Question

Be sure to answer all parts. Calculate the pH of the following two buffer solutions: (a) 1.4 M CH3COONa/1.6 M CH3COOH. (b) 0.1 M CH3COONa/0.2 M CH3COOH.
Which is the more effective buffer? A. 1.4 M CH3COONa/1.6 M CH3COOH B. 0.1 M CH3COONa/0.2 M CH3COOH

Answer 1

Answer:

a) pH = 4.68 (more effective)

b) pH =4.44.

Explanation:

The pH of buffer solution is obtained by Henderson Hassalbalch's equation.

The equation is:

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

a) pKa of acetic acid = 4.74

[salt] = [CH₃COONa] = 1.4 M

[acid] = [CH₃COOH] = 1.6 M

$pH = 4.74 + log \frac{1.4}{1.6}= 4.68$

This is more effective as there is very less difference in the concentration of salt and acid.

b) pKa of acetic acid = 4.74

[salt] = [CH₃COONa] = 0.1 M

[acid] = [CH₃COOH] = 0.2 M

$pH = 4.74 + log \frac{0.1}{0.2}= 4.44$