Answer to Question #307778 in General Chemistry for kkk

Question

“Substance E is composed of clear, red crystals. When the red crystals are heated, they crackle and change into a blue liquid, which cools to form a blue solid. Heating also produces vapour of substance X, which condenses to form a liquid that is a non-conductor of electricity. The colourless liquid of substance X is cooled until it forms a white solid. The solid of substance X does not conduct electricity. The red crystals of substance E are found to be quite soluble in water, but they do not dissolve in kerosene. Neither the red crystals nor the blue solid conducts electricity, although the red aqueous solution of substance E is a good conductor.”

 

Answer 1

Crystals of a substance which changed their colour on heating in a closed test tube but regained it after sometime when they were allowed to cool down are copper sulphate or more specifically hydrated copper sulphate. Its formula - CuSO₄ × 5H2O. The phenomena involved is due to the presence of molecules of water of crystallization in the molecule. Water of crystallization is the fixed number of water molecules that are present in one formula unit of a salt. When we heat the crystals of hydrated copper sulphate this water is removed and the salt turns white. But when it is allowed to cool down in open air then it regains its lost water of crystallization and hence regains its colour also.