Unit: Solutions
Chemistry, Wilson
The Chemistry of Hot and Cold Packs
Purpose: To design a lab that will allow us to
determine the molarity and heat of solution of hot
and cold packs.
Theory: Hot and Cold packs are made by placing a
sealed bag of solid salt (remember salt is a metal and
nonmetal that combine with an ionic bond) into a bag
of water. When the cold or hot packs are needed,
the athletic trainer will squeeze the bag and empty the
contents of salt into the water. In return the
dissolving of the salt will either generate or absorb heat.
Materials
 Graduated Cylinder
 Distilled Water
 Thermometer
 Calorimeter
 5.00g of MgSO4 Crystals
 5.00g of NH4NO3
Procedure
 Design your own lab that will allow you to achieve the purpose.
 Remember calorimetry uses the change of temperature, not the highest temperature.
Data Table
 Create Your Own
 You need to know the mass of water you use for each part
Calculations
 Heat of Solution for both MgSO4 and NH4NO3
 The number of moles used for MgSO4 and NH4NO3 solutions
 Find the kJ/mol absorbed or released for each MgSO4 and NH4NO3 solutions
 Molarity of Each Solution
 Percent Error of Heat of Solutions
Conclusions
 Which salt is used as an ice pack? Which salt is used as a hot pack?
 For each of the questions above, explain whether energy is either given off to the environment or
absorbed from the environment. Which one is exothermic and which is endothermic?
Needed Equations/Information
 Specific Heat Formula
 Heat of Solution NH4NO3 = 26.2 kJ/mol
 Heat of Solution MgSO4 = 1278 kJ/mol