Question

$CrCl_{3} \cdot 6H_{2}O$ 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)

hydrate isomerism

Answer 2

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) $\left[ Cr \left( H _{2} O \right)_{6}\right] Cl _{3}$ has six water molecules inside the coordination sphere and zero water molecules outside the coordination sphere. It is violet in colour. (ii) $\left[ Cr \left( H _{2} O \right)_{5} Cl \right] Cl _{2} . H _{2} O$ has five water molecules inside the coordination sphere and one water molecules outside the coordination sphere. It has a blue-green colour. (iii) $\left[ Cr \left( H _{2} O \right)_{4} Cl _{2}\right] Cl .2 H _{2} O$ has four water molecules inside the coordination sphere and two water molecules outside the coordination sphere. it has a green colour.