Name:
Group Members:
Hot Pack or Cold Pack Procedure – First Draft
With your lab group, construct and write a very detailed procedure in numbered steps and full
sentences, for 1 trial, using the same setup as in the Hess’ Law Lab, to determine the change in
temperature that results when a certain mass of ionic solid dissolves in a certain volume of water. All
the equipment must be mentioned
 You must be as specific as possible – because another group will use your procedure to perform
the lab. The group can identify the equipment, but does not know how to use them.
The ideal hand warmer or cold pack changes in temperature by 20oC (but no more) as quickly as
possible, has a volume of about 50 mL, and uses 10 grams of an ionic solid or less. It costs as little as
possible to make, and uses chemicals that are as safe and environmentally friendly as possible.
_____________________________________________________________________________________
Score: (from rubric) _________ out of 4
Comments: (Written by the other group who will read this procedure)
Name:
Group Members:
Designing a Hot Pack or Cold Pack Lab
A. Experimental Overview
The purpose of this lab is to design an effective hot pack OR cold pack that is inexpensive, nontoxic, and
safe for the environment.
The ideal hot pack or cold pack changes in temperature by 20oC (but no more) as quickly as possible,
has a volume of about 50 mL, and uses 10 grams or less of an ionic solid. It costs as little as possible to
make, and uses chemicals that are as safe and environmentally friendly as possible.
Our group has to determine which salt is the best: (circle) –
hot pack
OR
cold pack
Read This! Safety and Cost Information
Material Safety Data Sheets (MSDS): See your teacher’s website. These are sheets that detail safety
and hazard information for each of the six chemicals.
Safety Precautions
Ammonium nitrate is a strong oxidizer and may explode if heated under confinement. It is also
slightly toxic by ingestion and a body tissue irritant. Calcium chloride is slightly toxic. Lithium chloride
is moderately toxic by ingestion. Magnesium sulfate is a body tissue irritant. Sodium acetate is a
body tissue and respiratory tract irritant. Avoid contact of all chemicals with eyes and skin. Wear
chemical splash goggles, chemical-resistant gloves, and a chemical apron. Wash hands thoroughly
with soap and water before leaving the laboratory.
Cost of Each Solid:
Solid
NH4NO3
Cost ($)/kg
18.50
CaCl2
10.80
KCl
30.00
NH4Cl
1.67
Na2CO3
5.95
NaNO3
20.00
Read This! A Note on the Sign of q
In the Hess’ Law Lab and in this lab (and indeed in all calorimetry procedures involving aqueous
solutions), the water that makes up most of the solution counts as the surroundings, not as the
system. The system consists of the solids and the ions that form when the solids dissolve in the
water. Thus, your temperature probe really measures temperature change in the surroundings, not
in the system.
What this means is that an exothermic reaction will release heat into the surroundings and the
surroundings will increase in temperature accordingly. An exothermic reaction will have a negative
value of qsystem. Conversely, an endothermic reaction will have a positive value of qsystem and register a
decrease in temperature, since the surroundings is losing heat.
Name:
Group Members:
Procedure
Write your polished and revised procedure here in numbered steps and complete sentences. Use the
comments from your group’s first draft to write the clearest procedure possible for the lab.
Data Tables for 6 Ionic Compounds (you will be assigned three to do; run each solid two times)
Show all work and calculations. Use sig fig conventions and a unit after every answer. Keep in mind that
exothermic reactions will show an increase in temperature and the sign of q or ΔH will be negative.
A. Data for Your Three Assigned Salts
T1: Salt(1)
Salt
Formula
Mass of
Water (g)
Mass of
Salt (g)
Total
Mass (g)
Initial
Temp (C)
Final
Temp (C)
T1: Salt(2)
T1: Salt(3)
Name:
Group Members:
Calculations For Your Three Assigned Salts:
T1: Salt(1)
T1: Salt (2)
T1: Salt (3)
Calculate
qsoln in kJ
C=
4.184
J/(g·°C)
Calculate
# of moles
of your
salt
Calculate
ΔHsoln in
kJ/mol of
salt
B. Data for The Other Three Salts (from another group)
T1: Salt(1)
T1: Salt(2)
Salt
Formula
Mass of
Water (g)
Mass of
Salt (g)
Total
Mass (g)
Initial
Temp (C)
Final
Temp (C)
Calculated
ΔHsoln in
kJ/mol of
salt
T1: Salt(3)
Name:
Group Members:
Answer each analysis question in complete, grammatically correct sentences.
1.
What possible sources of error could affect the accuracy of your calculated value of the amount of solid in
your hot pack or cold pack? List at least two and what effect they would have on the temperature
change.
2.
Based on the calculated Hsoln for each of the six solids, the cost per kg of each solid, and
information in the MSDS sheets for each chemical (available on your teacher’s website), which
of the six solids makes the most effective, safe, environmentally benign and inexpensive hot
pack or cold pack (whichever one you were assigned)? Address each of these four concerns in
your explanation below, use evidence to back up your ideas, then thoughtfully answer this
question.