"Cobalt colors" experiment
How to make a cobalt indicator
Have you ever wondered how employers at service centers can tell that your smartphone has got wet? Our colorful experiment will answer your question.
Dissolve 10 g of cobalt chloride (II) in 100 ml of water. Pour the obtained solution into two glasses. Pour distilled water into one glass, and concentrated hydrochloric acid into the second – the color of the solution will change to bluish-purple. If you add water to the bluish-purple solution, it will become pink again, while if you add concentrated hydrochloric acid to the second solution, it will become bluish-purple.
The cobalt chloride changes color because the salt in the solution dissociates into ions. Cobalt ions are hydrated in the solution and have a pink color. Adding concentrated hydrochloric acid to the solution changes the color of the solution to bluish-purple. This is because the chlorine ions force the water out of the water complex of cobalt.
[Co(H₂O)₆]²⁺ +4Cl⁻ ↔ [CoCl4]²⁻ + 6H₂O₅
When carrying out the experiment, wear gloves and protective glasses. The cobalt solution is carcinogenic — in the case of contact with skin, wash it away with water.
Warning! Substances of this experiment are toxic and highly dangerous for your health. Do not try this at home. Only under professional supervision.