A 0.270 M monoprotic weak acid solution has a pH of 2.50.What is the pK_a of this acid?

Question

Quizplus · Accepted Answer

The pKa of the acid can be calculated using the given pH and the concentration of the acid. Since the pH is 2.50, the concentration of H+ ions is 10^-2.50 M. For a weak acid HA ⇌ H+ + A-, the Ka is given by [H+][A-]/[HA]. Assuming the degree of dissociation is small, [HA] ≈ initial concentration = 0.270 M, and [H+] = [A-] = 10^-2.50 M. Thus, Ka = (10^-2.50)^2 / 0.270. The pKa is -log(Ka), which when calculated gives approximately 4.43.

A 0270 M Monoprotic Weak Acid Solution Has a PH of of 2.50.What