When a 0.089M aqueous solution of a certain acid is prepared, the acid is 12.% dissociated. Calculate the pH of the solution. Round your answer to 2 decimal places.

pH = 1.98

Explanation:

Given a general acid dissociation:

HA + H₂O ⇆ H₃O⁺ + A⁻

The pH is - log[ H₃O⁺ ]

Therefore we need to determine [ H₃O⁺ ] to answer this question, and we should use the data of % dissociation of the acid.

Percent dissociation is

% dissociation = [ H₃O⁺ ] / [ HA ]₀ x 100

where [ HA ]₀ is the original acid concentration, so we can calculate [ H₃O⁺ ], and then the pH.

12 = [ H₃O⁺ ] / 0.089 M ⇒ [ H₃O⁺ ] = (12 x 0.089 / 100) M

= 1.07 x 10⁻² M

and pH = - log (1.07 x 10⁻²) = 1.98