Titration curves Knowledge-Based Practice

Questions

1. 1.

   When comparing the titration curves of several weak monoprotic acids of identical concentration titrated with the same standardized strong base, which change is observed as the acid dissociation constant ($K_a$) of the acid decreases?

   • A) The initial pH of the acid solution decreases significantly.
   • B) The pH at the equivalence point decreases closer to 7.
   • C) The vertical inflection (pH jump) around the equivalence point becomes shorter.
   • D) A larger volume of strong base is required to reach the equivalence point.
2. 2.

   During the titration of a diprotic acid, $\text{H}_2\text{A}$, with a standardized solution of sodium hydroxide, two distinct inflections corresponding to two equivalence points are observed. What is the relationship between the volume of titrant required to reach the first equivalence point ($V_1$) and the total volume required to reach the second equivalence point ($V_2$)?

   • A) $V_2 = \frac{1}{2}V_1$ because the second dissociation produces fewer hydronium ions in solution.
   • B) $V_2 = V_1 + \text{p}K_{a2}$ because the second equivalence point depends additively on the acid dissociation constant.
   • C) $V_2 = 2V_1$ because each successive stage of deprotonation consumes an equal stoichiometric amount of base.
   • D) $V_2 = 4V_1$ because the second dissociation step requires twice the concentration of hydroxide ions to shift equilibrium.
3. 3.

   When a 0.10 M solution of a strong monoprotic acid is titrated with a 0.10 M solution of a strong base at 25 °C, which statement correctly describes the resulting titration curve?

   • A) A pronounced buffer region is established halfway to the equivalence point where pH equals $\text{p}K_{\text{a}}$.
   • B) The equivalence point occurs at pH 7.00, and the curve displays a steep, wide vertical inflection region around this point.
   • C) The equivalence point occurs at a pH greater than 7.00 due to hydrolysis of the conjugate base.
   • D) The initial pH is significantly higher than that of an equimolar weak monoprotic acid solution.
4. 4.

   In the aqueous titration of a weak base with a standardized strong acid at 25 °C, which statement correctly describes the solution at the equivalence point of the titration curve?

   • A) The pH is exactly 7.00 because stoichiometric equivalence requires equal concentrations of hydronium and hydroxide ions.
   • B) The pH is greater than 7.00 because the conjugate base of the strong acid dominates the solution equilibrium.
   • C) The concentration of the unreacted weak base equals the concentration of its conjugate acid.
   • D) The pH is less than 7.00 because the conjugate acid formed undergoes hydrolysis to produce hydronium ions.
5. 5.

   During the titration of a weak monoprotic acid with a standardized strong base, which condition is satisfied at the half-equivalence point of the titration curve?

   • A) The pH of the solution is equal to 7.00.
   • B) The hydronium ion concentration equals the initial concentration of the weak acid.
   • C) All of the weak acid has been converted into its conjugate base, yielding an equivalence point.
   • D) The concentration of the unreacted weak acid equals the concentration of its conjugate base, resulting in $\text{pH} = \text{p}K_{\text{a}}$.

Answers and step-by-step solutions appear after you finish the test.