Cocl2 is often used in hygrometers. search the internet to determine why? how does this relate to this experiment?

The answer to this question would be: Because CoCl2 will change color when humidity changes.

Cobalt chloride or CoCl2 can change its color depends on the humidity. The dry cobalt chloride will have pink color but it will changes into blue if you mix it with water. If the humidity is high, the water in the air might condense into the cobalt chloride and change its color to blue. So high humidity will cause more cobalt chloride turn into blue.