Exothermic Crystallization of Sodium Acetate

Measuring the heat released during instant crystallization

Thermochemistry Intermediate (High School) 30 min ~$8.00

Objective

Quantify the heat released during the crystallization of supersaturated sodium acetate using calorimetry.

Background

When supersaturated sodium acetate crystallizes, it releases stored energy as heat. By triggering crystallization inside a calorimeter and measuring the temperature rise, the enthalpy of crystallization can be determined. This is the same principle used in reusable hand warmers.

Safety Warnings

  • Hot solution during preparation
  • Crystallization releases heat — container gets warm

Required PPE

goggles

Materials

  • Sodium acetate trihydrate (80 g)
  • Distilled water (150 mL)

Equipment

Polystyrene cup calorimeter Hot plate Thermometer Beaker (250 mL) Stirring rod

Procedure

1

Dissolve 80 g sodium acetate trihydrate in 20 mL water by heating to about 70°C. Stir until clear.

8 min Handle hot solution carefully
2

Pour the solution into the polystyrene cup calorimeter. Allow to cool undisturbed to room temperature.

15 min
3

Record the temperature of the supersaturated solution.

1 min
4

Add a single small crystal of sodium acetate to trigger crystallization. Immediately stir gently and record temperature every 15 seconds.

3 min
5

Record the maximum temperature reached.

1 min
6

Calculate the heat released: q = mcΔT. Determine ΔH of crystallization per mole.

5 min

Expected Results

Temperature should rise 15-25°C above room temperature. The enthalpy of crystallization is approximately -19.7 kJ/mol for sodium acetate trihydrate. Measured values should be within 20% of this.

Cleanup

The sodium acetate can be remelted and reused. Rinse the calorimeter. Non-toxic — can go down the drain.

Details

Category
Thermochemistry
Difficulty
Intermediate (High School)
Duration
30 min
Est. Cost
$8.00
Steps
6
Materials
2

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Frequently Asked Questions

What is the objective of Exothermic Crystallization of Sodium Acetate?
Quantify the heat released during the crystallization of supersaturated sodium acetate using calorimetry.
How difficult is Exothermic Crystallization of Sodium Acetate?
This experiment is rated as Intermediate (High School). It takes approximately 30 minutes to complete.
What safety precautions are needed for Exothermic Crystallization of Sodium Acetate?
Key safety precautions include: Hot solution during preparation; Crystallization releases heat — container gets warm.
What materials are needed for Exothermic Crystallization of Sodium Acetate?
The main materials required are: Sodium acetate trihydrate, Distilled water.
What results should I expect from Exothermic Crystallization of Sodium Acetate?
Temperature should rise 15-25°C above room temperature. The enthalpy of crystallization is approximately -19.7 kJ/mol for sodium acetate trihydrate. Measured values should be within 20% of this.