AP Inquiry Experiment 12: The Hand Warmer Design Challenge
Central Challenge
You are challenged to use chemistry to design an effective, safe, environmentally benign, and inexpensive hand warmer. The ideal hand warmer increases in temperature by 20°C (but no more) as quickly as possible, has a volume of about 50 mL, costs as little as possible to make, and uses chemicals that are as safe and environmentally friendly as possible. Students will carry out an experiment to determine which substances, in what amounts, to use in order to make a hand warmer that meets these criteria.
Context for This Investigation
Have your fingers ever been so cold they felt numb? Wouldn’t it be great if you could generate heat to warm your hands up anytime you want to? That’s exactly what a “hand warmer” does. One type of hand warmer contains water in one section of the packet and a soluble substance in another section. When the packet is squeezed the water and the soluble substance are mixed, the solid dissolves and the packet becomes warm. In this experiment, students will learn how a hand warmer works and use chemistry to design an effective, safe, environmentally benign, and inexpensive hand warmer. You will dissolve salts in water to see their effect on the temperature.
PrelabWrite a purpose for this lab.
Look up the hazard warnings, and disposal information for all chemicals used in the lab.
Salts to be tested potassium chloridecopper sulfatesodium acetate magnesium sulfatecalcium chloridesodium carbonate
■Investigation
Design and execute an experimental procedure to determine which of the ionic compounds is most suitable for use in a hand warmer. Review the criteria for an ideal hand warmer from the Central Challenge. For each solid, consider safety, cost, and environmental impact as well as the amount of heat released or absorbed.
Write down the procedure you will follow. Explain it to your instructor before you proceed. This needs to be included in your post lab.
Things to keep in mind
1. Safety and Environmental Impact: Obtain the MSDS for your solids. Review each one, making notes about safety concerns, necessary precautions, and disposal.
3. Cost:
Substance 2012 Cost per 500 g ($)
CaCl2 6.55CuSO445.65MgSO432.70
NaC2H3O2 12.90Na2CO3 6.15KCl 4.50
3. Heat of Solution: Work with your group to design a procedure to compare the solids in terms of the heat released or absorbed when they dissolve and include what materials and equipment you will use. You must include the safety precautions you will take.
Important Procedural Tips
1. Be sure to keep detailed records of the amounts of substances used and the starting and ending temperature as you will need it later to determine the amount of solid to use in your hand warmer.
2. You will receive a maximum of 10 g of each solid for this part.
3. Nest the Styrofoam cup in a beaker, it will tip over if you don’t. Keeping a lid on the cup will give you better results.
Data Collection and Computation
You now need to calculate the change of enthalpy of dissolution (also called the “heat of solution,” with symbol ΔHsoln, and units of kJ/mol solute) occurring in aqueous solution. The data necessary to calculate the heat of solution can be obtained using a calorimeter. Calorimeter Constant Determination: According to the law of conservation of energy, energy cannot be created or destroyed, only changed from one form to another or transferred from one system to another. The temperature change observed when water or any substance changes temperature can be a result of a transfer of energy
