Question

Define the following terms with a suitable example in each case : \[ (i)\ \text{Ambidentate ligand} \] \[ (ii)\ \text{Double salt} \]

Hint:

Double salts lose their identity in solution and dissociate completely, whereas coordination compounds retain the identity of the complex ion in solution.

Answer 1

(i) Ambidentate Ligand

Definition: An ambidentate ligand is a ligand that contains two different donor atoms and can coordinate to the central metal atom through either one of these donor atoms, but not through both simultaneously. Thus, the ligand possesses more than one possible point of attachment.

Explanation: Depending upon which donor atom binds to the metal, different linkage isomers may be formed. Such ligands play an important role in coordination chemistry because they can give rise to linkage isomerism.

Example: Nitrite ion: \[ NO_2^- \] can coordinate through nitrogen: \[ M-NO_2 \] or through oxygen: \[ M-ONO \] Hence nitrite ion is an ambidentate ligand. Other examples include: \[ SCN^- \] and \[ CN^- \]

Final Definition: \[ \boxed{\text{An ambidentate ligand can coordinate through either of two different donor atoms.}} \] Example: \[ \boxed{NO_2^-} \]

(ii) Double Salt

Definition: A double salt is a crystalline compound formed by the combination of two or more simple salts in a definite stoichiometric ratio. When dissolved in water, a double salt completely dissociates into all the constituent ions.

Explanation: The properties of a double salt in aqueous solution are the same as those of the individual ions obtained after dissociation. Unlike coordination compounds, double salts do not retain their identity in solution.

Example: Mohr's salt: \[ FeSO_4 \cdot (NH_4)_2SO_4 \cdot 6H_2O \] On dissolution: \[ FeSO_4 \cdot (NH_4)_2SO_4 \cdot 6H_2O \rightarrow Fe^{2+}+2NH_4^+ +2SO_4^{2-} \] Thus all constituent ions are produced independently. Other examples include: \[ K_2SO_4 \cdot Al_2(SO_4)_3 \cdot 24H_2O \] (Potash alum)

Final Definition: \[ \boxed{\text{A double salt dissociates completely into all constituent ions when dissolved in water.}} \] Example: \[ \boxed{\text{Mohr's Salt}} \]