Question

$CrC{l}_3\cdot 6H_{2}O$ 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

Answer: (D)

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) $\left[Cr{\left(H_{2}O\right)}_6\right]C{l}_3$ has six water molecules inside the coordination sphere and zero water molecules outside the coordination sphere. It is violet in colour.
(ii) $\left[Cr{\left(H_{2}O\right)}_{5}Cl\right]C{l}_2.H_{2}O$ has five water molecules inside the coordination sphere and one water molecules outside the coordination sphere. It has a blue-green colour.
(iii) $\left[Cr{\left(H_{2}O\right)}_{4}C{l}_2\right]Cl.2H_{2}O$ has four water molecules inside the coordination sphere and two water molecules outside the coordination sphere. it has a green colour.