A drying agent, called Drierite, contains anhydrous CaSO 4 , a white compound. I

Question

A drying agent, called Drierite, contains anhydrous CaSO4, a white compound. It is hygroscopic and picks up water. It serves as a drying agent. However, when it gets too wet, it no longer serves as a drying agent. Therefore, some anhydrous cobalt(II) chloride is mixed with the calcium sulfate. When the calcium sulfate is dry so that it can function as a drying agent, Drierite is blue. However, Drierite turns violet or red when it can no longer serve as an useful drying agent. Suggest an explanation of these color changes and explain why we can tell if Drierite in a bottle can be useful as a drying agent or not by looking at its color.

Explanation / Answer

The formula forCobal chloride complex will be:[CoCl4]2-

It remains in equilibrim with a very small amount of hexahydrate of cobalt [Co(H2O)6]2+

When the chloride of coblt chloride comes in contact with water it reacts with water, as CaS4 will no longer picks up water (saturated completely)

(blue) [CoCl4]2- --> [Co(H2O)6]2+ (pink in colour)

so due to blue and pink colour the mix colour appears violet.

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