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?
A is a metal salt which is blue in colour, therefore, it is copper sulphate pentahydrate, CuSO4.5H2O
When salt A (CuSO4.5H2O) is heated strongly over a burner, then a substance B is eliminated and a white powder C is left behind, therefore B is water, H2O and C is anhydrous copper sulphate, CuSO4
When a few drops of a liquid D are added to powder C, it becomes blue again, therefore, D is water, H2O.
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