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AND NOW…THE WEATHER FORECAST

Use cobalt chloride as a humidity detector to predict the possibility of rain

Suitable For

Grade 8

Difficulty

3

Time Required

 <2 Weeks

Supervision

Required

What’s it about?

The ‘humidity’ in the air can be explained as the amount of water a volume of air holds, and is expressed as a percentage. The humidity level is often seen as an indication of the likelihood of rain occurring, and this is usually measured with a ‘hygrometer’. A chemical humidity detector or ‘hygrometer’ can be made by dipping a piece of paper or cloth in a solution of cobalt chloride, as you will see in the following science experiment:

Warning: Exercise extreme caution when working with Cobalt chloride. Do not touch or inhale the solution as it can be hazardous to your health! Ask your parents or an adult to help you with this experiment.

Topics covered

Hygrometer, Humidity, Cobalt chloride, Carcinogenic

What will I need?

  • COBALT CHLORIDE
  • WHITE BLOTTING PAPER
  • WHITE WRITING PAPER
  • WHITE CLOTH
  • CLOTHESPINS
  • TEASPOON
  • MEASURING JUG

Procedure (Method)

Unfortunately, this section is only available in the e-book version of the project.

How does it work?

Unfortunately, this section is only available in the e-book version of the project.

This science experiment works because when cobalt chloride comes in contact with water molecules, it forms a hydrate. The formation of the hydrate, wherein one or more water molecules are incorporated into the anhydrous salt, forms a new crystal structure that causes the colour change from ‘blue’ to ‘pink’. This happens because the water molecules become incorporated into the newly formed crystals.

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