Supersaturation and Instant Crystallization

Triggering instant crystal formation in sodium acetate

Crystallization Intermediate (High School) 35 min ~$8.00

Objective

Prepare a supersaturated sodium acetate solution and trigger instantaneous crystallization, demonstrating metastable supersaturation and exothermic crystallization (hot ice).

Background

Sodium acetate trihydrate can form extremely supersaturated solutions that remain liquid until disturbed. Adding a single seed crystal or scratching the container wall triggers rapid crystallization throughout the solution, releasing heat (exothermic). The resulting solid resembles ice but is warm to the touch.

Safety Warnings

  • The solution gets hot when it crystallizes — handle with care
  • Sodium acetate is generally safe but avoid ingestion
  • Use heat-resistant gloves when handling hot solution

Required PPE

goggles

Materials

  • Sodium acetate trihydrate (100 g)
    Or make from vinegar + baking soda
  • Distilled water (10 mL)
    Minimal amount

Equipment

250 mL beaker or flask Hot plate Stirring rod Thermometer

Procedure

1

Add 100 g sodium acetate trihydrate and 10 mL water to the beaker. Heat while stirring until all crystals dissolve (about 70°C).

8 min Handle hot solution carefully
2

Remove from heat and allow to cool to room temperature undisturbed. Do not shake or add anything.

15 min
3

Once cooled, the solution should remain liquid despite being supersaturated. Measure the temperature.

2 min
4

Drop a single small crystal of sodium acetate into the solution and observe the rapid crystallization wave.

2 min
5

Immediately measure the temperature of the newly formed crystals. Note the temperature increase (exothermic).

2 min Crystals will be warm
6

The process is reversible — reheat to dissolve and repeat.

5 min

Expected Results

When triggered, crystallization should sweep through the solution in seconds, forming a solid mass of warm crystals (hence "hot ice"). The temperature typically rises 10-20°C above room temperature. This is the principle behind reusable hand warmers.

Cleanup

Sodium acetate is reusable. Simply reheat to dissolve. Can be disposed down the drain. Rinse equipment.

Details

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

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Frequently Asked Questions

What is the objective of Supersaturation and Instant Crystallization?
Prepare a supersaturated sodium acetate solution and trigger instantaneous crystallization, demonstrating metastable supersaturation and exothermic crystallization (hot ice).
How difficult is Supersaturation and Instant Crystallization?
This experiment is rated as Intermediate (High School). It takes approximately 35 minutes to complete.
What safety precautions are needed for Supersaturation and Instant Crystallization?
Key safety precautions include: The solution gets hot when it crystallizes — handle with care; Sodium acetate is generally safe but avoid ingestion; Use heat-resistant gloves when handling hot solution.
What materials are needed for Supersaturation and Instant Crystallization?
The main materials required are: Sodium acetate trihydrate, Distilled water.
What results should I expect from Supersaturation and Instant Crystallization?
When triggered, crystallization should sweep through the solution in seconds, forming a solid mass of warm crystals (hence "hot ice"). The temperature typically rises 10-20°C above room temperature. This is the principle behind reusable hand warmers.