Question

Find the pH of a 1.935 M aqueous solution of Melanoic acid, for which Ka = 2.3 ´ 10-4.

Answer 1

Given the molar concentration of Melanoic acid = 1.935 M

Melanoic acid is a di-basi acid

So, normal concentration of Melanoic acid

C = (1.935 × 2) N

Or, C = 3.87 N

Melanoic acid is a weak acid,

We know pH of a weak acid,

pH = 0.5 ( –log Ka – log C )

Or, pH = 0.5 [ – log (2.3 × 10^-4) – log 3.87 ]

Or, pH = 0.5 [ 3.638–0.587 ]

Or, pH = 1.52

Hence, pH of 1.935 M aqueous solution of Melanoic acid = 1.52