Question

$CrC{l}_3.6H_{2}O$ exists in different isomeric forms which show different colours like violet and green. This is due to:

• A. ionisation isomerism
• B. coordination isomerism
• C. optical isomerism
• D. hydrate isomerism.

Answer 1

The correct option is D hydrate isomerism.

Water molecules are exchanged inside and outside coordination sphere. The number of water molecules is different inside and outside the coordination sphere. These are called hydrate isomers.

(i) $\left[Cr\right(H_{2}O{)}_6]C{l}_3$ has six water molecules inside the coordination sphere and zero water molecules outside the coordination sphere. It is violet in colour.

(ii) $\left[Cr\right(H_{2}O{)}_{5}Cl]C{l}_2.H_{2}O$ has five water molecules inside the coordination sphere and one water molecules outside the coordination sphere. It has a blue-green colour.
(iii) $\left[Cr\right(H_{2}O{)}_{4}C{l}_2]Cl.2H_{2}O$ has four water molecules inside the coordination sphere and two water molecules outside the coordination sphere. it has a green colour.