Question

The separation of lanthanides in the ion-exchange method is based on:
(A) Basicity of hydroxides
(B) Size of the hydrated ions
(C) Size of the unhydrated ion
(D) The solubility of their nitrates

Answer 1

All the lanthanides look like silvery-white soft metals and in presence of air tarnish rapidly. The separation of lanthanides from other elements forms lanthanide compounds which are chemically combined with specific substances. one of the best processes which is used to separate lanthanides is the ion-exchange method.

Complete step by step solution:
Methods used for the separation of lanthanides are:
(1) ion-exchange method
(2) Solvent extraction method
(3) Paper chromatography
(4) Gas chromatography
(5) thin-layer chromatography
(6) Complex formation
Ion-exchange method: the most modern method for the separation of lanthanides is the ion-exchange method. In this method, synthetic cation resins are used. These resins contain $-S{{O}_{3}}H/-COOH$ groups; the hydrogen in these resins is replaced with lanthanide ions. The aqueous solution contains a mixture of $L{{n}^{+3}}$, which is allowed to pass down a column with cation exchange resin.
$L{{n}^{+3}}(aq)+3HR(solid)\Leftrightarrow Ln{{R}_{3}}(solid)+3{{H}^{+}}(aq)$
The separation of lanthanides in the ion-exchange method is based on compounds like low solubility nitrates, oxalates, and fluorides, etc.

The correct answer is option D.

Note: Removal of $L{{n}^{+3}}$ions fixed on the resin, the ion exchange column is leached with a complex agent in an aqueous solution like a buffer solution of ammonium citrate- citric acid (pH =4-7). Such complexing agents are called eluants or eluates or eluating agents. During this process ions of the eluating agent replace $L{{n}^{+3}}$an ion that is fixed on the resin and reacts with citrate ion to form the Ln-citrate complex.