Question

Which one of the following methods can be used to test the presence of water?

• A. Smell the liquid
• B. Add anhydrous copper sulphate and look for a colour change
• C. Taste the liquid
• D. Litmus paper with the solution

Answer 1

Answer: (B)

Add anhydrous copper sulphate and look for a colour change

The reaction between anhydrous copper sulfate and water is reversible:

Anhydrous copper sulfate (white) $+$ water $=$ Hydrated copper sulfate (blue)

$CuSO4+5H_{2}O\to CuS{O}_4.5H_{2}O$.

White anhydrous amorphous copper sulfate combines with $5$ molecules of water to form hydrous blue copper sulfate (blue vitriol).