How to Perform the Cobalt Chloride Test

Written by john brennan
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Cobalt chloride is an interesting kind of salt in that it changes colour as it absorbs moisture. Strips of cobalt chloride test paper go from blue to pink as they soak up water from their surroundings or humid air. If you have some cobalt chloride, you can use it to make test strips, then perform some simple science experiments or check for leaks in pipes. Here's how it works.

Skill level:
Moderately Easy

Things you need

  • Cobalt chloride
  • Spoon
  • Filter paper
  • 5 millilitres of water in a beaker or other container
  • Desiccator (i.e. a jar partly filled with silica gel or other desiccant)
  • Tape

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  1. 1

    Add some cobalt chloride to your 5ml of water and stir until it dissolves.

  2. 2

    Take a piece of filter paper and soak it in the solution.

  3. 3

    Remove the filter paper and place it in the desiccator, which is basically just a jar with some desiccant (a chemical that absorbs water) inside.

  4. 4

    Wait until the paper is dry which might take a few hours. It will turn blue once it's dried out.

  5. 5

    Cut the paper into smaller strips to make it simpler to use.

  6. 6

    Touch a strip of the paper to a surface you want to test. If the surface is moist, the paper will turn pink.

  7. 7

    Alternatively, tape a strip of test paper to a surface you suspect is leaking or cracked and tape another strip of test paper somewhere else in the vicinity (this second test strip will serve as a control). If the test strip taped to the suspect surface quickly turns pink while your control strip remains blue, you can confirm that moisture is present.

Tips and warnings

  • You may not necessarily need to make your own cobalt chloride paper; some science supply stores will sell you test strips you can use instead.

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