http://www.woodrow.org/teachers/ci/faraday/lab4.html
The 1827 Christmas Lectures
of Michael Faraday
Demonstration of Lecture #4 Today
Nitric Acid or Aquafortis -- Ammonia or Volatile Alkali -- Muriatic Acid or Spirit of Salt
-- Chlorine
Teacher Presentation
Today's interpretation is in two parts:
1. Demonstration notes (e.g. lesson plans) of how Faraday might have planned for his
lectures if he were to step into today's classroom;
2. A more detailed description of the modern day interpretation for performing some
of his actual experiments, or experiments which illustrate the same principles he
showed. Included in this are the demonstrations performed by the group in the reenactment of this lecture at the close of the WWNFF Institute, July 1992.
It should be noted that some of Faraday's methods and materials used are currently
considered hazardous for safety or health reasons. Selected modern day demonstrations that
are hazardous or difficult to perform are available on videodisc or tape.
For the corresponding original experiments, click on the icons
Nitric Acid
Lab. 2: Acidic Properties Using Indicators
To demonstrate the acidic properties of nitric
PURPOSE
acid using indicators.
MATERIALS
Test-tube rack, 3 test tubes, nitric acid
solution, litmus paper, cabbage juice, turmeric
.
solution, droppers for indicators.
HAZARDS
Nitric acid is very corrosive. It may cause
burns to skin or damage clothing. Flush any
exposed area with water immediately.
PROCEDURE Pour a milliliter of dil. nitric acid into test
tube. Test with litmus and watch for color
change. Repeat with cabbage juice. Repeat
with turmeric.
DISPOSAL
The acid may be poured down the drain and
flushed with plenty of water.
DISCUSSION Distilled water with a known acid or base may
be used to compare color changes. Litmus
turns red in an acid and blue in a base. Red
cabbage juice is red in acid and green in base.
Turmeric is pale yellow in acid, orange when
neutral, and red-brown in a strong base.
Lab. 4: Nitric Acid Stains - (a Xanthoproteic Reaction)
To show the effect of nitric acid and ammonia
PURPOSE
on natural materials.
MATERIALS
25 mL 3M HNO3, 25 mL 3M NH3 small
pieces of wool (washed), silk, cotton, etc.
HAZARDS
Nitric acid and ammonia should be handled
with care; wear goggles and apron.
PROCEDURE Dip each piece of fabric into warm dilute acid.
The wool and silk will change to a yellow
color; cotton shows no change. Then dip each
fabric in the ammonia. The natural fibers of
wool and silk change to a bright orange; cotton
remains unchanged. You may continue to dip
fabrics back and forth between solutions,
noting the color changes.
DISPOSAL
Neutralize both solutions and flush down
drain.
DISCUSSION Nitric acid also produces a yellow stain on
skin. In the ``Xanthoproteic Reaction'' from
Practical Physiological Chemistry, by Hawk,
Oser and Summerson (McGraw-Hill: New
York, 1954) the authors reacted 2-3 mL egg
albumin with 1 mL conc. HNO3, which was
warmed and changed to yellow. It was allowed
to cool and NH4OH was added to excess and
the orange color appeared. The authors
suggested that the reaction could also be done
with 0.1% phenol solution instead of the
protein. Explanation: ``Due to the presence of
the phenyl group -C6H5 in protein molecules
with which HNO3 forms certain nitromodifications. The particular complexes of the
protein molecules which are of special
importance (e.g. egg albumin), are those of
tyrosine and tryptophan.''
Lab. 5: Copper and Nitric Acid
To show the different reactions between
PURPOSE
concentrated and dilute nitric acid and copper.
MATERIALS
Conc. HNO3, deionized water, 2 -50 mL grad.
cylinders, 2 -150 mL beakers, 2 copper
pennies (pre-1982) or pieces of copper.
HAZARDS
Handle nitric acid with caution (goggles and
apron). Perform this demonstration in fume
hood.
PROCEDURE Add 25 mL of conc. acid to one beaker. To the
second beaker, add 12.5 mL conc. acid + 12.5
mL water. Place a penny in each beaker. Note
color differences/similarities of solutions and
gases formed in each.
DISPOSAL
Allow each reaction to come to completion,
then neutralize and flush down drain with
plenty of water. Copper pieces may be
discarded.
DISCUSSION Reactions (redox) are as follows: (Conc. acid)
Cu + 4 H+ + 2NO3- --> Cu2+ + 2 NO3- + 2 H2O
(Dil. acid) 3 Cu + 8 H+ + 2 NO3- --> 3 Cu2+ +
2 NO + 4 H2O Different concentrations of
nitric acid produce different gases: darkbrown NO2 mixed with colorless NO. Both
produce the blue Cu2+ ion. Alternative: ``The
Periodic Table'' (videodisc) Journal of
Chemical Education Software: Sequence
#29501-30261 shows the reaction with two
concentrations of nitric and hydrochloric
acids.
Ammonia
Lab. 13: Alkaline Properties of Ammonia
To illustrate the alkaline properties of
PURPOSE
ammonia.
MATERIALS
Hotplate, test tube rack, 3 test tubes with
rubber stoppers, NH3(aq), litmus solution, red
cabbage juice, turmeric solution.
HAZARDS
Ammonia is irritating to the respiratory system
and eyes, and can cause severe burns.
Mixtures of ammonia gas and air can be
explosive and should be kept away from
sparks.
PROCEDURE Gently heat a test tube containing an aqueous
ammonia solution in a water bath on the
hotplate. Waft the gas to detect the odor. Add
litmus to the test tube and note color change.
Repeat with a different test tube and cabbage
liquor as the indicator. Repeat using turmeric
as the indicator.
DISPOSAL
Fill ammonia, generating tube with water.
Flush all solutions down drain.
DISCUSSION The normal boiling point of ammonia is 33.35°C. It is a colorless gas with pungent
odor and is extremely soluble in water. A
saturated solution at 25°C is 34% by weight of
ammonia. The solution is basic.
Lab. 14: Solubility of Ammonia in Water
To demonstrate the solubility of ammonia in
PURPOSE
water.
MATERIALS
250 mL round flask fitted with two hole
stopper and long piece of glass tubing (see
teaching diagram), 500 mL beaker, ring stand
with clamp, phenolphthalein, eye dropper,
concentrated NH4OH or bottle of compressed
NH3 gas.
HAZARDS
Use same care in handling ammonia as in
previous experiment.
PROCEDURE Set up apparatus: insert glass tubing in rubber
stopper. Fill eye-dropper with water and insert
in other hole in stopper, insert in round flask.
Fill beaker with water and add a few drops of
phenolphthalein. Invert round flask and clamp
as shown (teaching diagram). Flask must be
dry. Add NH3 from compressed gas bottle (or
generate and collect some as suggested in
previous experiment). Squeeze a little water
into the flask from the eye dropper. The
fountain effect is observed as the NH3
dissolves in the water. Note change in
indicator color. (Ammonia can also be
generated by method in Lab. 22.)
DISPOSAL
Carefully dilute all solutions and flush down
drain.
DISCUSSION The extreme solubility of NH3 causes it to
dissolve immediately in the small amount of
water squirted into the flask. With a resulting
decrease in pressure in the flask, the water will
rise quickly giving the ``fountain'' effect. The
color change in the indicator indicates the
presence of the base. NH3(g) + H2O (l) -->
NH4+ (aq) + OH- (aq) Also demonstrated on
videodisc: ``Chemistry at Work'', Sequence:
B-03752.
Lab. 17: Ammonia and Acid Neutralization
To illustrate the ability of ammonia to
PURPOSE
neutralize an acid.
MATERIALS
Test tube rack, 6 test tubes with rubber
stoppers, dil. NH4OH, dil. HNO3 in dropper
bottle, litmus solution, red cabbage juice,
turmeric solution, distilled water.
HAZARDS
See previous lab (Lab. 13)
PROCEDURE Place a small quantity of each indicator in
each of three test tubes. Add ammonia
solution. Then add acid, drop by drop, until a
color change is noted. Compare with water
and indicator to find the neutral point.
DISPOSAL
Dilute solutions and flush down sink.
DISCUSSION Ammonia is a base and can be neutralized by
acid solutions. Litmus is blue in base, red in
acid. Red cabbage juice will be green to
greenish- yellow in base, blue when neutral,
and red in acid. Turmeric will be reddishbrown in base, yellow-orange when neutral,
and yellow in acid.
Lab. 22: Combustion of Ammonia
To show that ammonia gas will burn in the
PURPOSE
presence of oxygen.
MATERIALS
Y-tube apparatus for mixing gases (as shown
in illustrated notes for this lecture), ammonia
generator (10 g NH4Cl and 10 g Ca(OH)2; add
10 mL distilled water and heat gently), oxygen
generator (3% H2O2 and 3.0 g KMnO4
dissolved in 60 mL 3M H2SO4), candle.
HAZARDS
Generate small quantities of NH3 and O2. Be
prepared to pinch shut the O2 line in case
flame backs into apparatus. Dismantle oxygen
generator immediately after use. Ammonia:
same hazards as in above experiments.
PROCEDURE Set up gas generators and connect to Y-tube.
Add pea-sized sample of MnO2 ONLY to
generator. Use pinch clamp to shut line to O2
generator. Begin generation of NH3. Fill
inverted beaker with NH3. (A piece of red
litmus placed at mouth will indicate that
beaker is full.) Remove fill tube. Bring candle
flame to mouth of beaker and watch for bright
flash as NH3 ignites. Pour a small amount of
H2O2 into oxygen generator and repeat using a
mix of NH3 and O2. (Alternative: light mix of
the two gases as they emerge from the Ytube.)
DISPOSAL
Fill generator flasks with water and flush
down sink.
DISCUSSION This demonstration shows that NH3 is
flammable in both air and pure oxygen. The
reaction with oxygen is more dramatic. Both
reactions are strongly exothermic: 4 NH3 + 3
O2 --> 2 N2 + 6 H2O
Hydrochloric Acid
Lab. 24, 26, 31: Preparation and Properties of Hydrochloric Acid
To show the preparation of HCl and
PURPOSE
demonstrate its solubility and its effect on
various indicators.
MATERIALS
250 mL flask with ground glass opening, 500
mL flask with ground glass opening, ground
glass joint, conc. H2SO4, NaCl solid,
indicators (litmus, turmeric, universal), ground
glass stopper, large beaker or transparent
container, dilute NaOH.
HAZARDS
HCl should be prepared under a hood and care
taken as vapors are corrosive and should not
be inhaled.
PROCEDURE Join 250 mL flask (gas generator) to 500 mL
flask using a vented ground glass connection
for collection of HCl by upward displacement
of air. Under the hood disconnect 250 mL
flask from apparatus and add 10 g of solid
NaCl to the flask and about 20 mL conc.
H2SO4. Immediately reconnect apparatus.
Allow 500 mL flask to fill with ``fog'' of HCl;
(excess HCl will be vented through side-arm
of flask or of ground glass joint). Disconnect
500 mL flask from apparatus, stopper, and
slowly add dil. NaOH to 250 mL flask to stop
reaction. Demonstrate solubility of HCl in
water with same procedure as with NH3 (Lab.
14). Test the solution of HCl formed above
with litmus, cabbage juice and turmeric.
Universal indicator could have been added to
the water in the solubility demonstration to
show formation of the acid.
DISPOSAL
Carefully dilute all solutions and flush down
drain.
DISCUSSION Formation of HCl (at moderate temperatures):
NaCl + H2SO4(r) NaHSO4 + HCl (at higher
temperatures): NaCl + NaHSO4 --> Na2SO4 +
HCl (combining both steps): 2 NaCl + H2SO4 -> Na2SO4 + 2 HCl
Lab. 34: Reaction of Hydrochloric Acid and Ammonia (also illustrates Graham's Law
of Diffusion)
To illustrate the reaction of NH3 and HCl and
PURPOSE
[qualitatively/semi-quantitively] show the
progressive rate of diffusion of these gases,
using pH paper.
MATERIALS
Glass tube (length may vary up to 75 cm,
inside diameter up to 3 cm - smaller tubes
work faster), ring stand with clamp to hold
glass tube, conc. HCl, conc. NH3, 2 corks to fit
ends of tube, Q-tips or cotton balls attached to
corks, pHydrion paper a little longer than
length of tube.
HAZARDS
Conc. acids and bases should be handled with
care (goggles and gloves). Product formed
(NH4Cl) is irritating - use in well-ventilated
room.
PROCEDURE Pull a piece of full-range pH paper through the
entire length of the glass tube, tape ends to
outside of tube (attach heavy paper clip to one
end of paper and let it fall through). Attach
tube to clamp so that it is horizontal. Attach Qtips or cotton balls to corks, soaking one in
HCl, the other in NH3. Place corks
simultaneously in opposite ends of tube. Note
rate of diffusion by color change in pH paper.
Note distance of the NH4Cl white ring from
each end.
DISPOSAL
Rinse cotton balls and discard. Rinse glass
tube thoroughly.
DISCUSSION Reaction: NH3 (g) + HCl (g) --> NH4Cl (s)
The rate of diffusion of gases is inversely
related to the square root of their molecular
masses. Since HCl (MM = 36.5) has greater
mass than NH3 (MM = 17), the NH3 diffuses
more rapidly. The pH paper allows one to see
the progress of each gas. An extension of this
is to quantitively determine how closely these
gases behave with respect to Graham's Law
(distance travelled is proportional to diffusion
rate if both gases are introduced into the tube
at the same time and at the same partial
pressures. Don't expect accurate results as
maintaining concentrations is difficult.)
Chlorine
Lab. 41: Bleaching Properties of Chlorine
To demonstrate the bleaching properties of
PURPOSE
chlorine.
MATERIALS
10 mL 5% NaClO (Clorox), 100 mL 1M HCl,
250 mL Erlenmeyer flask, glass plate, flower
petals of blue or red pigment, red food color,
vinegar, Petri dish.
HAZARDS
Cl2 is a noxious gas, use well-ventilated hood.
The gas irritates eyes; if inhaled, can cause
lung irritation; in high concentration is
irritating to the skin. Cl2 is a strong oxidizing
agent: combustible materials may burn in it;
acetylene may form an explosive mixture.
PROCEDURE Pour 100 mL of 1.0 M HCl into the flask. Add
10 mL of 5% NaClO. Cover with the glass
plate. Within a minute the flask should fill
with yellow-green Cl2 gas. Suspend the flower
petals in the flask and observe results. Pour
enough water in Petri dish to cover bottom.
Add 10 drops of red food color and stir. Add 3
mL of clorox to the solution and observe for
about 20 sec. Add a few drops of vinegar and
observe.
DISPOSAL
Dilute the solution before flushing down the
drain. Wash containers with soap and water.
DISCUSSION Chlorine is a yellow-green gas with a
suffocating odor. It has the ability to bleach
certain fabrics such as indigo dye in blue jeans
and the pigments in some flowers (blue
delphiniums give a nice result). The chlorine
oxidizes the red food color over a long period
of time. The result is more dramatic with the
addition of vinegar. See Shakhashiri, Vol. 2,
pp. 220-227 for others.
Lab. 44: Combustion of Chlorine and Hydrogen
Due to the explosive nature of this reaction it is unsuitable for classroom
demonstration. It is shown on the videodisc: ``Chemistry at Work'' Sequence A00444. (Videodiscovery, Inc.; Seattle, WA. phone: 1-800-548-3472)
Go to the original experiments
.
Reference
Shakhashiri, Bassam Z., Chemical Demonstrations, vols 2-3, University of Wisconsin Press,
Madison, 1985 (V.2), 1989 (V.3).
Authors
Michael P. Kelly, R. James Kurtz, Nancy LeMaster, Sara McCoy, Judith Moody, Daniel
Morton, Gerald Munley, and John Oliver.