L. Knight
2010
Name ____________________________
date ___________
Hot Pack/Cold Pack Lab
Background
Heat of Solution is the energy involved when a salt is dissolved into water. The heat
of solution is different for each different salt that is dissolved.
In this lab you will determine the heat of solution for four unknown salts (labeled A,
B, C, D). From this data you will determine which substance is the best cold pack
chemical and which is the best hot pack chemical. The substance with the largest
increase in temperature per gram of salt will make the best hot pack. The
substance with the largest decrease in temperature per gram of salt will make the
best cold pack.
Procedure
HINT: Precision in measuring is IMPORTANT!! Make sure you record your data to
the correct number of digits!
1) Add 50.0 mL of deionized water to the calorimeter.
2) Put a weighing boat on the balance, then zero the balance and put
approximately 3.0g of a salt into the boat.
3) Transfer the salt to a clean and dry mortar and pestle and crush to a powder.
4) Put your original weighing boat back on the balance, zero the balance, then
transfer the salt back to the boat to record the mass.
5) Record the initial temperature of the water in the calorimeter.
6) Pour the salt from the weighing boat into the calorimeter water.
7) Use the thermometer to stir the solution. You want to dissolve the salt as quickly
as possible. You may have to use a stirring rod to break up clumps.
YOU MAY USE THE THERMOMETER TO STIR, BUT NOT TO BREAK UP CLUMPS!!
8) While you are stirring, keep the cup on the bench and be sure to hold the cup
from the top (so your hands do not influence the temperature of the solution).
9) Record the highest (or lowest) temperature that is reached after the salt is
completely dissolved. (NOTE: You may have to keep stirring and watching the
thermometer for a few minutes after the salt is dissolved.)
10)Rinse out the calorimeter. Waste may go down the drain for this lab.
11)Repeat the procedure for the other 3 salts. You may test the salts in any order.
L. Knight
2010
Data
Salt A
Salt B
Salt C
Salt D
mass of salt
(after crushing)
(g)
temp. of water
before (ºC)
temp. of water
after (ºC)
Calculations
1) For each salt, determine the effectiveness of each salt in terms of change in ºC
per gram of salt. (initial temp. - final temp.) Be sure to show all work, circle
your final answer and include units in your final answer!
Salt A
change in temp.
change in temp./gram of salt
Salt B:
change in temp.
change in temp./gram of salt
L. Knight
2010
Salt C:
change in temp.
change in temp./gram of salt
Salt D:
change in temp.
change in temp./gram of salt
Questions
1) Which salt would make the most effective hot pack?
_________
Why?
2) Which salt would make the most effective cold pack?
Why?
_________
L. Knight
2010
3) For the most effective hot pack, was the change in energy positive or negative?
__________________________________________
Therefore, which had more energy? (circle one)
reactants
products
How do you know?
This reaction was (circle one)
exothermic
endothermic
4) For the most effective cold pack, was the change in energy positive or
negative?
__________________________________________
Therefore, which had more energy? (circle one)
reactants
products
How do you know?
This reaction was (circle one)
exothermic
endothermic
5) In your own words what are two differences between exothermic and
endothermic reactions?
a) ___________________________________________________________
__________________________________________________________________
__________________________________________________________________
b) ___________________________________________________________
__________________________________________________________________
__________________________________________________________________