The graphs labeled (a) and (b) show the titration curves for two equal-volume samples of monoprotic acids, one weak and one strong. Both titrations were carried out with the same concentration of strong base.
(i) What is the approximate pH at the equivalence point of each curve?

Key Concepts

Titration Curves

Titration curves graphically represent the change in pH of a solution as a titrant is added. In the case of monoprotic acids, the curve typically shows a gradual increase in pH until the equivalence point, where the amount of titrant added is stoichiometrically equivalent to the amount of acid present. The shape of the curve differs between strong and weak acids, with weak acids exhibiting a more gradual slope and a less pronounced jump in pH at the equivalence point.

Equivalence Point

The equivalence point in a titration is the stage at which the amount of titrant added is exactly enough to completely neutralize the analyte solution. For strong acids titrated with strong bases, the pH at the equivalence point is typically around 7, as the resulting solution contains only neutral water and salt. In contrast, for weak acids, the pH at the equivalence point is higher than 7 due to the formation of a weak conjugate base that partially hydrolyzes in solution.

Strong vs. Weak Acids

Strong acids completely dissociate in water, releasing all their protons (H+), which results in a higher concentration of H+ ions and a lower pH. Weak acids, on the other hand, only partially dissociate, leading to a lower concentration of H+ ions and a higher pH. This fundamental difference affects the shape of the titration curve and the pH at the equivalence point, with weak acids resulting in a more basic solution at equivalence compared to strong acids.