The metal salt A is blue in colour. When salt A is heated strongly over a burner, then a substance B is eliminated and a white powder C is left behind. When a few drops of a liquid D are added to powder C, it becomes blue again. What could be A, B, C and D
Copper sulphate crystals (A) are blue and have the chemical formula CuSO4.5H2O. When copper sulphate crystals are heated strongly, they lose all the water of crystallisation (B) and form anhydrous copper sulphate (C), which is white.
A C B
CuSO4.5H2O → CuSO4 + 5H2O
Anhydrous copper sulphate turns blue on addition of a few drops of water (D) because it gets hydrated again.
CuSO4 + 5H2O → CuSO4.5H2O
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