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pH and Solubility

The solubility of many ionic compounds is affected by the pH of the solution, especially salts containing weak acids or bases.

Key Concepts​

  • Acidic solutions increase solubility of salts containing anions of weak acids
  • Basic solutions increase solubility of salts containing cations of weak bases
  • Solubility changes because [H⁺] or [OH⁻] shifts the equilibrium of dissolution

Example​

  • For CaCO₃(s) ⇌ Ca²⁺(aq) + CO₃²⁻(aq):
    • Adding H⁺ → CO₃²⁻ reacts → shifts equilibrium → more CaCO₃ dissolves
  • For NH₄OH(s) ⇌ NH₄⁺(aq) + OH⁻(aq):
    • Increasing OH⁻ → shifts equilibrium → less NH₄OH dissolves

Importance​

  • Predicts solubility under different pH conditions
  • Essential for precipitation reactions and titrations
  • Used in analytical chemistry and environmental applications

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