Question

An acetic acid buffer solution is required to have a pH of 5.27. You have a solution that contains 0.01 mol of acetic acid. What molarity of sodium acetate will you need to add to the solution? The pKa of acetic acid is 4.74. Show all calculations in your answer.

In this experiment, you will make an acetic acid buffer by adding sodium hydroxide (NaOH) to commercial vinegar. Commercial vinegar is usually comprised of 5% acetic acid by volume. The sodium hydroxide will react with the acetic acid to form sodium acetate (CH₃COONa). See equation below.
CH₃COOH(aq) + NaOH(aq) ---> CH₃COONa(aq) + H2O(l)

Answer 1

0.034 M

Step-by-step explanation:

In a buffer, a weak acid (or base) is in equilibrium with its conjugate base (or acid), and, because of that, the pH of the solution remains almost unaltered by the addition of an acid or base.

The pH of a buffer can be calculated by the Handerson-Halsebach equation:

pH = pKa + log[A⁻]/[HA]

Where pKa = -logKa, Ka is the equilibrium constant of the acid, [A⁻] is the concentration of the conjugate base, and [HA] is the concentration of the acid. The acid, in this case, is the acetic acid, and the conjugate base is the acetate, which comes from the sodium acetate, and they must have the same molarity (concentration).

Let's suppose a 1.00 L solution, so [HA] = 0.01

5.27 = 4.74 + log[A⁻]/0.01

log[A⁻]/0.01 = 0.53

[A⁻]/0.01 = 3.3884

[A⁻] = 0.034 M