A 0.100 M solution of a monoprotic weak acid has a pH of 3.00. What is the pK_a of this acid?

Question

Quizplus · Accepted Answer

The pH of the solution is 3.00, which means the concentration of H+ ions is 10^-3 M. For a 0.100 M solution of a weak acid to have a pH of 3.00, the acid must dissociate to produce 10^-3 M H+ ions. The degree of dissociation (α) can be calculated as α = [H+]/[Acid] = 10^-3 / 0.100 = 0.01. The dissociation constant (Ka) for the weak acid can be calculated using the formula Ka = α^2 * [Acid] = (0.01)^2 * 0.100 = 10^-5. The pKa is the negative logarithm of Ka, so pKa = -log(10^-5) = 5.00.

A 0100 M Solution of a Monoprotic Weak Acid Has a a PH