Q1(h). Alkali-ion selectivity of resins

Answer in brief

For a typical strong-acid cation-exchange resin in water, the usual preference is Cs⁺>Rb⁺>K⁺>Na⁺>Li⁺.

Key points

• The ions have the same charge, so hydration and access to fixed anionic sites become major differentiating factors.
• Small bare Li⁺ binds water strongly and has a large effective hydrated size.
• Towards Cs, lower hydration energy and easier approach to resin sites generally increase retention.