A 0.1 M solution of a weak monobasic acid is found to be isotonic with a 0.12 M solution of urea at the same temperature. The percentage degree of dissociation of the weak acid is:

Step-by-step solution

For isotonic solutions, their osmotic pressures are equal ( ₁ = ₂ ). = i C R T Therefore, i₁ C₁ = i₂ C₂ For urea (a non-electrolyte), the van't Hoff factor i₂ = 1 . For the weak monobasic acid, let the van't Hoff factor be i₁ . i₁ 0.1 = 1 0.12 i₁ = 1.2 For a weak monobasic acid dissociating as HA H^+ + A^- , the van't Hoff factor is related to the degree of dissociation ( ) by the formula i = 1 + . 1 + = 1.2 = 0.2 Percentage degree of dissociation = 0.2 100 = 20 % . Answer: 20 %