Sursaturation et Cristallisation Instantanée

Déclenchement de la formation instantanée de cristaux dans l'acétate de sodium

Crystallization Intermediate (High School) 35 min ~$8,00

Objectif

Préparer une solution sursaturée d'acétate de sodium et déclencher la cristallisation instantanée, démontrant la sursaturation métastable et la cristallisation exothermique (glace chaude).

Contexte

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.

Avertissements de sécurité

  • 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

EPI requis

goggles

Matériaux

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

Équipement

250 mL beaker or flask Hot plate Stirring rod Thermometer

Procédure

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

Résultats attendus

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.

Nettoyage

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

Détails

Catégorie
Crystallization
Difficulté
Intermediate (High School)
Durée
35 min
Coût estimé
$8,00
Étapes
6
Matériaux
2

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Frequently Asked Questions

What is the objective of Sursaturation et Cristallisation Instantanée?
Préparer une solution sursaturée d'acétate de sodium et déclencher la cristallisation instantanée, démontrant la sursaturation métastable et la cristallisation exothermique (glace chaude).
How difficult is Sursaturation et Cristallisation Instantanée?
This experiment is rated as Intermediate (High School). It takes approximately 35 minutes to complete.
What safety precautions are needed for Sursaturation et Cristallisation Instantanée?
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 Sursaturation et Cristallisation Instantanée?
The main materials required are: Sodium acetate trihydrate, Distilled water.
What results should I expect from Sursaturation et Cristallisation Instantanée?
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.