A diprotic acid H₂A has K_a1 = 1 *10¯⁴ and K_a2 = 1 * 10¯⁸. The corresponding base A²¯ is titrated with aqueous HCl, both solutions being 0.1 mol L¯¹. Which one of the following diagrams best represents the titration curve which will be seen?

Question

Quizplus · Accepted Answer

The titration curve for a diprotic acid consists of two equivalence points. The first equivalence point is due to the reaction with the first ionizable hydrogen ion, and the second equivalence point is due to the reaction with the second ionizable hydrogen ion. The pH at the first equivalence point will be slightly higher than the pKa for the reaction with the first ionizable hydrogen ion, and the pH at the second equivalence point will be slightly higher than the pKa for the reaction with the second ionizable hydrogen ion. For this particular diprotic acid, the pKa values are far apart, so the first equivalence point will be very sharp and the second equivalence point will be somewhat broader. Therefore, the best choice is B, which shows a sharp first equivalence point and a broader second equivalence point.

A Diprotic Acid H2A Has Ka1 = 1 *10¯4 and Ka2

A Diprotic Acid H₂A Has K_a1 = 1 *10¯⁴ and K_a2