Cold Pack Laboratory

Certain chemicals when dissolved in water give off heat, while others become cold. These chemicals could be used in hot or cold packs. In this laboratory we will be focusing on the concept of cold packs, which can be used to reduce swelling from a bruise or injury.

A company in Hartford is trying to develop a new brand of cold packs. The cold packs will contain one chemical mixed with water. The company would like your help in determining which of the following chemicals is best for use in a cold pack, and the amount that should be used.

Ammonium chloride (NH4Cl) Calcium Chloride (CaCl2) Sodium Chloride (NaCl)

YOUR TASK You and your partners will design and conduct an experiment to determine which of three chemicals is best for use in a cold pack. After you determine which is best, try to determine the amount that should be used.

During this activity you will work with partners, but you must keep your own individual lab notes because after you finish your work you will work independently to write a report about your investigation.

You have been provided with the following materials and equipment. It may not be necessary to use all of the materials and equipment that has been provided. You may use additional materials and equipment if they are available:

0-20 g Ammonium chloride Teaspoons 0-20g Calcium chloride 0-20 g Sodium Chloride Stirrers Plastic cups 1 graduated cylinder Access to an electronic balance 3 thermometers Access to a watch or clock with a second hand Vinyl gloves Splash-proof goggles and safety aprons Paper towels Access to water STEPS TO FOLLOW 1. In your own words, clearly state the problem you are going to investigate. Include a clear identification of the independent and dependent variables that you will study. Write your statement of the problem in your notebook.

2. Design an experiment to solve your problem. Only use the amount of chemicals you have been given. Your experimental design should match the statement of the problem, should control for all variables, and should be clearly described so that a stranger could easily replicate your experimental procedures without any confusion. Include a control if appropriate. CAUTION: DO NOT MIX THE CHEMICALS TOGETHER. 3. Write you experimental procedures in your notebook. Show your procedures to your teacher before you begin your experiments.

4. After receiving approval from your teacher, work with your partners to carry out your experiment. Your teacher’s approval does not necessarily mean that your teacher thinks that your experiment is well-designed. It simply means that in your teacher’s judgement your experiment is not dangerous or likely to cause an unnecessary mess.

5. While conducting your experiments, take notes in your notebook. Include the data from your experiment. All data should be organized in tables, charts, and/or graphs, which should be properly labeled and titled.

Your notes will not be scored, but they will be helpful to you later when you work independently to write about your experiment and results. You must keep your own lab notes because you won’t work with your partners when you write up your lab report.

When you have finished your experiment, your teacher will give you instructions for cleanup procedures including the proper disposal of all materials.

DIRECTIONS FOR WRITING YOUR LAB REPORT

Working on your own, summarize your experiment and results. You may use the notes that you took while working with your partners. Your report should include the following:

 A clear statement of the problem you investigated. Include a clear identification of the independent and dependent variables that you studied.  A description of the experiment you carried out. Your description should be clear and complete enough so that someone else could easily replicate your experiment.  The results of your experiment. Tables, charts, and/or graphs should be indicated where appropriate and should be properly titled and labeled.  Your conclusions from your experiment. Your conclusions should be fully supported by your data.  Comments about how valid you think your conclusions are. In other words, how much confidence do you have in your results and your conclusions? Any factors that contribute to a lack of confidence in your results or conclusions should be discussed. Also, include ways that your experiment could be improved if you were to do it again.