Question

$CuS{O}_4\cdot 5H_{2}O$ is blue is colour while $CuS{O}_4$ is colourless due to:

• A. presence of strong field ligand in $CuS{O}_4\cdot 5H_{2}O$
• B. due to absence of water (ligand), d - d transitions are not possible in $CuS{O}_4$
• C. anhydrous undergoes d - d transitions due to crystal field splitting
• D. colour is lost due to unpaired electrons.

Answer 1

The correct option is B due to absence of water (ligand), d - d transitions are not possible in $CuS{O}_4$

In $CuS{O}_4\cdot 5H_{2}O$, water acts as ligand and causes crystal filed splitting. This makes d - d transitions possible. On the other hand, in $CuS{O}_4$, due to absence of ligand crystal filed splitting is not possible. Hence no colour is observed.