Chemistry titration question?

2017-10-29 11:21 pm

Using 0.100 mol L–1 NaOH, a student titrated 25.0 mL of a 0.100 mol L–1 weak
monoprotic acid, and separately titrated 25.0 mL of a 0.100 mol L–1 strong
monoprotic acid.

Which statement about the volume of base required to reach the equivalence point is correct?
(A) The weak acid will require the same volume of base as the strong acid.
(B) The weak acid will require a larger volume of base than the strong acid.
(C) The weak acid will require a smaller volume of base than the strong acid.
(D) The volume of base required will depend on the molar mass of the acid used.

Which statement correctly describes the pH at each titration equivalence point?
(A) The pH of both solutions will be the same.
(B) One of the solutions will be neutral while the other will have a pH higher than 7.
(C) One of the solutions will be neutral while the other will have a pH lower than 7.
(D) One of the solutions will have a pH higher than 7 while the other will have a pH
lower than 7.

im so confused please help and explain

回答 (1)

micatkie

2017-10-29 11:36 pm

✔ 最佳答案

1.
The weak acid and the strong acid are equal in number of moles. Since 1 mole of NaOH is required to neutralize 1 mole of monoprotic acid no matter whether the acid is weak or strong, then equal numbers of moles of NaOH is required for complete neutralization in both titrations. When the same NaOH is used in titration, the same volume of NaOH solution is used in both titrations.

The answer: (A) The weak acid will require the same volume of base as the strong acid.

====
2.
NaOH is a strong base.
When NaOH and a weak acid undergo complete neutralization, the final solution is slightly basic, i.e. pH > 7. This is because the anion of the salt formed in neutralization would undergo reversible hydrolysis (reaction with water) to form OH⁻ ion.
When NaOH and a strong acid undergo complete neutralization, the final solution is neutral. This is because the cation and anion of the salt formed do not react with water.

The answer: (B) One of the solutions will be neutral while the other will have a pH higher than 7.

👍 4 👎 0