吸热反应演示

氢氧化钡与硫氰酸铵的冷却反应

Thermochemistry Intermediate (High School) 20 分钟 ~$12.00

目标

演示一个剧烈吸热反应，混合物冷却程度足以使烧瓶外表面的水结冰。

背景

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.

安全警告

  • 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

所需PPE

goggles gloves lab_coat

材料

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

设备

250 mL Erlenmeyer flask Wooden board Thermometer Stirring rod

步骤

1

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

1 分钟
2

Add 32 g barium hydroxide octahydrate to the flask.

2 分钟 Wear gloves — barium is toxic
3

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

2 分钟 Ammonia released — ventilation
4

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

1 分钟
5

Observe the temperature dropping dramatically. Record the minimum temperature.

5 分钟 Do not inhale fumes
6

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

2 分钟
7

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

2 分钟

预期结果

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.

清理

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

详情

类别
Thermochemistry
难度
Intermediate (High School)
时长
20 分钟
预估费用
$12.00
步骤数
7
材料
3

更多实验

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Frequently Asked Questions

What is the objective of 吸热反应演示?
演示一个剧烈吸热反应，混合物冷却程度足以使烧瓶外表面的水结冰。
How difficult is 吸热反应演示?
This experiment is rated as Intermediate (High School). It takes approximately 20 minutes to complete.
What safety precautions are needed for 吸热反应演示?
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 吸热反应演示?
The main materials required are: Barium hydroxide octahydrate, Ammonium thiocyanate, Water.
What results should I expect from 吸热反应演示?
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.