Acetic acid and propionic acid have K a values 1.75 × 1 0 - 5 and 1.3 × 1 0 - 5 respectively at a certain temperature. An equimolar solution of a mixture of the two acids is partially neutralised by NaOH. How is the ratio of the contents of acetate and propionate ions related to the K a values and the molarity?

Question

Acetic acid and propionic acid have K a values 1.75 × 1 0 - 5 and 1.3 × 1 0 - 5 respectively at a certain temperature. An equimolar solution of a mixture of the two acids is partially neutralised by NaOH. How is the ratio of the contents of acetate and propionate ions related to the K a values and the molarity?, α 1 - α = 1.75 1.3 × β 1 - β , whereas α and β are ionized fractions of the acids, The ratio is unrelated to the K a values, The ratio is unrelated to the molarity, The ratio is unrelated to the pH of the solution

MARKS App · Accepted Answer

In a given mixture, the ionization of two acids can be written at Let α , β be degree of ionization at same concentration. C H 3 C O O H 1 - α ⇌ C H 3 C O O - α + H + α + β C 2 H 5 C O O H 1 - β ⇌ C 2 H 5 C O O - β + H + α + β So K Acetic acid = α α + β ⋅ c 1 − α K Prepionic acid = β α + β ⋅ c 1 − β So K acetic acid K propinoic acid = α 1 − α × 1 − β β or α 1 - α = 1.75 1.3 × β 1 - β .

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