Lab Activities
Chemistry 30 - Calorimetry
Content Introduced/Reinforced
 Introduced:
Endothermic and exothermic reactions
Total heat of solution & calculations
Q = mcT
Molar heat of solutions & calculations
Molar heat solution = (total heat solution)/(moles solute used)
 Reinforced:
Ions
Balancing equations
Percent error
Curriculum Connections
 Examine the relationships between heat and energy and reactions
Recognize that energy changes are associated with chemical reactions
Differentiate between endothermic and exothermic reactions
Compare the energy changes in phases changes and chemical reactions
 Understand the quantitative description of enthalpy change
Measure some energy changes in chemical reactions
Investigate how tables of standard heats (enthalpies) of formation are created
and used
Express the enthalpy change of a chemical reaction as a term in the equation for
the reaction, or as a heat of reaction ΔH)
Concept Connections
 Past Concepts:
Thermochemistry
Calorimetry
Energy
Law of Conservation of Heat
Temperature vs. Heat
Specific Heat
 Future Concepts
Hess’s Law
Materials
 2 styrofoam cups
 Thermometer
 ~15g of anhydrous sodium acetate (CH3CO2Na)
 ~15g of ammonium nitrate (NH4NO3)
 Water
 100mL graduated cylinder
 balance
Procedure
 1. Accurately find the mass of about 150 mL of tap water. Record this value
and other measurements in the data table. Add the water to the Styrofoam
cup calorimeter.
 2. Accurately find the mass of about 15 g of solid ammonium nitrate.
 3. Find and record the initial temperature of the water. Record to the nearest
0.2C.
 4. Dissolve the solid ammonium nitrate in the water, stirring with the
thermometer. Record the maximum temperature difference from the initial
reading.
 5. Repeat the experiment using a sample of about 15 g of sodium acetate in
place of the ammonium nitrate.
Student Lab Activity
 Measure experimentally the amount of heat involved in the dissolving of
~15g ammonium nitrate (NH4NO3) and ~15g sodium acetate (CH3CO2Na) in
~150mL of water.
 Record your data in a representative format.
 Using the equation discussed in class, calculate the total and molar heat of
solution for each of the two solids. (specific heat of water = 4.18J/g°C)
Questions
 Both of the substances used in this experiment consist of ions. Give the
chemical formulas for the two ions that make up each of the compounds used
in this experiment.
Ammonium nitrate:
Sodium acetate:
 For each of the dissolving processes, state whether the overall process was
endothermic or exothermic.
 Write balanced equations for the dissociation of each ionic compound. Be
sure to include the value for the energy term that you obtained during your
experiment.
 If there was discrepancy between your observed value and the expected
value resulting in a percent error, why did this occur?
 What conclusions can you draw from your experimental data.
 Why use a Styrofoam cup?
Sample Data Table
Ammonium Nitrate
Sodium Acetate
Mass of cup + water (g)
100.6
103.4
Mass of empty cup (g)
1.6
1.6
Mass of water (g)
99.0
101.8
Mass of solid +
container(g)
39.9
38.4
Mass of empty container
(g)
23.3
23.2
Mass of solid used (g)
16.6
15.2
Initial water temperature
20.2
19.8
Final water
temperature
8.0
27.6
-12.2
+7.8
Change in water temp.
Things to Look Out For:
 Ammonium nitrate: exothermic
 Sodium acetate: endothermic
Safety Concerns
 Ammonium nitrate and sodium acetate are skin and eye irritants therefore
protective clothing, eye goggles, and rubber gloves and MUST be worn.
The Nature of a Chemical Reaction
Introduction
Changes go on about you all the time. Some changes are chemical changes, such as
gasoline burning or a nail rusting. But what is happening when a chemical change
occurs? What is the nature of a chemical reaction?
Purpose
To examine the behavior of matter in a chemical reaction, focusing on the behavior
of the individual particles of each substance involved.
Safety Considerations
Wear protective glasses and an apron at all times. Avoid skin contact with solids and
solutions. Dispose of all solutions in the container designated by your teacher. Wash
your hands before leaving the laboratory.
Procedure
Part I. Your teacher will demonstrate three reactions. Record your observations.
Then, answer these questions in your assigned discussion group:
1. What evidence for a chemical reaction did you observe in each demonstration?
2. Define "precipitate".
Part II. Assemble the following materials at your workstation: petri dish, vials
containing crystals of lead(II) nitrate, Pb(NO3)2(s), and potassium iodide, KI(s), spot
plate, small test tube, and two labeled, thin-stem pipets containing solutions of
lead(II) nitrate, Pb(NO3)2(aq), and potassium iodide, KI(aq). Record all your
observations in and complete sketches when appropriate.
1. Grinding of solids. Place a few crystals of solid lead(II) nitrate and solid potassium
iodide in the same well of a spot plate. Using the small test tube, carefully
grind the solids using a circular motion. Do not press too hard or you may
break the test tube.
2. Prepare petri dish. Cover the bottom of the petri dish with distilled water. Place
on a white sheet of paper.
3. Simultaneous addition of solutions. Using the thin-stem pipets, simultaneously
add 10 drops of lead(II) nitrate solution and 10 drops of potassium iodide
solution on opposite sides of the petri dish as shown in the diagram below.
Do not move or shake the dish.
4. Delayed addition of potassium iodide. Repeat Steps 2 and 3 but wait five minutes
before adding the potassium iodide solution.
5. Dump all solutions into the waste container provided. Using a small amount of
water, wash the solid from Step 1 into the waste container.
6. Wash hands thoroughly before leaving the laboratory.
Data Analysis, Concept
1. How do you know a chemical reaction occurred?
2. How were the results in Step 1 and Step 3 similar? How were they different?
3. Do you think the chemical reactions were the same in both Step 3 and 4? Why?
4. How is the observation in Step 3 different from that in Step 4? What do you think
caused this difference?
5. Why did it take longer in Step 3 for an observable change?
Imply, Apply
1. When the chemical substances used in this activity are placed in water, they
dissolve and individual particles making up the substance break apart. Since
the solution looks just like water, what can you say about the size of the
particles that make up each substance?
2. Draw a picture to show what you think these particles look like in water. Use XY
to represent a dissolved substance and W to represent water.
3. You started with two different substances at the beginning of Step 1. How do you
know a new substance was produced as the result of the grinding? Chemists
give this kind of chemical reaction the name "double replacement". It is kind
of a "changing partners" behavior. These substances "trade partners" to
become lead(II) iodide and potassium nitrate. The lead(II) iodide has a
yellow color, which you observed in the reactions. Since lead(II) iodide is not
very soluble in water, a precipitate (solid) forms in Steps 3 and 4.
4. Let AB represent one solid and CD represent another solid; let AD represent the
colored solid formed. Create a diagram that shows a model of the
microscopic behavior of these particles if equal quantities are ground
together as in Step 1.
5. Using the same symbols, write an equation for the reaction between AB and CD.
6. What would happen if more AB than CD is combined? Create a diagram to show
this.
Preparing for the Laboratory Activity
Major Chemical Concept
A model of the particulate nature of matter and a kinetic model of matter can be
developed in terms of the behavior of particles in chemical reactions.
Level
General chemistry
Expected Student Background
Students should be able to:
• Make and record observations in a notebook or data sheet.
Time
60 min (including questions and post-lab)
Safety
• The laboratory procedures involve no unusual hazards.
• The lead iodide must not be dumped in sink.
• Be sure excess KI is added to the solutions to ensure all the PbI2 precipitates.
Materials
Non-Consumables (per lab team)
• 1 Microspatula
• 1 Petri dish bottom or lid, glass or plastic
• 1 Spot depression plate or watch glass and 13 x 100 mm test tube
Consumables (per lab team)
•
•
•
•
Thin-stem pipet containing 0.25 M lead(II) nitrate, Pb(NO3)2
Thin-stem pipet containing 0.50 M potassium iodide, KI
Vial, small, containing crystals of lead(II) nitrate, Pb(NO3)2
Vial, small, containing crystals of potassium iodide, KI
Advance Preparation
1. Pre-lab Teacher Demonstration
◦
0.1 M sodium carbonate, Na2CO3, 4 g per 500 mL
◦
0.1 M calcium nitrate, Ca(NO3)2, 4 g per 250 mL
◦
0.02 M iron(III) chloride, FeCl3, 0.8 g per 250 mL
◦
0.001 M potassium thiocyanate, KSCN, 0.03 g per 250 mL
◦
3 M hydrochloric acid, HCl, 25 mL; 6 mL concentrated HCl per 25 mL
2. Student solutions
◦
0.25 M lead(II) nitrate, Pb(NO3)2, 8.3 g per 100 mL
◦
0.50 M potassium iodide, KI, 8.3 g per 100 mL
Conducting the Laboratory Activity
Pre-Lab Discussion
To review the criteria that determine when a chemical reaction has occurred,
complete the following three demonstrations (or have a student demonstrate).
Allow students to record their observations and then have them gather in small
groups (2 or 4) to discuss and answer the discussion questions.
Reaction 1: Pour 200 mL of 0.1 M Na2CO3 solution into a 500 mL beaker. Now add
200 mL of 0.1 M Ca(NO3)2 solution. The students will note the formation of a white
precipitate.
Reaction 2: Pour 200 mL of 0.02 M FeCl3 solution into a 500 mL beaker. Add 200 mL
of 0.001 M KSCN solution. Students will note the formation of a red-colored solution.
During the discussion, be sure they understand the difference between a clear but
colored solution and a colorless solution.
Reaction 3: Pour 200 mL of 0.1 M Na2CO3 solution into a 500 mL beaker. Add 25 mL
of 3 M HCl. Students will observe the evolution of a gas, which you can identify as
CO2.
Teacher/Student Interaction
During the laboratory activity observe the micropipeting technique being used. This
is a good opportunity to help students review and perfect their use of the thin-stem
pipets. During the grinding of solid samples, caution against pressing so hard that
the test tube breaks. The grinding should be a slow process so students can see the
reaction take place slowly and observe the increasing color intensity.
When students are doing Data Analysis Questions 1-5, guide their thinking by
reminding them to focus on the observations. Group work will help students draw
conclusions.
Anticipated Student Results
Part 1. Grinding of solids: As the grinding occurs, the white materials begin to turn a
yellowish color.
Part 2. Simultaneous solution addition: A line of yellow solid forms in the center of
the dish after one to two minutes.
Part 3. Delayed addition of KI: A yellow area forms near the KI immediately after it
is added.
Answers Data Analysis
1. A yellow solid forms; change of color.
2. Both systems form a yellow solid. The reaction takes longer to form in the
solution. The solid formed is not where the reactants were added.
3. Yes, the color formed was the same.
4. The color appears in a different spot. The lead(II) nitrate has had more time to
move around.
5. The materials had to move in the water before they got together.
Answers to Imply, Apply
1. The particles are very small.
2.
3. The yellow color formed indicated a different substance.
4.
5. AB + CD --> AD + CB
6. Extra AB will be left in the container.
Post-Lab Discussion
Upon completion of the follow-up questions in the Data Analysis and Imply, Apply
sections, have students gather in discussion groups to compare their answers. This
could be on the day following the laboratory activity. You may want to have them
initially answer the questions as a group depending on the degree of cooperative
learning techniques you wish to use. Encourage them to come to a group consensus.
Groups of three or four work better in this regard than groups of two. Have groups
report their findings to the rest of the class and discuss. If their conclusions are not
in agreement, repeat the reactions as a demonstration on the overhead projector
and help guide the discussion toward development of an accurate particulate model.
Students may especially need help in drawing models of the reactions (i.e., Imply,
Apply Questions 2, 4, 6).
Assessing the Laboratory Learning
Pictures in the Mind
The diagram above represents possible models of a reaction involving two solutions
like those in Parts 2 and 3 of the laboratory activity. Have your data sheet available
as you complete the evaluation. Recall that chemicals in solution often break up into
individual particles. Thus if W represents a water molecule, solute AB might break
into A and B particles and be drawn as shown in Fig. 1. In order to keep the grid
drawings simple, water molecules will be omitted for clarity, as shown in Fig. 2.
Answer the following questions by selecting the grid drawing(s) above that best
illustrate the location of the particles in the petri dish at that time in the reaction.
Use the following symbols to represent the reactants and products. (Answers given
in italics.)
Reactants AB = clear solution and
CD = clear solution
Products AD = yellow solid and
CB = remaining solution
1. uniformly distributed solution of one chemical A, D, J
2. Like Part 2 - shortly after addition of both materials H
3. Like Part 2 - 4-5 min after addition of both materials F
4. Like Part 3 - immediately after addition of the AB solution only B
5. Like Part 3 - 5 min later, but before addition of CD solution A
6. Like Part 3 - upon addition of CD solution E
7. Like Part 3 - 1 min after addition of CD solution E
8. Petri dish was moved or bumped with both AB and CD added. G, K
Written or Oral Report
Name three things you learned from this exercise that will enable you to become
more successful in the chemistry laboratory.
Answers will vary; all are acceptable. Look for comments regarding the
identification of a chemical reaction and the particulate nature of matter.
Ksp for Calcium Hydroxide
Introduction
In this experiment, you will use a measured volume of calcium hydroxide saturated
solution and neutralize it with a solution of known concentration of hydrochloric
acid. You will know when the neutralization is complete by the change in color of
the indicator in the solution. From the volume of acid used, you will be able to
determine the Ksp and the concentration of calcium hydroxide.
Procedure
1. Measure the temperature of the stock calcium hydroxide.
2. Select a Beral pipet to use for the reagents. Fill the pipet with distilled water
and then squeeze dry. Fill the pipet with the stock calcium hydroxide.
3. Carefully transfer 50 drops of calcium hydroxide to each of 3 wells in a 24
well plate. Add 2 drops of phenolphthalein to each well.
4. Empty the left over calcium hydroxide into the sink and then wash with
distilled water and squeeze dry. Fill again with distilled water and discard
the water. (Instead, you may wish to use the two-piece device consisting of a
plastic bulb and a pipet tip described above.)
5. Fill the Beral pipet with 0.1M HCl from the stock supply.
6. Add the acid to a well, counting drops and stirring until the pink color fades
away. Record the number of drops required to reach this endpoint.
7. Repeat this procedure for wells # 2 and 3.
8. Check your data. All three titrations should agree within two drops of one
another. If they do not, repeat the titration.
9. Clean your Beral pipet and your 24 well plate with distilled water.
Questions
1. Look up in the handbook the solubilities of Ca(OH)2 in water as temperature
varies. Explain in terms of energy the reasons for this trend. Does your
answer fit this trend?
2. Why is the hydroxide concentration squared in the Ksp?
3. Distinguish between the expressions dilute, concentrated, and saturated.
Which could be at a condition of equilibrium
Data Sheet
Well #1
Volume of Ca(OH)2
Volume of 0.1M HCl
Temp of Ca(OH)2
Well #2
Well #3
Data Analysis
1.
2.
3.
4.
5.
6.
7.
Calculate the average number of drops of HCl used.
Calculate the molarity of the OH- ion by using the formula: Ma x Va = Mb x Vb
Determine the molarity of calcium hydroxide.
Calculate the Ksp of calcium hydroxide. Use Ksp = [Ca2+] [OH-]2
Calculate the molarity of a saturated Ca(OH)2 solution in moles/liter.
Calculate the concentration of a saturated Ca(OH)2 solution in grams/liter.
Determine the concentration of a Ca(OH)2 saturated solution in grams/100
mL
Safety
Calcium hydroxide is caustic and hydrochloric acid is corrosive; both can cause
blindness. Wear eye protection at all times. Have an eye wash available.
Answers to Questions
1. 1.85 g/L at 0 °C; 0.77 g/L at 100 °C.
2. The hydroxide concentration is squared in the Ksp determination as there are
twice as many hydroxide particles (ions) as calcium ions. (The literature
value of Ksp depends on the reference source and the temperature. A value of
7.9 x 10-6 at 25 °C was found in a recent chemistry text.)
3. The expressions dilute, concentrated, and saturated describe the amount of
solute in a solution. A solution can only be at equilibrium with un-dissolved
solute in a saturated solution. (A saturated solution may be dilute or
concentrated.)
TG Data Table
Volume of Ca(OH)2
Volume of 0.1M HCl
Temp of Ca(OH)2
Well # 1
Well # 2
Well # 3
50
50
50
27
28
28
27°
27°
27°
Discussion
1. Calculate the average number of drops of HCl used.
(27 + 28 + 28)/3 = 28 2. Calculate the molarity of the OH- ion by using the formula
Ma x Va = Mb x Vb (0.10 M) (28 drops) = (MOH-) (50 drops) 3.
4.
5.
6.
7.
(MOH-) = (0.10 x 28)/(50) = 0.056 M Determine the molarity of calcium ion.
Ca(OH)2 --> Ca2+ + 2 OH- M Ca2+ = 0.5 x (MOH-) = 0.5 x 0.056 = 0.028 M Calculate the molarity of a saturated Ca(OH)2 solution in mol/liter.
It is the same as the M Ca2+, or 0.028 M.
Calculate the Ksp of calcium hydroxide
Ksp = [Ca2+] [OH-]2 = (0.028)(0.056)Û = 8.8 x 10-5 Calculate the concentration of a saturated Ca(OH)2 solution in gram/liter.
(0.028 mol Ca(OH)2 /L) x (74 g Ca(OH)2 / mol) = 2.07 g/L Determine the concentration of a saturated solution in gram/100 mL.
(2.07 g/L) x (1 L/1000 cm3) x (100 cm/3) = 0.21 g (per 100 cm3) Lab Hints
Prepare the saturated solution the day before the lab then filter on the day of the lab
so the students will have a clear solution.
Materials
• pulled Beral pipet (or thin stem pipets cut to 1" and tipped with a plastic pipet
delivery tip)
• 24 well plate
• tooth picks
• saturated solution of calcium hydroxide (5 g Ca(OH)2 in 100 mL of distilled water;
close to air; shake twice daily over a 1 week period; filter; store filtrate in
tightly capped bottle as limewater or saturated calcium hydroxide)
• 1% phenolphthalein indicator (dissolve 1 g phenolphthalein in 60 mL of 95%
ethanol; add enough distilled water to bring the total volume to 100 mL.)
• 0.1 M HCl (made by dissolving 9 mL of conc. HCl in 1 L of solution).
Source: http://dwb.unl.edu/Chemistry/