Solution to Q.24: HSAB Principle Solubility Trends

HSAB principle predicts solubility trends for silver and lithium halides in water based on acid-base interactions. Ag⁺ (soft acid) binds weakly to hard F⁻ but strongly to soft I⁻, while Li⁺ (hard acid) binds strongly to hard F⁻.

Silver Halides Analysis

Silver halides follow AgF > AgCl > AgBr > AgI solubility order. Soft Ag⁺ forms strongest lattice with soft I⁻ (least soluble AgI) and weakest with hard F⁻ (most soluble AgF), confirmed by Ksp values: AgF (205) >> AgCl (1.8×10⁻¹⁰) > AgBr (5.2×10⁻¹³) > AgI (8.3×10⁻¹⁷).

• Option (A) matches this HSAB prediction and experimental data.
• Option (C) reverses the trend, so incorrect.

Lithium Halides Analysis

Lithium halides show LiBr > LiCl > LiF solubility (LiI lower due to poor I⁻ hydration). Hard Li⁺-hard F⁻ interaction yields high lattice energy for low-solubility LiF; larger halides have weaker lattices despite lower hydration.

• Option (B) aligns with observed HSAB-influenced trend.
• Option (D) reverses it, so incorrect.

Correct Options

(A) and (B) are correct per HSAB principle and experimental data.

HSAB Principle Solubility Trend Guide

The HSAB principle solubility trend governs how silver and lithium halides dissolve in water, crucial for CSIR NET Life Sciences preparation.

HSAB Principle Basics

Hard acids (small, high charge density like Li⁺) prefer hard bases (F⁻); soft acids (large, polarizable like Ag⁺) prefer soft bases (I⁻). Strong matches yield stable, low-solubility lattices in polar water.

Silver Halides: AgF > AgCl > AgBr > AgI

Ag⁺ (soft) mismatches hard F⁻ (weak lattice, high solubility) but matches soft I⁻ (strong lattice, low solubility). Matches experimental Ksp decrease down group.

Lithium Halides: LiBr > LiCl > LiF

Li⁺ (hard)-F⁻ (hard) gives highest lattice energy (lowest solubility); hydration limits perfect HSAB prediction for LiI.

Exam Relevance

GATE 2023 XL Q.24 confirms (A) and (B) correct. Essential concept for CSIR NET Chemical Sciences and GATE Life Sciences.