Question

CuSO4.5H2O is blue in colour because

• A. It contains water of crystallization.
• B. SO42– ions absorb red light.
• C. Cu2+ ions absorb red light.
• D. Cu2+ ions absorb all colours except red from the white light.

Answer 1

Answer: (C)

Cu2+ ions absorb red light.

Answer 2

Cu2+ ion (3d9) absorbs red light from the visible region, for the promotion of 3d electrons, the ions reflect blue light and appear blue.