Hand Warmer Design Challenge

Background

 Chemical hand warmers are an effective, and environmentally safe way of producing heat.

 They are made by using the heat of solvation of soluble ionic compounds.

 The ideal hand warmer:  Should increase in temperature by 20 o C as quickly as possible  Has a volume of about 50 mL  Costs as little as possible to make  Uses chemicals that are as environmentally friendly as possible.

 Your objective is to determine which substance would be the best for making hand warmers.

Substance

NaCl CaCl 2 Na 2 CO 3 LiCl NH 4 Cl

Cost per 500 g ($)

3.95

6.55

6.15

32.75

9.05

Materials

 You will need many of the same materials we used in Advanced Lab Skills when learning about Calorimetry.  You might need more.

 Make sure you include any materials you use in your lab report.  Your will receive only 10.0 g of each substance.

Safety

 Safety is a big part of this lab.  Part of your decision about what substance to use should be the safety considerations of the substances.

 A substance that produces a lot of heat, but poses significant health risks, might not be a good selection.

 You will use Flinn Scientific’s MSDS data base to collect safety data for the five substances we will be using.

 http://www.flinnsci.com/msds-search.aspx

Procedure/Data

 It will be up to you to come up with a procedure and data table for this lab.

 Use your notes from our Advance Lab Skills calorimetry activity.

 When designing your procedure and data table keep in mind that we are trying to determine.

 The first thing you are going to do is determine the calorimeter constant.

 Make sure you keep track of how much of each substance you use in each trial of your experiment. You need to record the EXACT mass of the sample you dissolve.

 Remember you will only get 10 g of each substance so use it wisely, don’t use it all at once, you might want to do more than one trial.

Analysis Questions

1.

2.

3.

4.

5.

Using the information provided in the background section calculate the cost per hand warmer of each of the possible substances. 6.

Show all of your work for your calculations of C cal Create table that includes the following calculated quantities. (Show all calculations as well). Do all calculations of all trials. You will report the average ΔH sol for both trials.

Which compounds, if any, can you eliminate as possible choices? Why?

Of the possible compounds that could be used for your hand warmer, calculate the amount in grams that would be needed to increase the temperature of 50 mL of water by 20 o C.

Write a paragraph stating which compound you would use to create the ideal hand warmer. Include all of the considerations such as, environmental safety, cost, and ability to increase in temperature.