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W22 Cobalt chloride paper to test for water vapour in air

In the previous experiment you have learnt that water of crystallization can be removed from red cobalt chloride
leaving blue cobalt chloride which is free of water.
Try to reverse this reaction:
* Left: Add water from a 1-ml syringe to the blue cobalt chloride drop by drop.
* Middle: Test whether the salt gets warm and the colour changes from blue to red.
* Right: Add more water to dissolve all crystals and wet pieces of white paper tissue with it.
* To make cobalt chloride paper from it dry it carefully. Blue cobalt chloride paper is useful to test the environment for water: In humid air the colour changes from blue to pink.