Question

Acetic acid is 5% ionised in its decimolar solution. Calculate the dissociation constant of acid.

Answer 1

Given: Percent dissociation (α) = 5% = 0.05

Concentration (C) = 1 decimolar = 0.1 M

For weak acid (K_a) = `(C alpha)^2/(1 - alpha)`

= `(0.1 xx (0.05)^2)/(1 - 0.05)`

= `(0.1 xx 0.0025)/0.95`

= `0.00025/0.95`

= 2.63 × 10⁻⁴

∴ The dissociation constant of the acid is 2.63 × 10⁻⁴.