Démonstration de Réaction Endothermique

Réaction froide entre l'hydroxyde de baryum et le thiocyanate d'ammonium

Thermochemistry Intermediate (High School) 20 min ~$12,00

Objectif

Démontrer une réaction remarquablement endothermique où le mélange devient suffisamment froid pour congeler l'eau à l'extérieur du flacon.

Contexte

When barium hydroxide octahydrate reacts with ammonium thiocyanate, the temperature drops to approximately -20°C. This endothermic reaction absorbs so much heat from the surroundings that water on the outside of the flask freezes, effectively gluing the flask to a wet board.

Avertissements de sécurité

  • Barium compounds are toxic if ingested
  • Ammonia gas is released — work in fume hood or ventilated area
  • Wear gloves when handling barium hydroxide
  • Do not inhale the ammonia fumes

EPI requis

goggles gloves lab_coat

Matériaux

  • Barium hydroxide octahydrate (32 g)
    Toxic
  • Ammonium thiocyanate (16 g)
  • Water (5 mL)
    On the board

Équipement

250 mL Erlenmeyer flask Wooden board Thermometer Stirring rod

Procédure

1

Pour a few drops of water onto the wooden board to create a wet spot.

1 min
2

Add 32 g barium hydroxide octahydrate to the flask.

2 min Wear gloves — barium is toxic
3

Add 16 g ammonium thiocyanate to the flask. Stir the mixture with a glass rod.

2 min Ammonia released — ventilation
4

Place the flask on the wet spot on the board. Insert the thermometer.

1 min
5

Observe the temperature dropping dramatically. Record the minimum temperature.

5 min Do not inhale fumes
6

After 5 minutes, try to lift the flask. It should be frozen to the board.

2 min
7

Explain that the reaction absorbed heat from the surroundings, freezing the water beneath.

2 min

Résultats attendus

The temperature should drop to approximately -20°C within minutes. The flask should freeze to the wet board. A strong smell of ammonia confirms the reaction is proceeding.

Nettoyage

Allow to warm to room temperature. Dispose of barium waste in heavy metal waste container. Rinse flask and ventilate area thoroughly.

Détails

Catégorie
Thermochemistry
Difficulté
Intermediate (High School)
Durée
20 min
Coût estimé
$12,00
Étapes
7
Matériaux
3

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Frequently Asked Questions

What is the objective of Démonstration de Réaction Endothermique?
Démontrer une réaction remarquablement endothermique où le mélange devient suffisamment froid pour congeler l'eau à l'extérieur du flacon.
How difficult is Démonstration de Réaction Endothermique?
This experiment is rated as Intermediate (High School). It takes approximately 20 minutes to complete.
What safety precautions are needed for Démonstration de Réaction Endothermique?
Key safety precautions include: Barium compounds are toxic if ingested; Ammonia gas is released — work in fume hood or ventilated area; Wear gloves when handling barium hydroxide.
What materials are needed for Démonstration de Réaction Endothermique?
The main materials required are: Barium hydroxide octahydrate, Ammonium thiocyanate, Water.
What results should I expect from Démonstration de Réaction Endothermique?
The temperature should drop to approximately -20°C within minutes. The flask should freeze to the wet board. A strong smell of ammonia confirms the reaction is proceeding.