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Question
Which of the following salt has a blue colour and why?
CuSO4.5H2O or CuSO4
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Solution
The CuSO4.5H2O has a blue colour. The blue colour is due to the presence of water molecules in the structure. The colour of a salt crystal is usually given by the water of crystallisation. But anhydrous salts (without the water molecules) lose their colour and shape and become white. Thus, CuSO4, which does not have water molecules, appears white.
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