottles to the top of the shoulder with solution A. Fill all six B bottles
to the top of the shoulder with solution B. Put the two bottles marked Cold in an ice/water bath an
60
hour before the demonstration is scheduled. Put the A bottle marked Hot in a water bath on the hot
plate and start it heating at the beginning of the lecture demonstration. The B bottle marked Hot
stays at room temperature because heating it makes the NaHSO3 decompose. When hot solution A is
mixed with room temperature solution B, they still reacts faster than when both solutions are at room
temperature. This gives three pairs of solutions at the same concentration but different temperatures
and three pairs of solutions at the same temperature but different concentrations.
Combine the pairs of solutions in 400 mL beakers as in the original Iodine Clock Demonstration. As
the solutions become more dilute, they take more time before turning color. As the solutions become
colder, they take more time before turning color.
Clean Up and Waste Disposal
Package the used solution for Environmental Health and Safety to pick up. A label and waste
manifest are on the Demonstration Waste web page. For small amounts, mix in sodium thiosulfate
to ionize the iodine, neutralize the acid, and flush down a sink with plenty of water.
References
A. Alyea and F. Dutton, Tested Demonstrations in Chemistry, 6th Edition, 1965, page 19.
Shakhashiri, B. Z., “Chemical Demonstrations”, University of Wisconsin Press, Madison, WI,
Volume 4, Experiment 10.1, pages 16-25.
61
Iodine Clock (Demo 9.1) Labels
The Effect of Temperature and Concentration on Reaction Speed
Iodine Clock -- Demo 9.1
0.2% KIO3
Iodine Clock -- Demo 9.1
H2SO4, NaHSO3, starch
A-Hot
B-Hot
Iodine Clock -- Demo 9.1
0.2% KIO3
Iodine Clock -- Demo 9.1
H2SO4, NaHSO3, starch
A-Cold
B-Cold
Iodine Clock -- Demo 9.1
0.2% KIO3
Iodine Clock -- Demo 9.1
H2SO4, NaHSO3, starch
A-Room Temp
B-Room Temp
Iodine Clock -- Demo 9.1
0.20% KIO3
Iodine Clock -- Demo 9.1
H2SO4, NaHSO3, starch
A-Normal Conc.
B-Normal Conc.
Iodine Clock -- Demo 9.1
0.18% KIO3
Iodine Clock -- Demo 9.1
H2SO4, NaHSO3, starch
A-90% of Normal
B-90% of Normal
Iodine Clock -- Demo 9.1
0.15% KIO3
Iodine Clock -- Demo 9.1
H2SO4, NaHSO3, starch
A-75% of Normal
B-75% of Normal
62
TITLE:
TOPIC:
“William Tell Overture Clock”
Kinetics
DEMONSTRATION
9.2
Preparation
Equipment needed:
10 50 mL syringes, 10 250-mL beakers, tape recorder, William Tell Overture
tape.
Chemicals needed:
2 g KIO3, 2 g starch, 0.4 g NaHSO3, 5 mL 6 M H2SO4
Solutions are the same as in Demonstration 9.1. See the note in 9.1 about Solution B’s stability.
The dilutions must be made fresh the day of the lecture (preferably not more than about one hour
before use.)
Solution A:
Solution B:
2 g KIO3 in 1 liter H2O
2 g starch in 500 mL boiling H2O, cool, and add 0.4 g NaHSO3, 2.5 mL 6 M
H2SO4, and dilute to 1 liter with H2O
Note: These solutions are the same as those in Demonstration 9.1, the Iodine clock Reaction.
Label ten beakers A1 thru A10 and ten syringes B1 thru B10. Fill the flasks and syringes as per the
table below. Volumes are given in milliliters, and Solution A should be measured from a buret.
Flask
Solution A
H2 O
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
50
48
45
42
39
36
34
32
29
27
0
2
5
8
11
14
16
18
21
23
2.5xH2O
for 125 mL
of sol’n
0
5
12.5
20
27.5
35
40
45
52.5
57.5
Flask
Solution B
H2 O
B1
B2
B3
B4
B5
B6
B7
B8
B9
B10
50
45
45
42
39
36
34
32
29
27
0
2
5
8
11
14
16
18
21
23
The concentrations of A10 and B10 must be adjusted to correspond to the end of the tape; other
concentrations are not so critical. If the solutions are to stand for any length of time before the
demonstration is run, A10 and B10 should be adjusted so that they change color slightly early
(approximately 2 sec/hr of standing).
63
“William Tell Overture Clock” (continued)
Demonstration
Have 10 students pour B1 into A1, B2 into A2, etc. at a predetermined point in the tape (so end
occurs correctly). For an interesting twist, use Old Nassau (Demonstration 9.3) for solutions A10
and B10.
Clean Up and Waste Disposal
Package the used solution for Environmental Health and Safety to pick up. A label and waste
manifest are on the Demonstration Waste web page. For small amounts, mix in sodium thiosulfate
to ionize the iodine, neutralize the acid, and flush down a sink with plenty of water.
References
1. Brice, L. K., J. Chem. Educ., 57, 152 (1980)
2. Shakhashiri, B. Z., “Chemical Demonstrations”, University of Wisconsin Press, Madison, WI,
Volume 4, Experiment 10.1, pages 16-25.
64
TITLE:
TOPIC:
“Old Nassau”
Kinetics
DEMONSTRATION
(Kit)
9.3
Preparation
Equipment needed:
One 1-liter Berzelius beaker (or a 1 L wide mouth glass bottle for a traveling
show), three 250 mL wide mouthed plastic bottles
Chemicals needed:
15 g KIO3, 4 g starch, 15 g NaHSO3, 3 g HgCl2
Solution A:
Solution B:
Solution C:
15 g KIO3 in 1 liter H2O (can be stored)
4 g starch in 500 mL H2O, then add 15 g NaHSO3 dissolved in 500 mL H2O
3 g HgCl2 in 1 liter H2O (can be stored)
To dissolve the starch, make it into a slurry with a little water. Pour the slurry into boiling water.
Allow the starch solution to cool to room temperature before adding the NaHSO3.
The starch/NaHSO3 solution must be stored in tightly capped, 500 mL or 1 L glass bottles with
minimal air space because NaHSO3 reacts with oxygen. Seal the bottles with Parafilm. If well
sealed and with minimal air in the bottle, the solution will last for over a year.
Test the demonstration by mixing equal volumes of solutions B, C, and then A in that order. A
bright orange color (HgI2) appears after a few seconds which soon turns to blue-black. If the colors
appear too quickly, dilute B (2-4 fold) in order to increase the reaction time.
Before Class
Pour equal volumes (250 mL) of the three solutions into separate, 250-mL, wide mouthed plastic
bottles and label these bottles A, B, and C. Label the 1 L beaker B-C-A for the lecturer’s
convenience.
Demonstration
Pour solutions B, C, then A (in that order) into the Berzelius beaker. A bright orange color (HgI2)
appears after a few seconds which soon turns blue-black.
Using a 1 L glass bottle for the demonstration minimizes spills when bringing the waste home from
a show outside the building. Once home, the waste solution can be properly packaged for disposal.
65
“Old Nassau” (continued)
Comments
This is the famous clock reaction of Hubert Alyea. The colors, orange and black, are the colors of
the House of Nassau, and Princeton University whose Old Nassau Hall was the world’s first
undergraduate chemistry laboratory in the world. Professor Alyea mixes several of these solutions
together as he sings the Princeton alma mater. By carefully adjusting the quantities, he times the
color changes to coincide with words “orange” and “black” as they occur in the song.
The following reactions are said to be responsible for the color changes:
2 H+ + 5 HSO3– + 2 IO3–
H2O + HSO3– + I2
fast
fast
I2 + 5 HSO4– + H2O
2 I– + HSO4– + 2 H+
when enough I– has accumulated
Hg2+ + 2 I– → HgI2 (orange solid)
when the HSO3– concentration becomes very small
5 I– + IO3– + 6 H+ → I2 + 3 H2O
The free I2 reacts with the starch to form the dark blue complex.
Clean Up and Waste Disposal
The chemical waste solution contains mercury salts. It must be packaged for collection by
Environmental Health and Safety. A label and waste manifest is on the Demonstration Waste web
page.
Reference
1. H. Alyea and F. Dutton, Tested Demonstrations in Chemistry, 6th Edition, 1965, page 19.
2. Shakhashiri, B. Z., “Chemical Demonstrations’, University of Wisconsin Press, Madison, WI,
Volume 4, Experiment 10.3, pages 29-36.
66
TITLE:
TOPIC:
Red, White and Blue Clock Reaction
Kinetics (Chemical Reactions)
DEMONSTRATION
9.4
Use the Shakhashiri version of this demonstration. Shakhashiri does not use cadmium nitrate.
Preparation
Equipment needed:
6 250-mL Erlenmeyer flasks
Chemicals needed:
25 mL of 40% formaldehyde, 20.8 g NaHSO3, 6.3 g NaSO3, phenolphthalein
and thymolphthalein indicator solutions, saturated Cd(NO3)2
Solution A must be aged, it must be made at least 24 hours before use.
Solution B is unstable and must be prepared fresh daily.
Solution A:
Solution B:
25 mL of 40% formaldehyde per liter
20.8 g NaHSO3 and 6.3 g Na2SO3 per liter
Label the flasks and fill them as per the table below.
Flask
Red A
Red B
White A
White B
Blue A
2Blue B
Solution A
50 mL
–––
30 mL
–––
45 mL
–––
Solution B
–––
50 mL
–––
10 mL
–––
50 mL
H2 O
–––
–––
20 mL
40 mL
5 mL
–––
Indicator
1 mL Phenolphthalein
–––
1 mL Cd(NO3)2
–––
1 mL Thymolphthalein
–––
To test the demonstration pour the solutions labeled red A and B together and record the elapsed
time until the solutions turn red. Repeat this procedure for the white and for the blue solutions A and
B. The order of appearance of color should be red, then white, then blue. If this is not the observed
order, adjust the volumes of A and B used.
Before Class
Fill the six flasks as per the table above. Cover with Parafilm.
Demonstration
Have three students pour the solution in the appropriate A flask into the corresponding B flask, then
swirl the flask to mix the solutions. The colors should appear in the order: red, then white, then
blue.
67
Red, White and Blue Clock Reaction (continued)
Clean Up and Waste Disposal
Package the waste solution for Environmental Health and Safety to pick up. A label and waste
manifest are on the Demonstration Waste web page. There are versions with and without cadmium
nitrate.
Reference
Shakhashiri, B. Z., “Chemical Demonstrations”, University of Wisconsin Press, Madison, WI,
Volume 4, Experiment 10.9, Procedure A, pages 70-74.
68
TITLE:
TOPIC:
Oscillating Clock Reaction I. Bromate System
Kinetics (redox reactions)
DEMONSTRATION
9.5
Preparation
Equipment needed:
1 1-liter Berzelius beaker, magnetic stirrer and stir bar
Chemicals needed:
50 mL of 18 M H2SO4, 6 g malonic acid, 6 g KBrO3, 2 g MnSO4•H2O
Powder the malonic acid then weigh out the required amount and store in a small beaker covered
with parafilm. Repeat for the KBrO3 and MnSO4•H2O.
Before Class
Add the sulfuric acid to 500 mL of distilled water contained in a 1-liter Berzelius beaker. Caution:
Stir well while adding the acid. This works out to 550 mL of 1.6 M H2SO4.
Note: Be sure all glassware is clean because chloride ions will interfere with the reaction
mechanism.
Demonstration
Place the beaker containing the sulfuric acid solution on the magnetic stirrer and add the stir bar.
Add to the solution, while stirring vigorously, malonic acid followed by KBrO3 followed by
MnSO4•H2O. The solution oscillates in color from an orange-brown to clear, evolving CO2 all the
while.
Clean Up and Waste Disposal
After the acid is neutralized, the solution can be poured down a sink.
References
1.
2.
3.
4.
5.
G. J. Kaskerek and T. C. Bruce, Inorg. Chem., 10, 382 (1971)
A. M. Zhabatinskii, Biofizika, 9, 306 (1965)
H. Degn, Acta. Chem Scand., 21, 1057 (1957)
H. C. Mishrand and c. M. Singh, J. Chem. Educ., 54, 377 (1977)
Shakhashiri, B. Z., “Chemical Demonstrations”, University of Wisconsin Press, Madison, WI,
Volume 2, Experiment 7.6, pages 273-275.
69
TITLE:
TOPIC:
Oscillating Clock Reaction II. Iodate System
Kinetics (redox reactions)
DEMONSTRATION
(Kit)
9.6
Preparation
Equipment needed:
1 1-liter Berzelius beaker, magnetic stirrer and stir bar, 3 250 mL plastic
W.M. bottles, 30 mL beaker.
Chemicals needed:
60 g KIO3, 28 mL of 18 M H2SO4, 360 mL of 30% H2O2, 62.4 g malonic acid,
13.6 g MnSO4•H2O, 0.4 g starch
Solution A:
Solution B:
Solution C:
Solution D:
30 g KIO3 + 14 mL of 18 M H2SO4 in one liter of H2O
360 mL of 30% H2O2 diluted to 1 L with deionized distilled water
31.2 g malonic acid + 6.8 g MnSO4•H2O in one liter of H2O
0.4 g starch in 200 mL of boiling H2O, cool. (= 2 g of starch per liter)
(Make a slurry of the starch before adding it to the water. This will avoid lumps of starch)
Solution B must be prepared fresh the day that the demonstration is to be done (preferably within an
hour of the demonstration). Solution D is stored in the refrigerator. Solution A and solution C will
last indefinitely at room temperature.
Before Class
Label the 30 mL beaker as D, put 15-20 mL of solution D in it, and cover it with Parafilm. Put the
stirring bar in the Berzelius beaker.
Label the three plastic bottles A, B, C, and then add 250 mL of the respective solution to the bottles.
Demonstration
Start the stirrer and add solutions D, A, B, and C to the Berzelius beaker in that order. The solution
oscillates in color from orange to blue evolving CO2 all the while.
Clean Up and Waste Disposal
Package the waste solution for pick up by Environmental Health & Safety. There is a label and
waste manifest on the Demonstration Waste web page.
For small amounts, dilute the solution to kill the reaction, react the free iodine with sodium
thiosulfate and neutralize the acid before flushing the solution down the sink.
Reference
Shakhashiri, B. Z., “Chemical Demonstrations”, University of Wisconsin Press, Madison, WI,
Volume 2, Experiment 7.1, pages 248-256.
70
TITLE:
TOPIC:
Dust Explosion
Kinetics
DEMONSTRATION
9.7A
Procedure A. The Grain Bin
Preparation
Equipment needed:
Dust explosion can, candle, matches, funnel, rubber tubing, 3/4 × 3” plastic
tube (mouthpiece), vinyl tape.
Chemicals needed:
Lycopodium powder
Secure the plastic mouthpiece to the free end of the rubber hose with the vinyl tape. Wad a small
piece of brown paper towel and rub it between your hands to form it into a ball. Place the wad in the
bottom of the funnel to minimize the amount of lycopodium powder that slides into the rubber
tubing. Fill the bottom third of the funnel with lycopodium powder (see sketch).
Demonstration
Light the candle and place it inside the can near the funnel. Secure the can lid tightly (friction fit
only) and blow into the rubber tubing, using a strong, steady blow rather than a short puff.
Lycopodium dust fills the air in the can and is ignited by the candle. The resulting fire blows the can
lid off.
Safety
Keep your head clear of the top of the can when you blow into the tubing.
Clean Up
Wash the mouthpiece after use. Some lycopodium powder coats the inside of the can instead of
burning. This can be knocked free and collected for reuse.
References
1. A. Alyea and F. Dutton, Tested Demonstrations in Chemistry, 6th Edition, 1965, page 8.
2. Shakhashiri, B. Z., “Chemical Demonstrations”, University of Wisconsin Press, Madison, WI,
Volume 1, Experiment 1.41, pages 103-105.
71
TITLE:
TOPIC:
Dust Explosion
Kinetics
DEMONSTRATION
9.7B
Procedure B. The Flaming Pumpkin
Preparation
Equipment needed:
Fresh pumpkin (or fresh watermelon or ceramic pumpkin), candle, matches,
funnel, rubber tubing, 3/4” × 3” plastic tube (mouthpiece), vinyl tape, transite
sheet.
Chemicals needed:
Lycopodium powder
Carve the pumpkin into a Jack-O-Lantern. Add a small opening low in the back for the rubber
tubing.
Before class, place an unlighted candle inside the pumpkin. Wad a small piece of brown paper towel
and rub it between your hands to form a ball. Place the wad in the bottom of the funnel to minimize
the amount of lycopodium powder that slides down into the rubber tubing. The funnel is in a
weighted base to hold it upright. Fill the bottom third of the funnel with lycopodium powder and put
the funnel inside the pumpkin. Use the vinyl tape to fasten a plastic mouthpiece to the rubber hose,
and place the pumpkin on the transite.
Demonstration
Use a match to light an applicator stick which is long enough to go through the Jack-O-Lantern’s
mouth and light the candle. Blow into the rubber tubing using a strong, steady blow rather than a
short puff. Air rushing through the tube raises a cloud of lycopodium powder, the candle ignites it,
and flame shoots out of the Jack-O-Lantern’s eyes, nose, mouth, and ears.
Safety
Stand several feet behind the Jack-O-Lantern to avoid the flames. Keep any flammable materials
away from the flames.
Clean Up
The pumpkin can survive several flamings over a three day period. After that, the pumpkin is soft
and moldy. It should be wrapped in a plastic trash bag and placed in the dumpster.
References
1. A. Alyea and F. Dutton, Tested Demonstrations in Chemistry, 6th Edition, 1965, page 8.
2. Shakhashiri, B. Z., “Chemical Demonstrations”, University of Wisconsin Press, Madison, WI,
Volume 1, Experiment 1.41, pages 103-105.
72
TITLE:
TOPIC:
Catalytic Decomposition of H2O2
Kinetics
DEMONSTRATION
9.8A
Procedure A. Inflate a Balloon
Preparation
Equipment needed:
1 500-mL filter flask, balloon, fine copper wire, spatula, 100-mL graduate,
#7 solid rubber stopper, #1 one-hole rubber stopper, safety shield, rubber
gloves, insulated gloves.
Chemicals needed:
MnO2, 30% H2O2
Stretch the balloon so that it will inflate relatively easily. Attach the balloon to the side-arm of the
filter flask using a rubber stopper and a piece of fine copper wire. Bend the ends of the wire back so
the balloon is not accidentally punctured as it inflates.
Just before class, add 75 mL of 30% H2O2 to the filter flask and stopper the flask. If the flask is
clean, the H2O2 will not decompose at a significant rate. If oxygen is being given off at a noticeable
rate, empty the flask and clean it thoroughly. Then add the H2O2 and stopper.
Demonstration
Show the class the flask containing the peroxide and the small quantity of oxygen which has been
given off. Open the flask and quickly add one or two spatula’s of MnO2 or a small bag of MnO2
from Demonstration 9.8B. Replace the stopper and set the safety shield in place (between audience
and flask). The reaction begins slowly and as heat is evolved from the exothermic reaction proceeds
more rapidly. Eventually the reaction becomes very rapid and the balloon quickly fills and breaks.
The reaction requires between 5 and 10 minutes; however, it can be speeded up by using a larger
quantity of MnO2.
Note: This demonstration is not very impressive, as written. The balloons that we get do not stretch
easily enough. The balloon only inflates to about 4 inches in diameter and does not break. The
demonstration would be more interesting if a plastic bag was used, as in Demonstration 98.C. And
the Geni in a Bottle, Demonstration 9.8B, is the most impressive version.
Safety
The safety shield is used to protect the audience from any hot H2O2 which might be sprayed about
when the balloon breaks. This is not a very likely event but placing the shield there will certainly
protect them and arouse their interest. Hydrogen peroxide is corrosive to bare skin. The flask gets
hot. Use the insulated gloves when handling the hot flask.
Clean Up and Waste Disposal
The MnO2 bag goes into the waste basket. The solution goes down a sink. The Florence flask is
washed. Any MnO2 stains in the flask are cleaned out with 1 M H2SO4 mixed with a few milliliters
of 30% H2O2. The acid cleaner is neutralized after use.
Reference
H. Alyea and F. Dutton, Tested Demonstrations in Chemistry, 6th Edition, 1965, page 55.
73
TITLE:
TOPIC:
Catalytic Decomposition of H2O2
(Genie in a Bottle)
Kinetics
DEMONSTRATION
(Kit)
9.8B
Procedure B. Genie in a Bottle
Preparation
Equipment provided: 1 L Florence flask, rubber stopper that fits Florence flask (optional), 100 mL
plastic graduated cylinder, Teri towels
Chemicals provided: MnO2 (or MnO2/Fe2O3 mixture) in a Kimwipe bag
Equipment needed:
rubber gloves, insulated gloves
Chemicals needed:
30% H2O2
Cut a Kimwipe in half to make two pieces that are approximately four inches square. Put one piece
on a balance and weigh out 2 g of very fine MnO2, the dust form instead of the granular form. (We
also have a mixture of MnO2 and Fe2O3 that is reactive enough to substitute for pure MnO2.) Form
the Kimwipe into a bag and tie it closed with string. Cut off the excess string and Kimwipe. Put 70
mL of H2O2 in the Florence flask.
Demonstration
Remove the stopper (if used) from the Florence flask and drop the bag of MnO2 into the H2O2. A
plume of vapor begins to emerge and thickens till it is about five feet high or more.
Safety
Hydrogen peroxide is corrosive to bare skin. Use rubber gloves when dispensing H2O2. The flask
gets hot. Use the insulated gloves when handling the hot flask. Keep away from the vapor plume as
it is also hot.
Clean Up and Waste Disposal
The MnO2 bag goes into the waste basket. The solution goes down a sink. The Florence flask is
washed with soap and a brush. Any MnO2 stains remaining in the flask are cleaned out with 1 M
H2SO4 mixed with a few milliliters of 30% H2O2. The acid cleaner is neutralized after use.
74
TITLE:
TOPIC:
Catalytic Decomposition of H2O2
Kinetics
DEMONSTRATION
9.8C
Procedure C. Using Potassium Iodide
Preparation
Chemicals needed:
70 mL 30% H2O2, 5 mL 0.5 M KI
Equipment needed:
1 L Florence flask, 100 mL graduated cylinder, 10 mL graduated cylinder (or
5-10 mL syringe), 1 plastic bag (10 × 8 × 24 inches), rubber bands, goggles,
rubber gloves, insulated gloves.
Measure out the two solutions. Open out the plastic bag so that the folds do not stick together,
allowing it to inflate easily. Then collapse the bag again. Put the rubber bands around the neck of
the plastic bag.
Demonstration
Put the H2O2 in the Florence flask. Put two fingers of one hand inside the neck of the bag through
the rubber bands. use the other hand to pour the KI solution into the Florence flask. using both
hands, pull the rubber bands wide enough to put the neck of the plastic bag over the neck of the
flask. The rubber bands seal the plastic bag to the flask, trapping the gaseous products inside the
bag.
The clear solution in the flask rapidly turns yellow-brown from iodine. The bag begins to inflate
from a mixture of oxygen and steam as the H2O2/KI mixture boils. the bag is fully inflated when the
reaction is complete, and the solution has returned to its original colorless appearance.
(Note: This demonstration does not require a plastic bag, but the reaction does not send up
anywhere near as good a column of steam as when hydrogen peroxide is decomposed with MnO2 in
Demonstration 9.8B, the Genie in a Bottle.)
Safety
Hydrogen peroxide is corrosive to bare skin. Use rubber gloves when dispensing H2O2. The flask
gets hot. Use the insulated gloves when handling the hot flask.
Clean Up and Waste Disposal
The solution can be washed down a sink.
75
TITLE:
TOPIC:
Elephant Toothpaste
(Catalytic Decomposition of Hydrogen Peroxide)
Kinetics
DEMONSTRATION
9.8D
Procedure D
IMPORTANT:
Before performing this demonstration, carefully read the MSDS (Material Safety Data Sheets)
for potassium iodide (KI) and 30% hydrogen peroxide (H2O2). This reaction must be
performed in a large, well-ventilated area with qualified supervision and faculty approval. Do
not attempt to modify the procedure or increase the scale of this reaction. Be sure to wear
safety goggles, gloves, and a lab coat during ALL stages of this demonstration.
Description
When a saturated potassium iodide solution is added to a glass cylinder containing hydrogen
peroxide and dishwashing detergent, a column of steaming bubbles is formed that rapidly overflows
the container.
Preparation
Chemicals needed:
10 mL of 8.6 M aqueous potassium iodide (14.2 g potassium iodide per 10 mL
water), 100 mL of 30% hydrogen peroxide, H2O2, 10 mL of dishwashing
detergent, food coloring.
Equipment needed:
lab coat, rubber gloves, approved safety goggles, 1-L glass cylinder, 10-mL
graduated cylinder, 100-mL graduated cylinder, 250-mL beaker, hot plate,
magnetic stirrer, stir bar, large glass dish, plastic tarp or garbage bag.
Procedure
Put on a lab coat, rubber gloves, and an approved pair of safety goggles. Dissolve 14.2 g of
potassium iodide in 10 mL of water to create a saturated solution (mild heating may be necessary for
complete dissolution, but do not heat strongly). Pour 100 mL of 30% hydrogen peroxide and 10 mL
of dishwashing detergent into a 1-L glass cylinder. Add food coloring if desired, then swirl the
cylinder carefully to mix the contents. Place the cylinder inside a large glass dish centered on top of
a plastic tarp or garbage bag.
To perform this demonstration, pour 10 mL of the saturated potassium iodide solution into the
reaction vessel and stand back. A column of oxygen-filled bubbles will rapidly overflow the
cylinder and pile in and around the glass dish.
76
Hazards
•
•
•
•
The glass cylinder will become very hot. Allow the cylinder to cool before touching it directly,
or use heat resistant gloves.
Potassium iodide can cause skin and eye irritation. Avoid inhalation, ingestion, and contact with
eyes, skin, and clothing. Iodine causes burns and can stain skin and clothing.
30% hydrogen peroxide is a very strong oxidizing agent and may cause severe skin burns.
Contact with combustible materials may cause spontaneous ignition. Store hydrogen peroxide in
a cool, dark area away from reducing agents and organic materials. Do not contaminate the
reagent bottle.
MOST LIKELY ACCIDENT: If the glass cylinder should break, or if large amounts of
hydrogen peroxide should otherwise be spilled, evacuate the area and obtain immediate faculty
assistance.
First-Aid Measures
•
POTASSIUM IODIDE and HYDROGEN PEROXIDE: In case of contact, immediately flush
eyes or skin with copious amounts of water for at least 15 minutes while removing contaminated
clothing and shoes. If inhaled, remove to fresh air. If not breathing, give artificial respiration. If
breathing is difficult, give oxygen. If swallowed, wash out mouth with water provided person is
conscious. Call a physician. Remove and wash contaminated clothing promptly.
Disposal
Much of the foam will settle after a short time. Wearing gloves and a lab coat, transport the reaction
vessel and glass dish to a sink. Carefully rinse the remaining foam down the drain with copious
amounts of water. Do not allow the foam to contact the skin or clothing.
Discussion
The decomposition of hydrogen peroxide is catalyzed by potassium iodide. The rapid production of
oxygen causes the mixture of hydrogen peroxide and dishwashing detergent to foam, rise, and
overflow the reaction vessel. The decomposition reaction is a two-step process:
H2O2(aq) + I–(aq) → H2O(l) + OI–(aq)
(rate determining step)
–
–
H2O2(aq) + OI (aq) → H2O(l) + O2(g) + I (aq)
The presence of oxygen in the foam can be verified by placing a glowing splint into the foam. The
brown color indicates that iodine is present. Iodine can stain clothing and skin, so avoid contact with
the foam. This demonstration is good for introducing topics in chemistry such as kinetics, rate laws,
decomposition, oxidation/reduction, and gas production or limiting reagents.
Reference
http://www.carolina.com/chemistry/experiments/elephant.asp
77
78
TITLE:
TOPIC:
Platinum Catalyzed Oxidation of NH3
Kinetics (chemical reactions)
DEMONSTRATION
(Kit)
9.9
Preparation
Equipment needed:
1 1-liter Erlenmeyer flask with stopper, glass M-rod to fit the flask neck,
platinum gauze on a piece of wire, Meeker burner, flint striker, crucible tongs,
wire gauze pad
Chemicals needed:
100 mL of 15 M aqueous ammonia
Before Class
Pour the ammonia into the flask and stopper.
Demonstration
Unstopper the flask. Hook the platinum gauze’s wire over the M-shaped glass rod. Holding the
platinum gauze with the crucible tongs, heat the platinum to redness in a burner flame. Quickly
insert the platinum into the flask. The platinum hangs from the M-shaped rod which is laid across
the neck of the flask. Dim the room lights so all can see that the platinum continues to glow red.
Comments
This reaction will continue for long periods (up to an hour) unattended if the stopper is left off the
flask. If the flask is stoppered, the reaction quickly dies out.
The products of this reaction are N2 and H2O.
If O2 is blown into the flask, a different reaction occurs. This is the Ostwald process and the
products of the reaction are NO(g) and H2O. Warning: Do not fill the flask with pure O2 for this
demonstration. There will be an explosion.
Safety
Concentrated ammonium hydroxide can cause burns. Ammonia irritates the skin, eyes, and
respiratory system. The platinum remains hot for a while after its removal from the Erlenmeyer
flask. Handle it with the tongs, and let it cool on the wire gauze pad.
Clean Up and Waste Disposal
The ammonium hydroxide is poured into an acid/base waste bottle, neutralized, and washed down a
sink with plenty of water.
References
1. H. Alyea and F. Dutton, Tested Demonstrations in Chemistry, 6th Edition, 1965, page 38.
2. Shakhashiri, B. Z., “Chemical Demonstrations”, University of Wisconsin Press, Madison, WI,
Volume 2 , Experiment 6.26, pages 214-215.
79
TITLE:
TOPIC:
Copper Catalyzed Oxidation
Kinetics (chemical reactions)
DEMONSTRATION
(Kit)
9.10
Preparation
Equipment provided: 1 1-liter Erlenmeyer flask, M-shaped glass rod to fit over the flask’s neck,
copper penny on a wire, Meeker burner, flint striker, crucible tongs, wire
gauze with pad
Chemicals needed:
100 mL of methanol
Demonstration
Place the methanol into the flask before class and cover with Parafilm. Heat the penny to redness in
the burner flame then hang it from the glass rod in the Erlenmeyer flask. Dim the room lights so that
everyone can see the penny glowing red. The product of the oxidation is formaldehyde.
Note: Pennies minted in 1982 and earlier are mostly copper. Pennies minted after 1982 are a
sandwich construction and melt in a burner flame.
Safety
Methanol is a skin irritant, flammable, and toxic if taken internally. The penny is hot even after
losing its red glow. Handle it with crucible tongs, and let it cool on the wire gauze after the
demonstration.
Clean Up and Waste Disposal
Package the methanol for Environmental Health and Safety to pick up. There is a label and waste
manifest on the Demonstration Waste web page.
80
TITLE:
TOPIC:
Reaction Orders, Rate Laws, Visual Estimations
of the Initial Rate of Reaction
2 H+ + H2O2 + 3 I– → I3– + 2 H2O
Kinetics (chemical reactions)
DEMONSTRATION
9.11
Preparation
Equipment needed:
5 - 1 L Berzelius beakers, with large magnetic stirrer bars, magnetic stirrer
with side platform covered with a Teri towel for a white background.
Chemicals needed:
1 M HCl, in graduated cylinders (4-100 mL and 1-200 mL)
0.05 M KI (a 50/500 dilution of 0.5 M stock), in graduated cylinders
(4-50 mL and 1-100 mL)
0.10 M H2O2 (a fresh 5-to-400 dilution of 30%), in graduated cylinders
(3-50 mL and 1-100 mL)
0.001 M KIO3 (1-50 mL portion) (Dilute 5.35 mL of 0.2% KIO3 solution to
50 mL)
Demonstration
In the lecture demonstration, mix the following, one by one, in the order H2O, HCl, H2O2, and
(start timer) KI.
(1) The comparison solution (3.0 × 10–4 M I3–) has:
300 mL H2O, 100 mL HCl, 50 mL KIO3, 50 mL KI
(2)
(3)
(4)
(5)
Volumes
H2O H2O2
300
50
250
100
250
50
200
50
KI
50
50
100
50
HCl
100
100
100
200
Concentrations
[H2O2]
[I–]
1.0 × 10–2 5.0 × 10–3
2.0 × 10–2 5.0 × 10–3
1.0 × 10–2 1.0 × 10–2
1.0 × 10–2 5.0 × 10–3
[H3O+]
0.20
0.20
0.20
0.40
The times for No. 2, 3, 4, and 5 to reach the identical intensity of color as the reference solution (1)
are determined by students in the class using their watches. (Start timing at KI addition.) Since I3– is
so intensely colored, it can be detected at a low concentration, and [I–], [H2O2] remain nearly at their
initial values. Thus this is a determination of the initial rate of reaction, and avoids integration, etc.
Typically (depending on precise concentrations temp, etc.) solution 2 requires 70-80 sec, and each of
the others about half as long.
81
Reaction Orders, Rate Laws, Visual Estimations of the Initial Rate of Reaction
2 H+ + H2O2 + 3 I– → I3– + 2 H2O (continued)
Calculations
Lecturer calculates initial rate in each case, e.g.,:
"[I 3# ] 3.0 x 10#4 M
R2 =
=
= 4.1 × 10–6 M/sec
t2
73 sec
Similarly R3, R4, T5 are all about twice.
Therefore, deduce the rate law:
"[I 3# ]
= k[H2O2]1[I–]1[H+]1
!
"t
Discussion
!
(a) Mechanism, rate-limiting step, SN2 displacement, formation of hypoiodous acid intermediate:
H
H
O
H
(b) Subsequent fast reactions:
O
I
H2O + HOI
HOI + H+ + I– → I2 + H2O
I– + I2 → I3–
Follow-up
Can do same reaction without H+ (or add NH3) and see catalytic decomposition of H2O2. Relate this
to alternative HOI chemistry.
HOI + I– + H+ → I2 (at high [H+])
HOI + H2O2 → O2 + H3O+ + I– (catalyst reagent at low [H+])
Safety
Both the H2O2 and HCl are corrosives. Wear rubber gloves when diluting the 30% H2O2.
82
Reaction Orders, Rate Laws, Visual Estimations of the Initial Rate of Reaction
2 H+ + H2O2 + 3 I– → I3– + 2 H2O (continued)
Waste Disposal
Combine and package the solutions for Environmental Health and Safety to pick up. There is a label
and waste manifest on the Demonstration Waste web page.
If preferred, the waste solutions can be mixed with a little sodium thiosulfate to ionize the iodine.
After the colorless solution is neutralized to a pH of 6-9, it can be flushed down a sink with plenty of
water.
83
TITLE:
Operating Instructions
Corning Catalytic Combustor Demonstration Unit
DEMONSTRATION
9.12
TOPIC:
Show the components of the demonstrator kit and explain.
1.
Enclose portion of a combustor, standard 6000 material. Encased in high temperature glass –
VYCOR®.
2.
Demonstrator unit has a specified path for the gas-flame to get to the combustor.
3.
Propane tank and torch – explanation of propane properties with high ignition temperature
(approximately 1100 ˚F) somewhat difficult to light but with a very high burn temperature
(over 2000 ˚F). It is one of the more difficult of the hydrocarbon groups to be converted in a
catalytic combustor.
Procedures
1.
Light propane torch (moderate, 1-1/2” – 2” long flame)
2.
Insert torch into demonstrator unit.
3.
Heat until combustor leading edge glows (about 1/4”).
4.
Remove torch and cut the flame, leaving the gas supply on, or turn gas off to stop flame, then
turn torn on again for gas with no flame.
5.
Replace torch into combustor demonstrator and allow gas to bring combustor to full glow
with room temperature gas only.
6.
Caution: Stop heating when combustor reaches a red to red-orange glow. Do not continue
supplying gas until very bright to white-orange color is reached, propane can easily generate
temperatures too high for the combustor (over 1800 ˚F).
7.
Note: Glow progresses from leading edge upward.
8.
Remove torch and allow combustor to cool. If this is an instrumented demonstration, drop to
600-700 ˚F if time permits, or 800-900 ˚F to eliminate the glow. If not instrumented, talk
until glow dies out (less than 1000 ˚F).
9.
Reinsert torch with gas on, but no flame.
84
Demonstration 9.12 (continued)
10.
Note: The glow will start in he core or center of the combustor and progress outward to a
full glow. This is proof that it is cool, inlet gas only, providing the fuel for the catalytic
activity to generate the heat. This also proves that the residual temperature of the combustor
is the activation factor to convert (burn) the propane with catalytic assistance.
11.
Bring back to full glow again. Again, use caution and don’t let temperature go too high
(above 1800 ˚F).
12.
This essentially completes the combustor demonstration.
Cautions
1.
Keep propane tank upright or on an angle above horizontal, not flat or with nozzle pointed
downward.
2.
Learn to light propane properly. A match seems easier than the spark/flint type units are
used on acetylene torches, and is in fact a more natural way to demonstrate. The procedure I
use is to turn on the gas and then merely turn it nearly off to get the gas to ignite very gently
in the nozzle. I then turn the gas back up to moderate volume before inserting into the
demonstration unit (use 1-1/2” – 2” flame).
3.
Caution: While building temperature of the catalyst with gas only (no flame), radiant heat
from the catalyst can cause reignition of the gas in the neck of the unit below the catalyst and
reignite the torch as well. This is okay, but it means that you are probably more than hot
enough on the leading edge. You should again partially close gas valve and allow the glow
to propagate more slowly up throughout the catalyst. As in Procedure #6, it may mean that
you have brought the catalyst to full glow and it is time to terminate this part of the
demonstration.
4.
When removing torch with gas not ignited (at the end of the demonstration or at the first
phase when you remove to start the first cooling cycle), accumulated gas with new air supply
in the demonstrating unit can cause flame flashback at the demonstrator’s orifice. This will
be slight and no great concern as long as you are prepared for it to happen.
5.
Keep obvious combustibles away from the demonstration – paper tablecloths, drapes, etc.
6.
The glass tube, demonstrator metal, and the combustor, as well as the torch tip can be very
hot for a considerable time after the demonstration. Be careful!
85
Demonstration 9.12 (continued)
Hints
1.
When cutting the flame, use a flat metal paint scraper or something that will interrupt the
flow of gas for a short period of time to cut the flame path. This will show that the gas is not
adjusted. It may be easier to simply turn gas off until flame goes out, then turn gas back on.
(Some torches do not go out right away, using this method.)
2.
Use a piece of punk to produce smoke or allow cigar or cigarette smoke to flow up through
the still hot but not glowing combustor to show how it is eliminated. This also confirms the
activity below the glowing temperature.
3.
Demonstration is more effective in reduced light.
86
87
88
89
90
91
92
93
94
TITLE:
TOPIC:
The Vapor Pressure of Liquids
Liquids
DEMONSTRATION
(Discontinued)
10.1
Discontinued due to the toxicity of mercury.
Preparation
Equipment needed:
One each of the following per barometer; barometer tube, small Pyrex
crystallizing dish, large Pyrex crystallizing dish, meter stick, ringstand, threefinger clamp, disposable pipet with bent-tip, rubber bulb, black marker.
Chemicals needed:
mercury, suitable liquids for vapor pressure measurement (water, isopropanol,
acetone and diethyl ether work well)
Assemble the required number of Torricelli barometers as follows. Clamp the barometer tube with
the closed end down, resting inside a nested pair of Pyrex crystallizing dishes. Using a disposable
syringe, transfer mercury to the tube to fill it to within 2 to 3 inches of the top. Using a length of
copper wire 1 to 2 feet longer than the tube, chase all the trapped air bubbles out of the mercury,
starting at the bottom and working up. Add enough mercury to fill the tube. Add mercury to the
small crystallizing dish to a depth of 1 to 2 cm. (USE DISPOSABLE GLOVES!) Place your finger
over the open end of the barometer tube and, holding tight to exclude air from the tube, invert the
tube into me mercury pool. Release your finger from the tube under the mercury. Clamp the tube in
a vertical position with the bottom of the tube approximately 1/2 cm above the bottom of the
crystallizing dish. Check the height of the mercury column in the tube. It should be approximately
749 mm above the top of the mercury pool in the dish. If it is not, you have either trapped air in the
tube or your mercury was wet. (A wet mercury column will be about 28 mm lower due to the vapor
pressure of water.) In either case you will need to remake the barometer.
Demonstration
Mark the initial height of the mercury column with a black marker. Add a few drops of the liquid at
the inside base of the barometer tube using a disposable pipet with a bent tip. Avoid transferring air
to the barometer by squeezing the bulb slightly while the pipet tip is under the mercury but outside
the barometer tube. With the addition of the liquid the level of mercury in the tube drops rapidly.
The difference between the old height and the height equals the vapor pressure of the liquid at room
temperature.
Clean Up and Waste Disposal
Carefully pour the mercury from the tube into the dish and transfer the dish to a hood. Use a piece
of filter paper to absorb the excess liquid floating atop the mercury. Allow the mercury to stand
exposed in the hood for an hour to dry. Rinse the tubes well with concentrated nitric acid followed
by distilled water then acetone. Drain well and allow to dry completely before reusing.
95
TITLE:
TOPIC:
Crystal Structure Diffraction
Liquids and Solids
DEMONSTRATION
10.2
Preparation
Equipment needed:
Laser pointer, optical transform slide (in envelope taped to this page in the
Local Demonstration Binder in Gilman 0732)
Demonstration
Shine the laser beam through the diffraction grating slide. Different patterns appear on the wall or
wall screen depending on which part of the optical transform slide is selected.
Safety
Laser light can be injurious if shined directly in someone’s eyes.
96
TITLE:
TOPIC:
Differential Evaporation Rates
Liquids
DEMONSTRATION
10.3
Preparation
Equipment needed:
Ringstand (medium size), aluminum rod 3 or 4 feet long, clamp, brown paper
towels, tape
Chemicals needed:
water, methanol, acetone, ethanol (if desired) in wash bottles or flip top
bottles.
Clamp the aluminum rod at a right angle to the ringstand. Tape the corners of a brown paper towel
to the aluminum rod so that the towel hangs down from the rod. Repeat so that one towel hangs
from the aluminum rod for each reagent.
Demonstration
Squirt each liquid on a separate brown paper towel. The molecular weight and strength of the
intermolecular forces determine the vapor pressure and the rate of evaporation.
Liquids with weaker intermolecular forces evaporate faster than those with stronger intermolecular
forces. Water (H2O, 18 amu = atomic mass units) evaporates slower than acetone (CH3COCH3,
58 amu) because the intermolecular forces are greater in water than acetone. Ethanol (CH3CH2OH3,
46 amu) and methanol (CH3OH, 32 amu) have equal intermolecular forces. In this case, the solvent
with the lower mass evaporates first.
Safety
The organic solvents are irritants and flammable. Avoid getting them on bare skin, do not take them
internally, and keep them away from flames.
Clean Up
The used paper towels can be thrown in a wastebasket after the organic solvents evaporate.
Reference
Gilbert, George L, Dale Dreisbach, Frederic B. Dutton, and Hubert N. Alyea. Tested Demonstrations
in Chemistry. 2 vol., 1994. Experiment C-4.
97
TITLE:
TOPIC:
Reactions of Alkali and Alkaline Earth Metals
with Water
Metals and Metallurgy
DEMONSTRATION
11.1
Preparation
Equipment needed:
2 2-L beakers, two Pyrex crystallizing dishes, forceps, utility knife, glass
plate, paper towels, gloves, goggles, square of window screen
Chemicals needed:
cubes of sodium and potassium 3-5 mm per side, shiny calcium turnings and
shiny magnesium turnings, phenolphthalein, deionized distilled water, sand.
To cut sodium and potassium pieces, put the metal on a glass plate and cut it with a utility knife (or
sharpened spatula or scalpel). The pieces should be no larger than 1/4 cubic centimeter. Store the
sodium and potassium metal in small bottles under mineral oil to minimize oxidation. The calcium
turning should be no larger than the sodium and potassium pieces.
Demonstration
Fill the two beakers about an inch deep with deionized distilled water and add a few drops of
phenolphthalein. Put a piece of sodium in one beaker and a piece of potassium in the second beaker.
Have the class observe carefully the reactions which occur. The sodium reacts vigorously and may
burst into flames. The reaction with potassium is more vigorous yet and almost always burns with a
lavender flame. Put some deionized distilled water and a few drops of phenolphthalein in each of
the small crystallizing dishes. Add a few magnesium turnings to one dish and a calcium turning to
the other dish. Magnesium does not react at a noticeable rate. Calcium reacts at a slower rate than
does sodium or potassium and after a short time yields a milky precipitate, Ca(OH)2. Note that the
solutions have become basic, as shown by the pink color the phenolphthalein.
Note: This demonstration is particularly effective when projected from an overhead projector onto a
screen.
Safety
Use the square of the window screen to cover the large beakers. Use sand to cover any potassium or
sodium that jumps out on the bench. Sodium and potassium are strongly reactive with human skin.
Wear goggles, apron, and gloves when cutting the sodium and potassium. Calcium is less reactive
with human skin, but it should still be handled with forceps, like sodium and potassium.
Clean Up
Either neutralize the solutions or add them to an acid/basic waste bottle for ultimate neutralization.
98
TITLE:
TOPIC:
Sodium in Liquid Ammonia
Metals and Metallurgy
DEMONSTRATION
11.5
Preparation
Equipment needed:
unsilvered Dewar flask, two 1-liter filter flasks, rubber tubing, bent glass
tubing, stoppers, forceps, paper towels, three 3-finger clamps, ringstand
Chemicals needed:
ammonia tank, sodium, 700 mL of 6 M HCl
Assemble the dewar, filter flasks, and hoses as shown in the sketch below. Do this shortly before the
lecture is to begin.
Collect liquid ammonia by inverting the ammonia tank and running a hose from the valve to the
dewar. Sodium metal is cut into the same size pieces as in Demonstration 11.1. The sodium must be
freshly cut as the liquid ammonia cannot cut through an oxidized surface coating.
Demonstration
Remove the stopper from the dewar of liquid ammonia and drop in a piece of freshly cut sodium
metal. The ammonia turns blue as the sodium dissolves. Traces of water and oxygen may make it
necessary to add an additional piece or two of sodium to obtain the blue color.
Use the hood.
Safety
Both liquid ammonia and hydrochloric acid are corrosive. Wear safety gear. Work in a hood during
both preparation and presentation of this demonstration. See Demonstration 11.1 for safety
procedures when working with sodium metal.
Clean Up and Waste Disposal
Remove the stopper from the dewar and allow the ammonia to evaporate in the hood. Wash the
dewar and rinse well with distilled water.
99
TITLE:
TOPIC:
Thermite Reaction
Metals and Metallurgy
DEMONSTRATION
(Kit)
11.10
Preparation
Chemicals provided: Thermite mixture (locked drawer in Gilman 0609), magnesium ribbon, iron
nuggets.
Equipment provided: Two flower pots containing a steel pipe for a crucible, iron ring, clamp, pliers,
crucible tongs
Equipment needed:
ringstand (with steel base), bucket of sand, Transite panels, 3 shields, fire
starter, paper cone, heat-resistant gloves
Thermite formula – 8 parts Fe2O3, 3 parts finely powdered aluminum. About 30 kg of Fe2O3 is stored
in buckets in one of the shelf units under the windows of Gilman 0609. In a large crystallizing dish,
weigh out 800 g of Fe2O3 and 300 g of aluminum and mix well with a spatula. Use a glass dish and
funnel because Fe2O3 sticks to plastic like glue. One batch makes several demonstrations.
Test the firestarter to be sure it works. Take an 8.5 x 11 inch piece of scratch paper. Double it over
twice and cut it into a circle. Make the circle into a cone, which goes into the crucible. Cut 12 inches
of magnesium ribbon, fold it double, and twist it a few times to make the fuse. Put the fuse’s doubled
end in the bottom of the paper cone, and add the thermite mixture until the cone is about half full.
The ringstand, crucible, and sand bucket.
The crucible, thermite and fuse.
At set-up time, put two 2x3 foot Transite panels on the hood end of the bench. The panels protect the
bench top from red-hot iron dust, and the location protects the video camera. Put the ringstand and
sand bucket in the center of the Transite. Hollow out the center of the sand to keep molten iron from
the bucket’s side.
Shields are required to protect the audience. Some lecturers prefer the shields on the floor, for the
lecturer to put in place at demonstration time. Others prefer the shields set up at the beginning of the
period. The shields form three sides of a box, with the open side towards the blackboard. The
shield’s feet interlock so the edges align fairly well.
100
Demonstration
Put the shields up, if this has not been done already. Warn the audience not to look directly at the
burning magnesium ribbon. Light the fire starter and hold the tip of the flame to one of the tips of the
magnesium fuse. As soon as the fuse starts burning, move back to the far corner of the camera
bench. The mixture ignites in a few seconds, producing flame, flying sparks, smoke, and dust.
Molten iron runs down into the sand bath. When the reaction is finished, use tongs to carefully pick
up the red-hot iron (wear heat-protective gloves). Hold it under a stream of water to cool it. Use the
pliers to break up the slag if you wish to recover the iron pieces.
If the reaction fails to ignite, do not attempt to ignite the mixture a second time; instead, discontinue
the demonstration and wait at least five minutes before approaching the reaction vessel.
Safety
Wear goggles and have a fire extinguisher nearby. Clear students out of the first two rows on the
demo side of the room. Use the shields. Warn the students not to look directly at the burning
magnesium fuse. Raise the video screen before lighting the fuse! (A demonstration blooper video
shows a thermite demo setting a screen on fire.)
Waste
Once cooled, the slag and unwanted nuggets of iron can go into a wastebasket.
Reference
Shakhashiri, B. Z. “Chemical Demonstrations”, Volume 1, pages 85-89.
101
TITLE:
TOPIC:
Hydrogen Reduction of Copper(II) Oxide,
“The Copper Crystal”
Metals and Metallurgy
DEMONSTRATION
11.11
Preparation
Equipment needed:
Meeker burner, tripod, transite board with hole in center, copper sample, flint
striker, large glass funnel to fit over the copper, rubber tubing
Chemicals needed:
hydrogen gas
Demonstration
Connect the glass funnel to the hydrogen cylinder with the rubber hose. Make certain the hydrogen
gas is shut off. Light the burner and heat the copper until it is uniformly hot. A black oxide coat
will form during the heating. Turn off the burner and remove it from the area. Start the hydrogen
flowing at a moderate rate so that it fills the funnel. Place the funnel over the hot copper. The black
oxide coating on the copper sample is instantly reduced to metallic copper. Lift the funnel to allow
air to contact the copper, reforming the black oxide. Replace the funnel to reduce the oxide again.
This cycle can be repeated several times before the copper cools if you are quick.
Safety
Hydrogen is flammable. Do not have a flame going when the hydrogen is on.
Burner On and Hydrogen Off
Burner Off and Hydrogen On
Clean Up and Waste Disposal
Return all equipment to storage.
102
TITLE:
TOPIC:
The Oxidation States of Vanadium
Metals and Metallurgy
DEMONSTRATION
(Kit)
11.12
Preparation
Equipment needed:
test tube rack
Chemicals provided: sealed ampules of VO2+, VO2+, V2+
Demonstration
The solutions in the ampules are yellow (VO2+), green (VO2+), and violet (V2+).
103
TITLE:
TOPIC:
The Hydrolysis of Titanium Tetrachloride,
“Skywriting”
Metals and Metallurgy
DEMONSTRATION
11.13
Preparation
Equipment needed:
cotton-tipped applicator sticks
Chemicals needed:
TiCl4
Demonstration
Dip the cotton-tipped applicator stick into the bottle of TiCl4 solution then wave the stick through the
air. Hydrolysis with moisture in the air produces a white smoke of Ti(OH)4.
Note: The air must be reasonably moist (it almost always is in Ames) for this to work well. Test if
in doubt.
Clean Up and Waste Disposal
Put the applicator stick(s) in a plastic bag and drop the bag in a dumpster. Save the bottle of TiCl4.
104
TITLE:
TOPIC:
Halogen Train”
Non-Metals
DEMONSTRATION
12.3
Suggested Application: The halogens; the relative strengths of the halogens as oxidizing agents; the
halogen displacement series.
Preparation
Equipment needed:
1-L Florence flask*
dropping funnel or long stem separatory funnel*
2-hole stopper*
right-angle bend 8-mm*
glass tube ~ 25-mm diam., 60 cm long
2-1-hole stoppers (to fit the 25-mm diam. tube)
glass tubing (bent as shown in the diagram)
rubber tubing
2-1 L filter flask
2 ringstands, 2 clamps, 1 iron ring
3-three finger clamp, each with a ringstand clamp
Crescent wrench (to open the chlorine lecture bottle valve)
Chemicals needed:
MnO2*
12 M HCl*
1 M KBr solution
1 M KI solution
3 M NaOH
glass wool or cotton
* – these items may be omitted if a lecture bottle of chlorine is used. Use a Cl2 lecture bottle, if
possible.
105
Halogen Train (continued)
Moisten glass wool or cotton in KBr solution.
Insert this in the glass tube at a point nearest the
Cl2 generator. Moisten another glass wool or
cotton “plug” with KI solution and insert in the
other end of the tube. [Keep the tube clamped in a
horizontal position while doing this so the
solutions do not run together. Do not pack the
“plug” so tightly that the smooth passage of gas is
inhibited!]
Insert stoppers. Connect the “KBr-end” of the tube
to the Cl2 generator and the other end of the tube to
some rubber tubing which is submerged in a baker
of NaOH solution
Demonstration
Begin to generate Cl2 gas by allowing portions of the HCl to come in contact with the MnO2. [To
prevent the gas from coming back through the dropping funnel, add a small amount of water to the
flask sufficient to cover the tip of the inlet tube.] Warming may be necessary.
The evolution of light green Cl2 gas should be observed. As the gas comes in contact with the KBr
“plug” the brown color of Br2 appears. A mixture of green Cl2 and brown Br2 vapors are observed
passing through the tube until the KI “plug” is reached. At this point, purple I2 is deposited. Any
excess Cl2 is absorbed in the NaOH at the end of the train.
Comments
Based on observations, students should be asked to write balanced equations for all the reactions.
The reactions are:
MnO2 + 4 HCl → MnCl2 + 2 H2O + Cl2
Cl2 + 2 Br– → Br2 + 2 Cl–
Br2– + 2 I– → I2 + 2 Br–
Cl2 + 2 I– → I2 + 2 Cl–
Cl2 + 2 NaOH → NaOCl + NaCl + H2O
Br2 + 2 NaOH → NaOBr + NaBr + H2O
Ask students what they might expect with F2 instead of Cl2.
Safety
Chlorine gas is toxic. Prepare and tear down this demonstration in a hood! Do not generate the Cl2
too fast as it may bubble out of the NaOH solution before it has had the opportunity to react.
106
Halogen Train (continued)
Waste Disposal
Add the bromine and iodine soaked glass wool to a gray tub of sodium thiosulfate solution. This
ionizes the halogens. Discard the glass wool in a wastebasket.
Mix the sodium hydroxide/sodium hypochlorite solution with sodium thiosulfate. Neutralize the
sodium hydroxide, and wash all the waste solutions down a sink with plenty of water. Work in a
hood!
Reference
Hutton, W. M., “My Favorite Lecture Demonstrations”, pages 15-16.
107
TITLE:
TOPIC:
Sublimation of Iodine
Non-Metals
DEMONSTRATION
Equipment needed:
ringstand, clamps, heat gun or Bunsen burner
Chemicals needed:
sealed tube of iodine from Demonstration 12.2, the halogen display
12.5
Preparation
Clamp the iodine tube to a ringstand. Before lecture heat the upper portion of the tube with a gentle,
lazy flame from a Bunsen burner to return all iodine to the bottom of the tube. Allow to cool.
Demonstration
Heat the iodine gently and observe the purple vapor and the growth of crystals of iodine on the upper
walls of the tube.
108
TITLE:
TOPIC:
Nitrogen Oxides and Nitric Acid
Non-Metals
DEMONSTRATION
Equipment needed:
crystallizing dish
2-12 inch high reaction cylinder,
ringstand with two finger clamp and iron ring
balloon
36 inch rubber hose
3-3 in × 3 in right angle bend glass tubing
3 inch glass tubing with a #1 one-hole rubber stopper
pinch clamp
rubber stopper to fit the reaction cylinder
hose bib or lecture bench water faucet
Chemicals needed:
Water
NO gas
oxygen gas
1 M NaOH
methyl red indicator
12.14
Note: See Shakhashiri, Vol. 1, Demonstration 1.44, page 117 for the preparation of NO gas.
Preparation
Fill the crystallizing dish half full and the reaction cylinder totally full of water. Stopper the
cylinder, and invert it in the crystallizing dish. As little air as possible should be trapped in the
cylinder. Add about 10 mL of 1 M NaOH and a sufficient quantity of methyl red to the water.
Allow at least one hour for preparation for the NO gas, if it is not available in a gas cylinder. Fill the
top 1/3 of the inverted reaction cylinder with NO. Swirl the cylinder to mix the water and neutralize
the HNO3 formed in the production of NO gas.
Fit the right angle bend glass tubing into one end of the rubber hose. Fit the other end of the hose to
the three inch glass tube with the rubber stopper, which goes into the neck of the balloon. Fill the
balloon with pure oxygen and clamp the rubber hose with the pinch clamp. Put the balloon in the
iron ring on the ringstand.
Demonstration
Put the free end of the hose from the balloon into the inverted reaction cylinder. Open the pinch
clamp wide for one second. Immediately remove the hose and lower the cylinder so that its mouth is
flat on the bottom of the crystallizing dish.
109
Nitrogen Oxides and Nitric Acid (continued)
Oxygen and NO gas combine to make brown NO2 gas, which is soluble and reacts with water to
form HNO3. Properly done, all the gas dissolves. Water moves up in the cylinder from atmospheric
pressure. As water moves into the cylinder, a little HNO3 moves out to the dish. The acid turns the
methyl red in the cylinder pink while the water in the dish stays less acidic and yellow in color.
Waste Disposal
Neutralize the acid, and flush it down a sink.
Reference
Modified from Gillespie et. al., Chemistry, 1st edition, experiment 17.2, page 628.
110
TITLE:
TOPIC:
Preparation of Silane, SiH4
Non-Metals
DEMONSTRATION
12.15
Preparation
Chemicals needed:
Magnesium powder (At. Wt. 24.31) (40 80 mesh, shiny, unoxidized)
Sea sand (very fine, FW 60.09) dried in an oven night
3 M HCl
Materials needed:
Meker burner
16 × 150 mm test tube (pyrex)
250 mL beaker
aluminum rod with clamp
Dry some fine silica sand in a drying oven overnight. Moisture in the sand causes unwanted burps
during heating in class. Add 5 g of the sand to 4 g of magnesium and mix well. This will fill about
one third of the test tube.
Demonstration
Fill the beaker about half full of 3 M HCl. Heat the sand and magnesium mixture in the Meker
burner flame until the mixture is red hot. The mixture now contains Mg2Si. Remove the tube from
the flame, and let it cool. Pour the Mg2Si into the 3 M HCl or crush the end of the tube with pliers
so that the Mg2Si (and broken glass) fall into the 3 M HCl. Bubbles of silane gas (SiH4) rise to the
surface. The bubbles react spontaneously with air, causing a series of clearly audible pops.
Clean Up and Waste Disposal
The glass and the associated slag are discarded in the broken glass bin. The acid is neutralized to a
pH of 6-9 and flushed down the sink. Any other solid waste goes in the wastebasket.
Reference
Gillespie, Ronald J., David A. Humphreys, N. Colin Baird, Edward A. Robinson. Chemistry.
Allyn and Bacon, Inc., Boston. 1986. Experiment 21.11, p. 768.
111
TITLE:
TOPIC:
Radioactive Minerals
Nuclear Chemistry
DEMONSTRATION
(Kit)
13.1
Preparation
Equipment provided: Radiation count rate meter with probe, radioactive mineral samples,
evaporating dish with uranium glaze.
Demonstration
Follow directions below (and on the top of the meter) to set the rate meter up for use. Remove the
red protective cap from the end of the probe. The meter clicks when the probe is near a source of
radiation.
Directions for Operating the Model 800 Radiation Count Rate Meter
CAUTION — Before turning on the radiation count meter, make sure the High Voltage control is in
the fully counter clockwise position. Excess high voltage can damage the Geiger Mueller tube.
1. Set controls in the following position prior to initial turn on:
(a) Audio Monitor — fully clockwise
(b) Range CPM — X10
(c) High Voltage — fully counter clockwise
(d) Audio Push Button — in for On
(e) Meter Push Button — out for High Voltage
2. Turn on unit by the on-off push button
3. Slowly advance high voltage control, being careful not to exceed 700 volts at this time. You
should now hear an occasional popping from the speaker. This is background radiation, and you
are now ready to run your experiments. Typically the tube should operate in the 500 to 600 volt
range.
4. Turn the High Voltage control back to zero before turning the unit off.
112
TITLE:
TOPIC:
Chain Reaction Simulation
Nuclear Chemistry
DEMONSTRATION
(Kit)
13.2
Equipment provided: 49 mousetraps, 98 corks, 4 #13-1/2 solid rubber stoppers, 1 #6 one-hole
rubber stopper
Equipment needed:
plywood base (Gilman 0162)
plexiglas cover (Gilman 0162)
Chemicals needed:
none
Preparation
Obtain 4 large rubber stoppers and place them at the corners of a rectangle slightly smaller than the
plywood base. Place the plywood base on the stoppers to help isolate it from vibrations. Set the
traps in a regular array on the base, taking care to allow room to place the top over the set traps. The
ISU version uses 49 mousetraps in seven rows and seven columns. Set them so that the mousetraps
in each column are oriented in the same direction. The traps in each column should be oriented
opposite to the orientation of the adjacent columns. Place a cork on each corner of the trap wire, two
corks per trap. When the traps and corks are in place, carefully lower the plexiglas cover over the
traps.
Three columns of two mousetraps,
showing the placement of the corks.
The demonstration, ready for use.
Demonstration
Place four large stoppers on the lecture bench at the corners of a rectangle a little smaller than the
plywood base. With an assistant, carefully carry the unit to the lecture table and place it on the
rubber stoppers. Drop a rubber stopper (#5 or #6) through the hole in the plexiglas top so that it
strikes a trap below. Nearly all the traps will go off within a second as the flying corks strike them.
Clean Up and Waste Disposal
Spring any unsprung traps. Replace the corks, rubber stoppers, and mousetraps in the kit. Repair or
replace any damaged traps.
113
TITLE:
TOPIC:
Production of Ethylene by Dehydration of Ethanol
Organic Chemistry
DEMONSTRATION
14.1
Preparation
Equipment needed:
1-liter Erlenmeyer flask, 200-mL round-bottom flask, #4 1-hole rubber
stopper, bent glass tubing, rubber tubing, plastic pan, burner, ringstand,
gloves, goggles, apron, #8 solid rubber stopper, 3-finger clamp
Chemicals needed:
20 mL of absolute ethanol, 50 mL of concentrated sulfuric acid, boiling stones
Set up the equipment as shown in the sketch. Add 20 mL of absolute ethanol and a few boiling
stones to the round-bottom flask. Carefully add the 50 mL of the 18 M H2SO4, swirling often to
thoroughly mix the ethanol and acid. CAUTION! The flask will get quite hot.
Demonstration
Heat the round-bottom flask gently until the ethylene gas comes off at a rate of about 500 mL per
minute. Collect the gas until the flask is 2/3 to 3/4 full then shut off the burner and allow the
reaction to subside.
Safety
WARNING! Failure to extinguish the burner flame can result in a fire if the flask fills with ethylene
and the excess vapors spill out into the room. Use the lecture bench exhaust vent!
The H2SO4 is a corrosive! Do not allow it to touch bare skin.
Waste Disposal
Discard the ethylene gas in a hood. Neutralize the sulfuric acid/ethanol mixture and flush it down a
sink with plenty of water.
114
TITLE:
TOPIC:
Production of Acetylene by the Reaction of
Calcium Carbide and Water
Organic Chemistry
DEMONSTRATION
14.2
Procedure A. Collection of Acetylene
Equipment needed:
1-liter Erlenmeyer flask, 125-mL Erlenmeyer flask, #5 2-hole rubber stopper,
bent glass tubing, rubber tubing, plastic pan, gloves, goggles, apron, ringstand,
thistle tube
Chemicals needed:
3 g of calcium carbide (fresh!)
Preparation
Set up the equipment as shown in the sketch. Add 3 g of calcium carbide to the 125-mL Erlenmeyer
flask and stopper. Adjust the thistle tube so the end just clears the bottom of the flask.
Demonstration
Pour 50 mL of water into the thistle tube and collect the evolved acetylene in the large flask.
Waste Disposal
Put the wet calcium carbide in a hood until acetylene production is complete. Either neutralize the
resulting calcium hydroxide or add it to an acid/base waste bottle for eventual neutralization or
package it for pick up by Environmental Health and Safety.
115
Production of Acetylene by the Reaction of Calcium Carbide and Water (continued)
Procedure B. Calcium Carbide Explosion (Kit)
Equipment provided: Iron base of a ring stand (or metal sheet about 30 cm × 30 cm)
Tin can (with the bottom removed, a 1-2 mm hole cut in the top), and 4 holes,
each 1/4 inch diameter, cut in the side close to the open bottom.
Matches
Bench paper (approximately 1/2 meter square)
Craft stick (popsicle stick)
Rubber bands or twist ties
Chemicals provided: 0.8-1.0 g Calcium carbide (lumps)
Equipment needed:
Aluminum rod approximately 1 m long
Chemicals needed:
Water in a wash or dropper bottle
Preparation
Fasten the craft stick (or an applicator stick) to the end of an aluminum rod with rubber bands or
twist ties. Light the end of the craft stick and let it burn for a few seconds to char the end. A charred
end is easier to light at the demonstration than an uncharred end.
Demonstration
Three or four calcium carbide lumps are set in a group on the ring stand base. They are sprayed with
water from the wash bottle. The can is put over the calcium carbide. Acetylene evolves from the
wet calcium carbide and escapes through the hole in the top of the can. Wait about 15-20 seconds.
Light the craft stick, and touch the flame to the hole in the top of the can. The acetylene explodes,
sending the can leaping into the air.
Safety
Use only 1 g of calcium carbide in this demonstration. More calcium carbide produces more
acetylene, which forms a gas mixture that is lower in oxygen than desired, which makes a weaker
BANG when ignited.
Waste Disposal
Put the wet calcium carbide in a hood until acetylene production is complete. Either neutralize the
resulting calcium hydroxide or add it to an acid/base waste bottle for eventual neutralization or
package it for pick up by Environmental Health and Safety.
116
Production of Acetylene by the Reaction of Calcium Carbide and Water (continued)
Procedure C. Calcium Carbide Sock Shooter
Preparation
Equipment needed:
sock shooter, wadded sock, #6 plastic medicine dropper, ~30 mL widemouthed bottle; Tesla coil or fire lighter, ringstand with three-finger clamp.
Chemicals needed:
0.8 g calcium carbide, water
Construction: The sock shooter is made of an 18 inch length of 2 inch diameter PVC pipe, a 2 inch
female adapter PVC fitting (ISU Central Stores 7608.5161), and a 2 inch threaded PVC cap (ISU
Central Stores 7608.1751 ??) to fit the female adapter. The touch hole is a 1/8 inch diameter hole
drilled in at a 45 degree angle starting where the female adapter is glued to the barrel and pointing
inwards toward the screw cap. If a Tesla coil will be used, drill holes for two screws. The holes are
on opposite sites of the barrel and 7-8 inches from the shooter’s breech end. These holes should be
offset ¼ to ½ inch so that when a screw is in each hole, there is a gap for a spark to jump across.
Weigh out 0.8 gram of calcium carbide lumps and place it in the bottle. This produces an excellent
BANG, while more than 1 g of CaC2 generates too much acetylene gas and makes the shooter hard
to light off. For convenience, clamp the sock shooter in a ringstand at a 45 degree angle. Fill the
medicine dropper with water and dry the tip. Stuff the wadded sock in the sock shooter's muzzle.
Just before the lecture, unscrew the threaded cap on the breech end of the sock shooter, put the
calcium carbide in the square recess in the cap, and screw the cap back on. Insert the dropper of
water through the touch hole into the cavity in the breech cap where the calcium carbide is located.
Demonstration
Point the sock shooter towards the side of the room and upward at a 45 degree angle. Squeeze the
medicine dropper to force the water into the cavity in the breech cap. The water reacts with the
calcium carbide to produce acetylene, which forms an explosive mixture with air. Wait 5 seconds in
order to get a good amount of acetylene. Either touch the Tesla coil to a screw or apply flame from
the fire lighter to the touch hole. There is a loud BANG, and the sock flies 20 feet or more.
Safety
Give a noise warning because the sock shooter is quite loud. Take care not to zap anyone with the
Tesla coil or to burn anyone with the fire starter.
Waste Disposal
Put the wet calcium carbide in a hood until acetylene production is complete. Either neutralize the
resulting calcium hydroxide or add it to an acid/base waste bottle for eventual neutralization or
package it for pick up by Environmental Health and Safety.
117
Demonstration 14.2C: Calcium Carbide Sock Shooter
The sock shooter should be clamped in a ringstand, with a sock in the end. The #6 plastic dropper
should be full of water, and some calcium carbide should be in the shooter’s breach end.
Demonstration Steps:
1. Screw the breach with the CaC2 into the shooter barrel.
2. Insert the plastic dropper through the touch hole.
3. Tilt the shooter to a 45 degree angle and pint it at a wall.
4. Squeeze the plastic dropper to squirt water on the calcium carbide.
5. Take the dropper out of the shooter.
6. Wait 10 seconds (the students can do a countdown)
7. Zap a screw with the Tesla coil.
8. BANG!
118
TITLE:
TOPIC:
Bromination of Unsaturated Hydrocarbon Gases
Organic Chemistry
DEMONSTRATION
14.3
Preparation
Equipment needed:
250 mL Erlenmeyer flask, reaction cylinder (or 1/2 L-1L clear glass bottle),
3” × 3” #6 right angle bend glass tubing, #6, 1-hole rubber stopper, 100 mL
beaker, Parafilm, frit, 18” rubber tube
Chemicals needed:
CaC2, methylene chloride (dichloromethane), Br2, water
Fill the reaction cylinder around half full of methylene chloride. Add 3-4 drops of Br2, shake and
cover the cylinder with Parafilm. Put around 6 g CaC2 in a 250 mL Erlenmeyer flask and stopper.
Connect frit to rubber tubing to right angle glass bend in #6 stopper. Put around 60 mL H2O in
beakers and cover it with parafilm.
Demonstration
Uncover the reaction cylinder and put the frit in it. Uncover the Erlenmeyer flask and add the water
to the CaC2 to generate acetylene as in Demonstration 14.2A. Put the stopper in the flask. Hold the
stopper in place to prevent the gas pressure from blowing off the stopper.
Acetylene is formed, goes through the tube and the frit and becomes brominated. The solution
slowly loses its color as the bromine reacts with the acetylene. The reaction takes about 5 minutes to
complete. HOOD!
Waste Disposal
Package the waste for Environmental Health and Safety to pick up. A waste label is on the
demonstration waste web site.
119
TITLE:
TOPIC:
The Methane Mamba
Organic Chemistry
DEMONSTRATION
(Kit)
14.4
Methane gas is bubbled up through a funnel of soapy water and a buoyant column of suds grows
gracefully upward like a large bubbly snake swaying elegantly to the air currents in the room.
Igniting this methane mamba provides for a rather charming effect!
Not Recommended for Gilman 1352, 1652, and 1810.
Chemical Concepts:
1. Whether an object floats or sinks in a fluid depends on whether that object’s density is less than
or greater than the density of the fluid. This holds true for objects submerged in liquids as well
as gases.
2. For gases under similar conditions, densities are essentially proportional to molecular weights.
3. Hydrocarbons are generally combustible – that is, they react exothermically with oxygen. The
products are usually CO2 and H2O.
Materials:
source of natural gas
*funnel (made from the top half of a 2-L plastic soda bottle)
#5 1-hole rubber stopper
glass tubing (6 mm diam) to fit stopper, 9 cm long
rubber hose to fit gas jet nozzle, approx. 1 m long
ring stand and large iron ring support (5 in. diam)
test tube clamp
candle taped securely to the end of a meter stick
* The ISU Chemistry Club has a funnel made from a crystallizing dish. A plastic soda bottle will
burn when the bubble column is ignited.
Construction:
1. Carefully, and with adequate lubrication, slide the rubber stopper over the glass tube to about the
midsection. Then insert the stopper securely into the mouth of the funnel.
2. Connect the protruding end of the glass tubing to the rubber hose. If the fit is too loose, wrap the
end of the tube with some electrician’s tape to make the hose fit more snugly.
3. Use the ring stand, camp and large ring support to secure the funnel in a vertical position,
stoppered end down. Run the hose up over the neck of the ring support (to avoid leakback) and
then connect it to the gas jet.
Procedure:
1. Pour 300 mL of soap solution (3% Dawn® by volume) into the funnel. The top of the glass
tubing should be submerged by about 1.5 cm. (See Figure 1 on the following page.)
120
2. Begin the snake charming music (if available!). Then, with no open flames nearby, turn on the
gas jet full throttle. A column of methane bubbles will begin to grow upward, attaining a height
of 2-3 meters in about 5 minutes. (Note: The ISU Chemistry Club grows the column of bubbles
up a rod. This minimizes the chance that the bubble column will break off and float away.)
Discussion:
Methane is about half as dense as air. You can approximate this by comparing their relative
molecular weights: CH4 (mw = 16) compared to air, a mixture of N2 (mw = 28) and O2 (mw = 32).
Because of its lower density, pure methane rises rather rapidly in air. The soapy water adds
significantly to the density, but with just the right proportions, as described below, you can achieve a
soapy water/methane mixture that is just slightly less dense than the surrounding air, and that
ascends very slowly. The adhesive nature of the soapy water, due mostly to the H-bonding that
occurs between the water molecules, helps to hold adjacent bubbles (suds) together in a snake-like
cluster.
Tips:
1. If there are too many large bubbles, the column will be too buoyant and will tend to pinch off
before reaching its full height. If there are too many small bubbles (suds), the column will be too
dense and will simply spill over the rim of the funnel. The best results are obtained from a
combination of large and small bubbles, producing a column that is just barely less dense than air
– enough to support its own weight but not cause a substantial upward tug. This might require
some ‘fine tuning” – adjusting the flow rate of the methane, the position of the glass tubing and
the depth of the soapy water in the funnel. Humidity may also play a role, for the top of the
column does tend to dry out.
2. An interesting effect can be achieved by placing a few drops of water on the top of the growing
column. Since the water increases the density, it causes the top to arch over – accentuating . . .
121
TITLE:
TOPIC:
The Gelation of Poly(vinyl alcohol) with Borax,
“Slime”
Polymer Chemistry
DEMONSTRATION
15.6
See the reference. A photocopy follows this page.
Preparation
Equipment needed:
Tray, 50-mL graduated cylinder, 50 mL plastic syringe, craft stick, paper or
plastic 3 oz. cup, waste container
Chemicals needed:
2% (or 4%) poly(vinyl alcohol) solution 4% borax (w/w)
Borax is sodium borate decahydrate (Na2B4O7•10H2O)
When using MW 124,000-186,000 poly(vinyl alcohol), use a 2% solution instead of a 4% solution.
Lower molecular weight PVA requires the higher concentration.
Poly(vinyl alcohol) does not dissolve easily. Add 10%-20% of the total quantity to vigorously
stirred water. Let stir for a minute or two and repeat with another 10%-20% . Continue until all the
PVA is in the water. This minimizes the likelihood that the PVA grains will stick together. The
undissolved granules must be stirred vigorously for at least one hour (overnight is better) to hydrate
them before heating. The solution must be heated to 90-95˚C for 30-60 minutes or until the solution
becomes clear. After cooling, the solution can be stored in a refrigerator for several months before
bacterial growth makes it useless.
Waste Disposal
The gel can be collected in a plastic bag and discarded in the dumpster. Solutions can be washed
down a sink with plenty of water.
Reference
Casassa, E. Z., Sarquis, A. M., and Van Dyke, C. H., 1986, “The Gelation of Polyvinyl Alcohol with
Borax”, J. Chem. Ed. 63(1): 57-60.
Sarquis, A. M., 1986, “Dramatization of Polymeric Bonding Using Slime”, J. Chem. Ed., 63(1):
60-61.
122
123
124
125
126
127
TITLE:
TOPIC:
Disappearing Styrofoam
Polymer Chemistry
DEMONSTRATION
15.7
Preparation
Equipment needed:
Disposable paper cup, approximately 7 oz. capacity, 600 mL glass beaker
Chemicals needed:
Acetone, rod of styrofoam approximately 2 × 1-1/2 × 12 inches
Cut the styrofoam to the desired dimensions. Chemistry Stores usually has styrofoam to give away.
Demonstration
Fill the paper cup about 1/4 full of acetone and put the paper cup in the beaker for stability. Put one
end of the styrofoam in the acetone and gently press down. The styrofoam turns into a gooey sludge.
A relatively small amount of material is left, showing how much gas had been trapped in the
syrofoam.
Clean Up and Waste Disposal
Allow the acetone to evaporate in the hood. Discard the cup and styrofoam residue in the dumpster.
128
TITLE:
TOPIC:
Happy and Sad Balls
Polymers
DEMONSTRATION
(Kit)
15.8
Preparation
Equipment needed:
Happy and Sad Ball kit containing two polymer balls that are one inch in
diameter. (Location: 0162 Gilman, cabinet 0162-2, top shelf.)
Chemicals needed:
None required.
Demonstration
Drop the two balls from an equal height to a hard surface. The happy ball bounces to approximately
a quarter of the height it was dropped from. The sad ball bounces an inch or so.
The happy ball is made of natural rubber. The sad ball is made of polynorbornene, which has low
restitution elasticity and very good energy absorption. It can absorb high frequency vibrations in
addition to dampening impacts.
Safety and Waste Disposal
None.
129
TITLE:
TOPIC:
The Blue Bottle
Redox Chemistry
DEMONSTRATION
16.10
Preparation
Equipment needed:
500 mL Florence flask
rubber stopper to fit flask
250 mL plastic bottle with cap
Chemicals needed:
150 mL 1 M potassium hydroxide
150 mL ~0.4 M dextrose (glucose) (10 g/150 mL H2O)
1% methylene blue (or 0.1% resazurin or 0.5% indigo carmine)
Put the potassium hydroxide in the plastic bottle and the glucose solution in the Florence flask.
Approximately five minutes before class, pour the potassium hydroxide into the Florence flask and
swirl. Add 6-8 drops of methylene blue, swirl the solution, and stopper the flask. The solution
becomes blue and soon fades to clear upon standing.
Demonstration
Shaking the solution causes it to turn blue. The solution becomes clear again after standing for about
a minute. The cycle repeats whenever the flask is shaken.
Variations: There are similar redox reactions using ~0.1% resazurin (clear to red) or ~0.5% indigo
carmine (yellow to green). See Bodner, et. al., Demonstration 18.1. An advantage of using
resazurin is that the stock solution has a longer shelf life than methylene blue.
Safety
Sodium hydroxide is a corrosive.
Waste Disposal
Neutralize the solution to a pH of 6-9, and flush it down a sink with plenty of water.
References
Bodner, George M., Kurt L. Keyes, Thomas J. Greenbowe. The Purdue University lecture
demonstration manual. John Wiley & Sons, New York. 1989, 176 pp. Demonstration 18.1.
Gilbert, George L., Hubert N. Alyea, Frederic B. Dutton, Dale Dreisbach. Tested demonstrations in
chemistry. 1994, 2 vol. Demonstrations G-6, G-7, G-8.
130
131
132
TITLE:
TOPIC:
Unsaturated, Saturated, and Supersaturated
Sodium Acetate Solutions
Solutions
DEMONSTRATION
(Kit)
17.1
Preparation
Chemicals provided: sodium acetate trihydrate, one saturated solution of sodium acetate, one
supersaturated solution of sodium acetate. Additional flasks of supersaturated
solution are available in Gilman 0162.
Equipment needed:
Parafilm (0732) (for clean up), 1-250 mL beaker (0732) (for clean up)
Chemicals needed:
1 unsaturated solution of sodium acetate (equals distilled water) in a 2L
Florence flask
Saturated and supersaturated solutions of sodium acetate are probably on hand. If they must be
prepared from scratch, prepare as follows:
Saturated sodium acetate: 1300 g of sodium acetate trihydrate per liter, heat till dissolved, and allow
to cool. A cool solution will not hold as much sodium acetate in solution as a hot solution. If
necessary, add some more sodium acetate trihydrate for a good layer of crystal.
Supersaturated sodium acetate: Heat (without boiling) the sodium acetate trihydrate in a flask
covered with a beaker until all the sodium acetate has gone into solution in the water of hydration. .
After all the solid has melted, allow the flask to cool, while covered with the beaker, to room
temperature. The sodium acetate should remain liquid, but it may solidify if a few seed crystals
remain in the flask's neck. To store the supersaturated solution, cover the flask with a piece of
Parafilm. This solution can be kept in a cabinet indefinitely and used repeatedly.
Demonstration
Obtain some sodium acetate trihydrate crystals in your hand and add some to the unsaturated sodium
acetate solution to show that the solid dissolves readily. Now add some to the saturated solution to
show that no additional sodium acetate can be dissolved in this solution. Take the flask containing
the supersaturated sodium acetate solution and shake it to see if this unstable solution will
crystallize. If it does not, remove the Parafilm and snap your fingers over the mouth of the flask
several times. (This should dislodge some small crystals of sodium acetate from your hands, causing
them to fall into the supersaturated solution.) Explain to your students what happened when you
snapped your fingers over the flask.
Clean Up and Waste Disposal
The flask of saturated sodium acetate is covered with Parafilm and stored. The flask containing the
unsaturated solution is emptied and cleaned. The flask containing the now solidified supersaturated
sodium acetate solution is heated, with a beaker over the neck to prevent the loss of water. A few
milliliters of water may need to be added every few heatings. After the solid has all gone into
solution, allow the flask to cool to room temperature and then cover with Parafilm and store until
needed again.
Reference
Shakhashiri, B. Z., “Chemical Demonstrations”, University of Wisconsin Press, Madison, WI,
Vol. 1, Experiment 1.11, pages 27-30.
133
134
TITLE:
TOPIC:
Vapor Pressure Lowering
Solutions
DEMONSTRATION
(Discontinued)
17.3
Discontinued due to the toxicity of mercury.
Preparation
Equipment needed:
3 barometer tubes, meter stick, 3 small Pyrex crystallizing dishes, 3 large
Pyrex crystallizing dishes, length of copper wire 1 to 2 feet longer than the
barometer tubes, syringe, 3 bent-tip disposable pipets, 3 sample bottles
Chemicals needed:
diethyl ether, t-butanol
The barometers are set up as per the instructions in Demonstration 10.1. Fill and label the sample
bottles of pure t-butanol and diethyl ether. A solution of t butanol in diethyl ether with a mole
fraction of t-butanol of 0.25 is prepared by dissolving 10 mL of t-butanol (MW = 74.12 g;
d = 0.789 g/mL) in 33.2 mL of diethyl ether (MW = 74.12 g; d = 0.714 g/mL). Use pipets for
measuring out the reagents for the mixture.
Demonstration
The initial height of the mercury column above the pool is measured to obtain the prevailing
atmospheric pressure, Patm. A few drops of the liquids or the solutions are added to a column and the
height of the mercury column is again measured. These new heights are subtracted from Patm to
obtain Pt butanol, Pether, and Psolution.
Raoult’s Law may be verified by comparing the predicted pressure of the solution
(Psolution = Nt-BuPot-Bu + NEtPoEt) with the pressure measured.
Typical Data
Patm
_______________
ht-Bu
_______________
Pot-Bu
_______________
hEt
_______________
PoEt
_______________
hsolution _______________
Psolution _______________
Psolution(cal’c) = 0.25 (Pot-Bu) + 0.75 (PoEt) = _______________
135
TITLE:
TOPIC:
Osmotic Pressure
Solutions
DEMONSTRATION
(Kit)
17.4
Preparation
Equipment provided: dialysis tubing, double buret clamp, 1 L Berzelius beaker (or substitute a 101/2 × 4 in reaction cylinder), small funnel, #1 one-hole rubber stopper,
Spectra/Por weighted closures, small rubber bands, marker (such as a Sharpie)
Chemicals provided: sucrose solution with a brilliant green or food coloring added.
Equipment needed:
4-ft length of 4 mm inside diameter (7.5 mm outside diameter) soft glass
tubing (glass box - 0162)
36” ringstand (0732)
copper wire (0732A - tool drawer)
pliers (0732A - tool drawer)
wire cutter (0732A - tool drawer)
Chemicals needed:
deionized distilled water
Each osmosis demonstration requires approximately 200 mL of a saturated sucrose solution. Make
500 mL as needed. The solubility of sucrose is 1 g of sucrose per 0.5 mL of cold water (1 g of
sucrose per 0.2 mL of boiling water). Tint the sucrose solution with brilliant green or methylene
blue to make the solution visible from a distance.
Lubricate one end of the glass tubing with water or glycerin. Slip the rubber stopper on the end of
the glass tubing. Then end of the glass tubing is even with the bottom of the stopper. Put the tubing
in the clamp on the ringstand. Fill the reaction cylinder with distilled water, and place it on the
ringstand’s base.
The dialysis tubing must be soaked in distilled water for over an hour before it can be used. Soak
two pieces one foot long. The extra piece is in case of damage to the first piece.
Double over one end of a piece of soaked dialysis tubing. Fasten it in a Spectra/Pro weighted
closure and wrap the end of the weighted closure with rubber bands to keep it closed.
Cut a pair of six inch pieces of #20-#22 gauge copper wire. One will be used to fasten the dialysis
tubing to the glass tube. The second is a spare in case the first piece breaks when twisted.
Just before the lecture, fill the dialysis tubing bag to the top through the funnel with the sucrose
solution. Pull the bag up over the rubber stopper on the end of the glass tubing. Take a piece of
copper wire and put two turns around the bag where it fits over the rubber stopper. With pliers, pull
the copper wire tight and twist the ends together to make a water tight closure. Curl the sharp ends
of the wire back to prevent them from snagging skin or clothes.
136
Osmotic Pressure (continued)
Clamp the glass tube in a vertical position with the bag totally immersed in the Berzelius beaker of
distilled water. Water immediately begins to osmose through the bag into the sugar solution. Once
assembled, the demonstration cannot be stopped. Within a few minutes, the solution rises above the
level of the rubber stopper.
Demonstration
Mark the level of the sucrose solution on the tube with a marker at the beginning of the lecture. If
the demonstration was properly prepared, the sucrose solution will overflow the top of the glass
tubing by the end of the lecture.
Reference
Shakhashiri, B. Z., “Chemical Demonstrations”, University of Wisconsin Press, Madison, WI,
Vol. 3, Experiment 9.20, pages 286-289.
137
TITLE:
TOPIC:
Radial Chromatography of Ink
Solutions
DEMONSTRATION
(Kit)
17.6
Preparation
Equipment provided: Assortment of pens with water-soluable inks. (Pens for overhead projectors
work well. Desirable colors include red, black, brown, green, yellow, purple,
etc.) One assortment per room.
3 oz. paper cups (or 100 mL plastic beakers). One per student.
Filter paper, Whatman #1, 11 cm circles with a 1/8 inch diameter hole in the
center. One per student.
Filter paper, Whatman #1, 11 cm circles cut into eight pie shaped segments.
One segment per student.
Chemicals needed:
Water. 75-90 mL per student.
Demonstration
The filter paper circle is lightly dotted with different inks in a circle about 1/4-inch out from the
center hole.
The beaker is filled with water. The point of the pie segment of filter paper goes through the nail
hole in the filter paper circle. The pie segment is lowered into the water, and the filter paper circle
rests on the beaker rim. Water wicks up the pie segment to the filter paper circle. As water spreads
out from the center of the circle, it carries the ink along. Different inks move at different speeds,
which causes inks made of a combination of pigments to separate into the component parts. Stop
when the wet area is almost ¼ inch from the edge of the filter paper circle.
Waste Disposal
All solutions can be washed down a sink. Waste paper goes into the trash.
138
TITLE:
TOPIC:
Liquid Nitrogen Ice Cream
Solutions and Solids
DEMONSTRATIO N
17.8
Preparation
Equipment needed:
Plastic bucket
Mixing stick or large wooden spoon
Plastic tea spoons
Disposable paper or plastic cups (~7 oz.)
Large serving spoon
Teri towels
Chemicals needed:
8 cups whole milk
8 cups heavy cream
2 2/3 cups superfine sugar
Vanilla to taste (1/2-2/3 cups)
Liquid nitrogen (~4 L)
Alternate: A-E Ice Cream Mix
($3.99 / 1/2 gal – 2006)
Liquid Nitrogen
This amount of material makes a double size batch, enough ice cream for approximately 40 people.
Demonstration
In a large plastic bowl, combine the milk, heavy cream, sugar, and vanilla. Stir with a wooden spoon
until the sugar is mostly dissolved. Scrape the sides of the bowl so the sugar does not collect there.
Add the liquid nitrogen while stirring the mixture vigorously to ensure the mixture is properly
aerated (nitrogenated). Continue stirring until the mixture is frozen, which could take up to ten
minutes, depending on the size of the batch. Serve and eat.
Safety and Waste Disposal
As the ice cream will be eaten, all materials should be kept isolated from the ordinary laboratory
chemicals and equipment.
Liquid nitrogen is very cold and can frostbite unprotected skin.
All materials except liquid nitrogen can be safely mixed with water and washed down a sink. Excess
liquid nitrogen can be discarded outside the building on the grass in one of the courtyards.
139
TITLE:
TOPIC:
Re-Gelation of Ice
Solutions and Solids
DEMONSTRATION
17.9
Preparation
Equipment provided: Plexiglas brackets with attached lattice feet, wooden brackets (prototype unit),
2 aluminum rods, 2-1 Kg weights connected with a 28 gauge steel wire, tray
(made from plastic bottle) for freezing ice block, cut-down plastic shoebox.
Equipment needed:
2 medium-sized ringstands, 2 clamps (to attach the aluminum rods to the
ringstands), gloves for handling the ice, 12 inches of ~28 gauge steel wire,
needle-nosed pliers, styrofoam box for the ice block.
Chemicals needed:
Ice block, approximately 10x5x1 inches.
Freeze the block of ice ahead of time. Make sure the steel wire connecting the weights is unbroken.
If necessary, use the needle nosed pliers to tie new wire to the weights. Attach the Plexiglas brackets
to the ringstands using the clamps and aluminum rods as shown in the picture below. Set the
cutdown plastic shoebox under the brackets to catch the meltwater and the falling weights.
Demonstration
Place the ice block on edge in the bracket
notches. Hang the two metal weights over the
ice. The pressure of the connecting wire
lowers the melting point of the ice, which
melts directly under the wire, and the wire
slowly moves downward. It takes about 30
minutes for the wire to migrate to the bottom
of the ice, letting the weights fall into the
plastic box. The water refreezes above the
wire, and the ice block remains in one piece.
Safety
Use needle-nosed pliers when tieing the wire to the weights. Handle the wire and the weights by the
weights. The wire is easily broken and thin enough to produce pressure cuts in unprotected skin.
Clean-up
Take the apparatus apart and dry it to keep it from corroding. Return the materials to the kit.
Reference:
Herbert W. Roesky. Spectacular Chemical Demonstrations. Wiley-Vch Verlag GmbH & Co. KGaA,
Weinheim, 1970. Experiment 5: Re-Gelation of Ice.
140
TITLE:
TOPIC:
Crystal Samples
Solutions and Solids
DEMONSTRATION
17.11
Preparation
Chemicals needed:
quartz crystal (Gilman 0162, Mineral Samples, box 5) and/or chromium (III)
potassium sulfate crystal (Gilman 0162, with the supersaturated sodium
acetate)
Demonstration
Display one or both crystals.
chromium (III) potassium sulfate
quartz
Note: The chromium (III) potassium sulfate crystal must remain wet. If it dries out, it will go to
powder. That is why the crystal is kept in a sealed desiccator with solution in the bottom.
Safety
Chromium (III) potassium sulfate can irritate the skin, eyes, gut, and respiratory tract. It is also an
allergen. Either keep the crystal in the desiccator (preferred) or wear protective eyewear and gloves.
In this form, quartz is not considered a health hazard.
141
TITLE:
TOPIC:
Chemical Color Change With Temperature
Solutions and Solids
DEMONSTRATION
(Kit)
17.12
Preparation
Chemicals provided: Two sets of three large test tubes containing sulfur, mercury (II) iodide, and
potassium dichromate.
Chemicals needed:
1 L of liquid nitrogen in a 2 L dewar flask.
Equipment needed:
black and white wooden test tube racks
Demonstration
Put one set of chemicals on a rack as the standard. Immerse the other set of chemicals in liquid
nitrogen until they change color. Put the test tubes on a rack so the colors can be compared with the
standard set.
On cooling, sulfur changes from yellow to white, mercury (II) iodide changes from red to yellow,
and potassium dichromate changes from orange to yellow. The color changes are due to a changed
crystal structure.
Safety
Both mercury (II) iodide and potassium dichromate are toxic chemicals. The tubes are stoppered and
sealed to prevent human exposure, but low temperatures produce a partial vacuum in the sealed
tubes. Handle them gently to avoid breaking them.
Reference
Day, Jesse H. 1968. Thermochromism of inorganic compounds. Chemical Reviews 68(6): 649-657.
142
TITLE:
TOPIC:
The Mole
Stoichiometry
DEMONSTRATION
(Kit)
18.1
Preparation
Equipment needed:
White wooden test tube rack (Gilman 0162)
Chemicals provided: H2O, Al, S, Fe, NaCl, Cu, I, CuSO4•5H2O, Al2(SO4)3•18H2O, C12H22O11
(sucrose)
One mole of each of the chemicals is weighed and placed in an appropriate container for display.
Substance
H2O
Al
S
Fe
NaCl
Cu (as pennies)
I
CuSO4•5H2O
C12H22O11 (sucrose)
Al2(SO4)3•18H2O
Weight (g)
18.0 g
26.98
32.06
55.85
58.45
63.54 g
126.90
249.71
342.30
666.41
Display Container
Test tube (small)
Test tube (small)
Test tube (small)
Test tube (small)
Test tube (large)
Test tube (small)
Test tube (large)
Bottle (clear)
Bottle (clear)
Bottle (clear)
Demonstration
Call the students attention to the fact that although the weights and volumes vary considerably, each
container has exactly one mole of the substance in it.
Waste Disposal
Check the containers to be sure they are well sealed. If necessary, use fresh Parafilm or vinyl
electrical tape. Store the mole sample until needed again.
143
TITLE:
TOPIC:
Coin Operated Chemistry—Red, White and Blue
DEMONSTRATION
____
When two copper coins are added to a three flask system containing unequal amounts of colorless
solutions, a number of visual changes occur. After twenty minutes the solutions in the flasks are
equally distributed and appear red, white, and blue.
Equipment needed:
400 mL .40 M sodium hydroxide, NaOH (To prepare 1 liter of .40 stock
solution, dissolve 16 g NaOH in distilled water and dilute to 1 liter.)
1140 mL .10 M nitric acid, HNO3
1 mL phenolphthalein
25 mL concentrated nitric acid, HNO3
2 copper pennies (USA pennies minted before 1983)
3 1-liter long neck Florence flasks or 1 liter round bottom flasks
1 2-hole stopper to fit flask
1 1-hole stopper to fit flask
4 right angle glass tubing (1 cm OD) bends (10 cm × 18 cm)
15 cm rubber tubing to fit glass tubing
3 ringstands and clamps
Procedure
Assemble the three flask system as shown in the following sketch
Each flask should be securely attached to a ringstand by means of a clamp.
Wearing gloves, add 400 mL of .40 M sodium hydroxide to flask number one; add 1140 mL of
.10 M nitric acid and 1 mL of phenolphthalein to flask number two; and 25 mL of concentrated nitric
acid to flask number three. Securely stopper the middle flask.
To perform the demonstration, add two copper pennies to flask number three and securely stopper.
144
Coin Operated Chemistry (continued)
Hazards
Nitric acid is a strong acid and a powerful oxidizing agent. Contact with combustible materials can
cause violent and explosive reactions. The liquid can cause severe burns to the skin and eyes. The
vapor is irritating to the eyes and to the respiratory system.
Disposal
Solutions in the first and second flasks can be neutralized and flushed down the drain. Since the
solution in the third flask is highly acidic, it should be neutralized with sodium bicarbonate or soda
ash and flushed down the drain.
Discussion
The two copper pennies react with the concentrated nitric acid to produce a large volume of nitrogen
dioxide gas in flask number three. The pressure from this gas production forces air from flask
number three into the second flask which forces half of the dilute nitric acid and phenolphthalein
solution from this middle flask into the first flask. As the phenolphthalein mixes with the more
concentrated sodium hydroxide, flask number one turns red.
The extremely soluble, brown, nitrogen dioxide gas eventually enters the middle flask and dissolves,
causing the middle solution to become even more acidic. As the reaction of copper with
concentrated nitric acid nears completion, the third flask begins to cool. This cooling along with the
nitrogen dioxide dissolving, reduces the gaseous pressure so that the atmosphere is able to push half
of the red basic solution in the first flask into the more acidic middle flask. The excess acid in the
middle flask causes the solution to remain colorless. At the same time, this colorless solution turns
blue upon entering the third flask due to the presence of the copper(II) ions from the reacting
pennies. After about twenty minutes the solution volumes in the three flasks are approximately
equal and respectively colored “red”, “white”, and “blue”.
This demonstration was developed by Ron Perkins with the assistance of Karen Spencer while on
the staff of the Institute for Chemical Education, University of Wisconsin - Madison, the summer of
1985.
145
TITLE:
TOPIC:
The Ethanol Cannon
Thermochemistry
DEMONSTRATION
(Kit)
19.12A
Procedure A. The Small Cannon
Preparation
Equipment provided: 1 L plastic bottle with 2 nails in it, cork stopper (with or without sponge
rubber ball), ringstand, three-finger clamp
Equipment needed:
Tesla coil
Chemicals needed:
2-3 mL of 95% ethanol (flammables cabinet, Gilman 0635)
Squirt a few milliliters of ethanol into the plastic bottle. Turn the bottle on its side and give it a good
rolling to distribute the ethanol on the sides. Holding the bottle up to the light while rolling it makes
it easy to see the coating action. The film of ethanol vaporizes to produce an ethanol vapor/air
mixture in the bottle. Stopper the bottle, and put it in the ringstand at about a 45o angle.
Demonstration
Touch the Tesla coil to a nail to produce a spark between the tips of the two nails. Ethanol vapor
explodes and blows the cork 10 m or more.
Safety
Ethanol is flammable. Hold the Tesla coil by the grip end. It can give a good tingle if held too close
to the tip when running.
Clean Up
Put the open bottle in a hood to allow vapor to dissipate.
Note: O2 in the bottle is used up in the firing. Blow into the bottle to replenish the O2
for a repeat firing, if one is necessary.
146
TITLE:
TOPIC:
The Ethanol Cannon
Thermochemistry
DEMONSTRATION
19.12B
Procedure B. The Super (20 L) Ethanol Cannon
Preparation
Equipment needed:
20 L plastic bottle (of the sort used for bottled water), rubber stopper to fit the
bottle’s neck, crucible tongs, applicator sticks, matches
Chemicals needed:
95% ethanol
Squirt around 5 mL of ethanol into the plastic bottle. Hold the bottle on its side and give it a good
rolling to distribute the ethanol on the sides. Holding the bottle up to the light while rolling it makes
it easy to see the coating action. The film of ethanol vaporizes to produce an ethanol vapor/air
mixture in the bottle. Stopper the bottle until use.
Demonstration
This demonstration is best done in a darkened room so that everyone can see the flame easily.
If there is open floor space over 25 feet long, put the bottle on its side on the floor, and remove the
stopper. Light a match, and ignite the end of an applicator stick. Bring the flaming applicator stick
to the bottle opening from above and slightly to the rear. The ethanol vapor/air mixture ignites
explosively. Flames fill the bottle and jet out of the neck, and the bottle is rocket-propelled across
the floor.
If there is insufficient space for the rocket, place the bottle upright on a bench, and remove the
stopper. Hold a lighted match in the crucible tongs, and drop it through the neck of the bottle. The
ethanol vapor/air mixture ignites explosively. A pale blue flame fills the bottle and jets out of the
bottle’s neck. When the oxygen in the bottle is exhausted, the flame goes out. Fresh air is sucked
into the bottle and mixes with the hot gases, giving residual ethanol vapor the opportunity to ignite
again in pulses.
Safety
Flames flash out of the bottle’s neck on ignition. Keep your hands and body away from directly in
line with the neck. Keep everyone and anything that can burn at least six feet away from the bottle.
Do NOT do the rocket variation on carpet. Aim the rocket so that it will not hit the audience.
Replace the plastic bottle every year or two.
Waste Disposal
The burning of ethanol produces carbon dioxide and water. There may also be some unburned
ethanol left in the bottle. Drain any liquid into a sink, and put the open bottle (neck down) into a
hood to air out.
147
TITLE:
TOPIC:
The Metric System: Volume, Length, and Weight
Physical Properties
DEMONSTRATION
(Kit)
20.1
Preparation
Equipment provided: 1 L volumetric flask
1 L beaker
1 L soda pop bottle
1 kg iron rod
1 set of assorted weights (1 g, 10 g, 100 g)
Equipment needed:
1 L graduated cylinder
Meter stick
(Additional items, including an electronic balance, may be specially
requested.)
Demonstration
Various pieces of equipment illustrate the metric system. Several items in the kit are duplicated in
case two classes want the demonstration at the same time.
148
TITLE:
TOPIC:
Density
Physical Properties
DEMONSTRATION
(Kit)
20.2A
Procedure A. Classic Coke Vs. Diet Coke
Description
A can of regular Coca-Cola sinks in water while Diet Coca-Cola floats. Increasing the water density
with NaCl makes the can of regular coke float. Decreasing the water density with 95% ethanol
makes the can of diet coke sink.
Preparation
Equipment needed:
2 - 4 L beaker
1 - 12 fluid ounce can of regular Coca-Cola
1 - 12 fluid ounce can of Diet Coca-Cola
stirring rod
Chemicals needed:
900 mL 95% ethanol
60 g sodium chloride (table salt)
tap water
Put 2-2.5 L of tap water in each beaker.
Demonstration
Note: When putting a coke can in the water, put it in on its side. This will allow air trapped in the
recessed bottom to escape.
Put the regular Coca-Cola can in a beaker. It sinks. Put the Diet Coca-Cola in the same beaker. It
floats.
Remove the diet coke can from the beaker. Add 60 g of NaCl to the beaker holding the regular coke,
and stir well. The regular coke floats as soon as enough NaCl dissolves.
Put the Diet Coca-Cola can in the second beaker. The can floats. Add 900 mL of 95% ethanol. The
reduced density of the solution lets the can sink to the bottom.
Waste Disposal
All solutions can be safely flushed down the sink.
149
TITLE:
TOPIC:
Density
Physical Properties
DEMONSTRATION
(Kit)
20.2B
Procedure B. Golf and Bowling Balls
Preparation
Equipment provided: 3 bowling balls, golf ball, aluminum rod with clamp, vernier calipers, 12”
ruler
Equipment needed:
ringstand (medium sized), clear plastic container such as a battery jar
Optional equipment (must be specifically requested): cork ring, electronic balance (6 kg capacity)
Demonstration
Ask the students to predict which of the balls will float and which will sink in water.
The bowling ball and the golf ball are weighed individually, using the cork ring to keep each one
from rolling off the balance. The golf ball’s diameter is measured with the vernier calipers. The
diameter of each bowling ball is measured by putting each ball between the ringstand base and the
aluminum rod and then using the ruler to measure the gap.
The volume of each ball is calculated using the formula Vsphere = 4/3 πr3. The density is calculated
with the formula density = mass/volume.
If an object has a density greater than 1, it sinks in water. If an object has a density less than 1, it
floats in water. Each ball is placed in a clear container of water to prove whether it sinks or floats.
Golf Ball
Bowling Ball 1
Bowling Ball 2 Bowling Ball 3
(black & red)
(green)
(black)
Diameter
4.25 cm
21.6 cm
21.6 cm
21.6 cm
Radius
2.125 cm
10.8 cm
10.8 cm
10.8 cm
Volume*
40.2 cc
5276.7 cc
5276.7 cc
5276.7 cc
Mass
45.6 g
6085.8 g
4954.1 g
3568.3 g
Density
1.13 (sink)
1.15 (sink)
0.94 (float)
0.68 (float)
*The volumes given are for spheres. The volumes were not adjusted for the finger holes in the
bowling balls or dimples on the golf ball.
Reference
Mason, Diana; Griffith, William F.; Hogue, Sharon E.; Holley, Kathleen; and Hunter, Kirk. 2004.
Discrepant event: the great bowling ball float-off. J. Chem. Educ. 81 (9): 1309-1312.
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TITLE:
TOPIC:
Atmospheric Pressure
Physical Properties
DEMONSTRATION
20.3
Description
An iron bar one square inch in cross section and weighing 14.7 pounds is rested on a person's foot.
Preparation
Equipment needed:
iron bar one square inch in cross section and weighing 14.7 pounds
Demonstration
The end of the iron bar is gently placed on a student’s foot. The bar’s end has an area of one square
inch. The bar weighs 14.7 pounds. The bar’s pressure on the foot is equal to atmospheric pressure.
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