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

Question

Quizplus · Accepted Answer

The pH of 3.00 indicates that the concentration of H+ ions is 0.001 M. For a monoprotic weak acid HA, the dissociation is HA ⇌ H+ + A-. The concentration of HA initially is 0.100 M, and at equilibrium, it is approximately 0.099 M. The equilibrium expression is Ka = [H+][A-]/[HA]. Substituting the values, Ka = (0.001)(0.001)/(0.099) ≈ 1.0 x 10^-5. Therefore, pKa = -log(Ka) ≈ 5.00.

A 0100 M Monoprotic Weak Acid Solution Has a PH of of 3.00.What