The Science Behind a Cold Pack

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Updated on Apr 10, 2014


This science project explores endothermic reactions by comparing the temperature change that results from various chemicals added to water.

Research Questions:

  • How do cold packs work?
  • In chemistry, what happens during an endothermic reaction?
  • Which substance cools off water the most: baking soda, sour salt, Morton Lite, washing soda, or a deicer?

Did you ever wonder what is inside of a cold pack? You can make a basic cold pack by mixing a salt (such as potassium chloride) or soda (such as baking soda) with water. Mixing the two creates a chemical reaction that uses up energy, which makes the mixture colder. You can see which substance cools off water the most by trying out this experiment.


  • Tap water
  • Measuring cup
  • Cup
  • Sodium bicarbonate (baking soda)
  • Citric acid (sour salt)
  • Potassium chloride (Morton Lite)
  • Sodium carbonate (washing soda)
  • Calcium chloride (deicer)

Experimental Procedure

1. Pour ½ cup of tap water into a cup.

2. Stir the cup with a thermometer and record the temperature.

3. Add four teaspoons of sodium bicarbonate to the water and stir with the thermometer. Record the resulting temperature.

4. Subtract the temperature from Step 2 from the temperature in Step 3. This will give you the change in temperature.

5. Record your data in a chart, such as the one below.

Chemical Added

Original Temperature

Final Temperature

Temperature Change

6. Wash the cup and thermometer and dry them well.

7. Repeat this process with the citric acid, potassium chloride, sodium carbonate, and calcium chloride. Record all data.

8. Analyze your data. Which of the substances would create the best cold pack?

Terms/Concepts: Endothermic reaction; Ions


First Place Science Fair Projects for Inquisitive Kids, by Elizabeth Snoke Harris. Pp. 96-97.

Keren Perles has worked as an educational writer, editor, teacher, and tutor of all ages. Her experience spans the subject areas, from science and math, to English and the Hebrew language.

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