Freezing Point Depression and Heat of Solution

Purpose:

To demonstrate the freezing point depression of a solution, along with the concepts of heat of solution and entropy.

Materials:

• 2 Styrofoam cups
• 2 Thermometers

Reagents:

• 9M Sulfuric acid (H₂SO₄)
• Ice

Hazards and PPE:

• Sulfuric acid is acutely corrosive and toxic. Avoid skin contact and inhalation of fumes.
• Wear approved safety goggles and gloves.

Protocol:

Demonstration

1. Place 100g DI H₂O in one cup and 100g ice in the other. Place a thermometer in each and read off the temperatures.
2. Pour 100mL H₂SO₄ into each cup. Read off the new temperatures of each.
   1. The heat of solution should cause the acid-water cup to increase in temperature to ~20 C.
   2. The freezing point depression of the solution should cause the temperature of the acid-ice cup to decrease to about -15 C. The heat generated will melt the ice.

Disposal:

• Solutions can be diluted and poured down the drain with excess water.

Citations:

1. Summerlin, L., Borgford, C., & Ealy J. Chemical Demonstrations: A Sourcebook for Teachers, Volume 2, Second Edition, 1988.

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