Demonstração de Reação Endotérmica

Reação fria de hidróxido de bário e tiocianato de amônio

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

Objetivo

Demonstrar uma reação dramaticamente endotérmica onde a mistura se torna fria o suficiente para congelar a água na parte externa do frasco.

Contexto

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.

Avisos de segurança

  • 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 necessário

goggles gloves lab_coat

Materiais

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

Equipamentos

250 mL Erlenmeyer flask Wooden board Thermometer Stirring rod

Procedimento

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

Resultados esperados

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.

Limpeza

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

Detalhes

Categoria
Thermochemistry
Dificuldade
Intermediate (High School)
Duração
20 min
Custo estimado
$12,00
Passos
7
Materiais
3

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Frequently Asked Questions

What is the objective of Demonstração de Reação Endotérmica?
Demonstrar uma reação dramaticamente endotérmica onde a mistura se torna fria o suficiente para congelar a água na parte externa do frasco.
How difficult is Demonstração de Reação Endotérmica?
This experiment is rated as Intermediate (High School). It takes approximately 20 minutes to complete.
What safety precautions are needed for Demonstração de Reação Endotérmica?
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 Demonstração de Reação Endotérmica?
The main materials required are: Barium hydroxide octahydrate, Ammonium thiocyanate, Water.
What results should I expect from Demonstração de Reação Endotérmica?
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.