Blue crystals of copper sulphate become white on heating. What does this change prove?
Answer and explanation
Correct answer: Water of crystallisation plays a role in colour
The governing concept is the role of water of crystallisation in the colour of hydrated salts. Blue copper sulphate crystals are CuSO₄·5H₂O. Heating removes this water and produces white anhydrous CuSO₄, so the colour change demonstrates that the associated water contributes to the blue appearance. Hence option A is correct. The salt does not become gold, and sulphate does not generally turn into a gas.
Frequently asked questions
What is the correct answer to this question?
Water of crystallisation plays a role in colour
Why is this the correct answer?
The governing concept is the role of water of crystallisation in the colour of hydrated salts. Blue copper sulphate crystals are CuSO₄·5H₂O. Heating removes this water and produces white anhydrous CuSO₄, so the colour change demonstrates that the associated water contributes to the blue appearance. Hence option A is correct. The salt does not become gold, and sulphate does not generally turn into a gas.
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.
