The temperature at which a liquid turns into a solid is called its freezing point. Different liquids have different freezing points. Also, dissolving a substance in a liquid affects its freezing point, making it lower.

In this project, you will investigate the freezing points of several liquids.

Materials

• 1 marking pen
• 1 tall, narrow glass container (an olive jar or baby bottle is ideal)
• 1 plastic bowl, can, or other container, two to three times wider than the glass container
• 1 thermometer
• ice
• salt
• several test liquids, such as milk, salt water, rubbing alcohol, vinegar, and water
• record sheet

Procedure

1. Draw a mark on the glass container to indicate filling level (about one-half to three-quarters full).
2. Fill to the mark with one test liquid.
3. Set the glass container in the bowl or can.
4. Insert the thermometer vertically into the test liquid.
5. Fill the bowl or can with ice.
6. Pour salt on the ice. Be careful not to get it in your test liquid.
7. Place the experiment in the freezer. Check it at three- to five-minute intervals, removing it as soon as it appears to begin freezing. Record its temperature.
8. Rinse the glass and dry it.
9. Repeat Steps 2 through 8 with several other test liquids. You may use the same container of ice and salt each time, adding more as needed.

Drawing Conclusions
Did each liquid freeze at the same temperature, or at a different temperature? Did any of the liquids you tested freeze at the point usually considered "freezing" (32°F (0°C)—the freezing point of pure water)? How would you explain the reasons for the differences? Were there any test liquids that did not freeze?

Extension

You can expand this project for a science fair by first predicting the freezing point of each liquid and then testing your hypothesis. You could also test different concentrations of salt solution and measure their freezing points. Is there a relationship between concentration and freezing point?

This article is from Projects: Science by Steck-Vaughn, a Harcourt Company.