Question

Which of the following solution(s) would be a buffer? Select all that apply.

a. 100.0 mL of a solution that contains 0.100 M benzoic acid and 0.100 M potassium benzoate
b. 100.0 mL of a 0.100 M propanoic acid to which 50.0 mL of 0.100 M sodium hydroxide has been added
c. 100.0 mL of a 0.100 M formic acid solution
d. 100.0 mL of a solution that contains 0.100 M hydrochloric acid and 0.100 M sodium chloride
e. 100.0 mL of a 0.100 M solution of acetic acid in which 0.100 g of sodium acetate is dissolved

Answer 1

Which of the following solution(s) would be a buffer? Select all that apply.
a. 100.0 mL of a solution that contains 0.100 M benzoic acid and 0.100 M potassium benzoate
b. 100.0 mL of a 0.100 M propanoic acid to which 50.0 mL of 0.100 M sodium hydroxide has been added
c. 100.0 mL of a 0.100 M formic acid solution
d. 100.0 mL of a solution that contains 0.100 M hydrochloric acid and 0.100 M sodium chloride
e. 100.0 mL of a 0.100 M solution of acetic acid in which 0.100 g of sodium acetate is dissolved

Answer 2

As a buffer is defined as the aqueous mixture of a weak acid and its conjugate base. Or a weak base and its conjugate acid. Thus:

a, b and e would be a buffer.

The benzoic acid is a weak acid, its conjugate base is the benzoate ion that comes from potassium benzoate. Thus: a is a buffer.

Propanoic acid (weak acid) reacts with a strong base as sodium hydroxide producing its conjugate base (propanoate ion). Thus, b is a buffer.

Formic acid is a weak acid but its conjugate base, formate ion is not present in the solution. Thus, c is not a buffer.

Hydrochloric acid is a strong acid and sodium chloride a salt. Thus, d is not a buffer.

Acetic acid is a weak acid, and its conjugate base, acetate ion (That comes from sodium acetate) is present in the solution. Thus, e is a buffer.