Enough of a monoprotic acid is dissolved in water to produce a 1.81 M solution. The pH of the resulting solution is 2.88 . Calculate the Ka for the acid.

Question

Enough of a monoprotic acid is dissolved in water to produce a 1.811.81 M solution. The pH of the resulting solution is 2.882.88. Calculate the K_a for the acid.

Answer 1

Let the monoprotic acid be represented as HA

HA <==> H⁺ + A^- (ionization of the acid in water)

Ka = [H+][A-] / [HA]

We can find [H⁺] and [A^-] from the given pH of 2.88 as follows:

pH = -log [H⁺]

[H⁺] = 1x10^-2.88

[H⁺] = = [A-]

Now substitute these values and the given [HA] into the Ka expression and solve for Ka:

Ka = [1.32x10^-3][1.32x10^-3] / [1.81]

Ka = 9.63x10^-7