Why does the blue colour return when water is added to white copper sulphate?
Answer and explanation
Correct answer: Because water of crystallisation is regained
Blue hydrated copper sulphate is CuSO₄·5H₂O. On strong heating, it loses its water of crystallisation and becomes white anhydrous CuSO₄. When water is added again, the salt becomes hydrated and the characteristic blue colour returns. Therefore, option C is correct. The change is not caused by formation of common salt, a metal, or chlorine. This reversible colour change demonstrates the importance of water of crystallisation in hydrated salts.
Frequently asked questions
What is the correct answer to this question?
Because water of crystallisation is regained
Why is this the correct answer?
Blue hydrated copper sulphate is CuSO₄·5H₂O. On strong heating, it loses its water of crystallisation and becomes white anhydrous CuSO₄. When water is added again, the salt becomes hydrated and the characteristic blue colour returns. Therefore, option C is correct. The change is not caused by formation of common salt, a metal, or chlorine. This reversible colour change demonstrates the importance of water of crystallisation in hydrated salts.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Acids, Bases, and Salts.
