Cobalt chloride is another transition metal salt used to test for water. In fact it is the colouring agent added to silica gel for use in dessicators which I mentioned in my January 31st post.
Hydrated cobalt chloride has the formula CoCl2.6H2O and is deep purple in colour.
Cobalt chloride is also toxic. Safety precautions must be employed to avoid contact with skin or inhaling its dust. Always use gloves and a fume cupboard when dealing with cobalt chloride or silica gel impregnated with it.
So it’s the opposite of copper (II) sulfate whose hydrated form is blue, CuSO4.5H2O
With cobalt (II) chloride the dehydrated form is blue and the hydrated form is pink, [CoCl2(H2O)4].2H2O
Having covered chemical tests for water in my last two posts, what is the test for hydrogen gas in the school laboratory?