Freezing Point Depression

Materials

• Digital readout voltmeter
• Temperature probe
• 400 mL beaker
• Trough
• Ice water
• Salt

Procedure

1. Connect the temperature probe to the voltmeter.
2. Place the beaker in the trough and fill them both half full with ice & water.
3. Place the temperature probe in the beaker of ice water and wait until the temperature registers 0ºC.
4. Pour a lot of salt into the beaker of ice water and stir. The temperature will drop and ice in the trough will freeze to the outside of the beaker.

Discussion

If salt is added until the solution is saturated (23% aq. solution), the freezing point depression is nearly 21ºC. Ice on frozen sidewalks and roads will melt if salt is sprinkled on top because the salt depresses the freezing point of water.