Blue vitriol becomes white on heating. On adding a few drops of water, the blue colour returns. What does this prove?
Answer and explanation
Correct answer: It contains water of crystallisation
The governing concept is water of crystallisation in hydrated salts. Blue vitriol is hydrated copper sulphate, CuSO4·5H2O. Heating removes its crystallisation water and produces white anhydrous CuSO4. Adding water restores the hydrated form and its blue colour. Thus option A is correct; sodium chloride, basicity, or metallic character cannot explain this reversible colour change.
Frequently asked questions
What is the correct answer to this question?
It contains water of crystallisation
Why is this the correct answer?
The governing concept is water of crystallisation in hydrated salts. Blue vitriol is hydrated copper sulphate, CuSO4·5H2O. Heating removes its crystallisation water and produces white anhydrous CuSO4. Adding water restores the hydrated form and its blue colour. Thus option A is correct; sodium chloride, basicity, or metallic character cannot explain this reversible colour change.
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.
