A 0.2 M aqueous solution of a weak monobasic acid HA is found to be isotonic with a 0.06 M aqueous solution of K ₃[ Fe ( CN )₆] at the same temperature. Assuming complete dissociation of the complex salt, the percentage degree of dissociation of the weak acid HA is ________.

Step-by-step solution

For the complex salt K ₃[ Fe ( CN )₆] , it dissociates completely into 3 K ^+ and 1 [ Fe ( CN )₆]³⁻ ions. The van 't Hoff factor for K ₃[ Fe ( CN )₆] is i₁ = 4 . Effective concentration of K ₃[ Fe ( CN )₆] = i₁ C₁ = 4 0.06 = 0.24 M . For the weak monobasic acid HA , the van 't Hoff factor is i₂ = 1 + , where is the degree of dissociation. Effective concentration of HA = i₂ C₂ = (1 + ) 0.2 M . Since the solutions are isotonic, their effective concentrations must be equal: 0.2(1 + ) = 0.24 1 + = 1.2 = 0.2 The percent