citric acid has an acid dissociation constant of 8.4 x 10^-4 it would be most effective for preparation of a buffer with a pH of

Question

fredd [130]

3 years ago

12

citric acid has an acid dissociation constant of 8.4 x 10^-4 it would be most effective for preparation of a buffer with a pH of

(A) 2 (B) 3 (C) 4 (D) 5

Chemistry

1 answer:

Sloan [31] · Answer 1 · 2022-07-18T07:35:06+03:00

Answer:

(B) 3

Explanation:

Citric acid has an acid dissociation constant (Ka) of 8.4 × 10⁻⁴. When it forms a buffer with its conjugate base (citrate), we can calculate the pH using the Henderson-Hasselbalch's equation.

$pH=pKa+log\frac{[base]}{[acid]}$

The optimum range of pH is pKa ± 1. The pKa is -log Ka = -log (8.4 × 10⁻⁴) = 3.1. The buffer would be more effective for pH between 2.1 and 4.1, especially around 3.1. So the best choice is (B) 3.