A 0.1 M aqueous solution of a weak monoprotic acid is found to be isotonic with a 0.04 M aqueous solution of calcium chloride ( CaCl ₂ ) at the same temperature. Assuming complete dissociation of calcium chloride, the percentage ionization of the weak acid is ________.

Step-by-step solution

For isotonic solutions at the same temperature, ₁ = ₂ , which implies i₁ C₁ = i₂ C₂ . For calcium chloride ( CaCl ₂ ), assuming complete dissociation, the van't Hoff factor i₂ = 3 (since CaCl ₂ Ca ²⁺ + 2 Cl ⁻ ). Effective concentration of CaCl ₂ = i₂ C₂ = 3 0.04 = 0.12 M For the weak monoprotic acid ( HA ), the dissociation is HA H ⁺ + A ⁻ . The van't Hoff factor i₁ = 1 + , where is the degree of ionization. Equating the effective concentrations: (1 + ) 0.1 = 0.12 1 + = 1.2 = 0.2 Percentage ionization = 100 = 0.2 1