Question

The structure of haloacetic acids, XCH2COOH (where X is either F, Cl, Br, or I), is shown above. The dissociation constants and molar masses of four haloacetic acids are listed in the table below.

A student titrates 10.0 mL samples of 1.0 M solutions of each of the haloacetic acids with a standard solution of NaOH. Which of the following statements correctly predicts the volume of NaOH(aq) needed to reach the equivalence point?

a) Fluoroacetic acid will need the smallest volume of NaOH(aq) to reach the equivalence point.
b) Iodoacetic acid will need the smallest volume of NaOH(aq) to reach the equivalence point.
c) All of the acids will need the same volume of NaOH(aq) to reach the equivalence point.
d) All of the haloacetic acids are weak; therefore, none will reach an equivalence point.

Answer 1

All haloacetic acids will need the same volume of NaOH(aq) to reach the equivalence point, as they are all monoprotic and start with the same molarity and volume.

Step-by-step explanation:

The student's question concerns the volume of NaOH(aq) necessary to reach the equivalence point during a titration of various haloacetic acids, each with a different halogen atom (F, Cl, Br, or I). The correct answer is that all of the haloacetic acids will need the same volume of NaOH(aq) to reach the equivalence point, which corresponds to the point during the titration when the molar amount of NaOH added equals the molar amount of haloacetic acid originally present. This is because all the acids are starting at the same molarity and volume, and each is monoprotic, releasing one H+ ion per molecule of acid. Additionally, the fact that they are all weak acids does not affect the volume of NaOH needed to reach the equivalence point; it only affects the pH at the equivalence point.