How many moles of sodium acetate must be added to 500 mL of 0.25 M acetic acid solution to produce a buffer with a pH of 4.94? The pK_a of acetic acid is 4.74. You can neglect the change in volume when sodium acetate dissolves in the acetic acid solution.

Question

Quizplus · Accepted Answer

To make a buffer solution, we need to use the Henderson-Hasselbalch equation:

pH = pKa + log([base]/[acid])

where pKa is the dissociation constant of the acid, [base] is the concentration of the conjugate base in the buffer solution, and [acid] is the concentration of the acid in the buffer solution.

Rearranging the equation gives:

[base]/[acid] = 10^(pH - pKa)

Substituting the given values:

[base]/0.25 = 10^(4.94 - 4.74)

[base] = 0.25 * 10^(0.20)

[base] = 0.25 * 1.5849

[base] = 0.3962 M

We need to find the amount of sodium acetate (NaC2H3O2) needed to obtain this concentration:

moles of NaC2H3O2 = volume of solution (L) * concentration (M)

moles of NaC2H3O2 = 0.500 L * 0.3962 M

moles of NaC2H3O2 = 0.198 moles

Therefore, the correct answer is (D) 0.198 moles.

How Many Moles of Sodium Acetate Must Be Added to 500