An instant cold pack usually consists of a rugged plastic bag with water and a soluble compound inside. The water is sealed in a fragile inner bag to keep it separated from the solid. When the cold pack is needed, it is squeezed to break open the inner container and bring the water and solid together. As the water and solid interact, heat is absorbed and temperature decreases.
Ammonium nitrate, NH4NO3, has been the solid most often used in instant cold packs. But, because it is much less hazardous, urea, (NH2)2CO, is replacing ammonium nitrate for this use. In this experiment, you will investigate the properties of urea and urea-containing cold packs.
In the Preliminary Activity, you will gain experience using a Temperature Probe as you determine the temperature change as a sample of urea dissolves in water.
After completing the Preliminary Activity, you will first use reference sources to find out more about cold packs, urea, and heat before you choose and investigate a researchable question dealing with urea or urea-containing cold packs.
Sensors and Equipment
This investigation requires each of the following Vernier sensors and equipment (unless otherwise noted):
Step-by-step instructions for the Preliminary Activity
List of materials and equipment
Note: The experiment preview of the Preliminary Activity does not include essential teacher information, safety tips, or sample data. Instructions for Logger Pro and other software (such as LabQuest App or TI handheld software, where available) are on the CD that accompanies the book. We strongly recommend that you purchase the book before performing experiments.