Question

Calculate the pH of a buffer solution containing 0.1 M CH₃COOH and 0.05 M CH₃COONa. 

Dissociation constant of CH₃COOH is 1.8 × 10^-5 at 25°C.

Answer 1

Given : [CH₃COOH] = 0.1 M, 

[CH₃COONa] = 0.05 M; 

K_a = 1.8 × 10^-5; 

pH = ? 

pK_a = -log₁₀K_a 

= -log₁₀1.8 × 10 

= -(\(\bar 5.2553\)) 

= 5 – 0.2553 

= 4.7447

pH = pK_a + log₁₀\(\frac{[CH_3COONa]}{[CH_3COOH]}\)

= 4.7447 + log₁₀\(\frac{0.05}{0.1}\)

= 4.7447 + (\(\bar 1.6990\))

= 4.7447 + (-1+0.6990)

= 4.7447 – 0.3010

= 4.4437

∴ pH = 4.4437