Warning: Cobalt(II) chloride is toxic and potentially carcinogenic. Do not eat or drink. Do not dump cobalt chloride down the drain. Place it in the garbage if you have a very small amount.
You will need:
Sodium chloride or potassium chloride
Dissolve the cobalt(II) chloride in water. It will make a rose-red solution. Add your chloride. You probably will not see any change. Heat it. You will see it turn blue. This is evidence for excess chloride ions. When it cools, it will turn back to rose again.
This is caused by a principle known as Le Chatalier's principle. This reaction is driven by heat: Co(H2O)6(2+) + 4 Cl(-) <=> CoCl4(2-) + 6 H2O It moves to the right when heated and to the left when cooled.