Demonstration einer endothermen Reaktion

Kalte Reaktion von Bariumhydroxid und Ammoniumthiocyanat

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

Ziel

Eine drastisch endotherme Reaktion demonstrieren, bei der das Gemisch so kalt wird, dass es Wasser an der Außenseite des Kolbens gefrieren lässt.

Hintergrund

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.

Sicherheitswarnungen

  • 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

Erforderliche PSA

goggles gloves lab_coat

Materialien

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

Ausrüstung

250 mL Erlenmeyer flask Wooden board Thermometer Stirring rod

Durchführung

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.

Erwartete Ergebnisse

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.

Aufräumen

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

Details

Kategorie
Thermochemistry
Schwierigkeit
Intermediate (High School)
Dauer
20 Min.
Geschätzte Kosten
$12,00
Schritte
7
Materialien
3

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Frequently Asked Questions

What is the objective of Demonstration einer endothermen Reaktion?
Eine drastisch endotherme Reaktion demonstrieren, bei der das Gemisch so kalt wird, dass es Wasser an der Außenseite des Kolbens gefrieren lässt.
How difficult is Demonstration einer endothermen Reaktion?
This experiment is rated as Intermediate (High School). It takes approximately 20 minutes to complete.
What safety precautions are needed for Demonstration einer endothermen Reaktion?
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 Demonstration einer endothermen Reaktion?
The main materials required are: Barium hydroxide octahydrate, Ammonium thiocyanate, Water.
What results should I expect from Demonstration einer endothermen Reaktion?
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.