Question

Crystal of substance change the colour of heating is a closed vessel but regained it after sometime when they were allowed to cool down . explain the phenomenon involved

Answer 1

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One such compound is copper sulphate.
The copper sulphate crystals contain water of crystallisation. On heating they lose water of crystallisation and the colour of the salt crystals changes from blue to white.The water lost condenses on the upper part of the closed vessel. The salt crystals regain their colour on cooling, since they absorb the lost water