How many moles of sodium acetate NaOCOCH₃ must be added to 420 mL of 0.300 M acetic acid solution to produce a buffer with a pH of 5.00?

Data: pKa (CH₃COOH/CH₃COO^-) = 4.74

Question

How many moles of sodium acetate NaOCOCH₃ must be added to 420 mL of 0.300 M acetic acid solution to produce a buffer with a pH of 5.00?

Data: pKa (CH₃COOH/CH₃COO^-) = 4.74

| General Chemistry 3

Accepted Answer

Henderson-Hasselbalch equation can be used:

pH = pKa + log $\frac{{[base]}_{0}}{{[acid]}_{0}}$

log

\frac{{[base]}_{0}}{{[acid]}_{0}}

= pH – pKa

\frac{{[base]}_{0}}{{[acid]}_{0}}

= 10^{pH – pKa}

n_base = V x [acid]₀ x 10^{pH – pKa}

n_base = 0.420 x 0.300 x 10^0.26

n_base = 0.229 moles

Exercise 2 | Buffers and Acid-Base Titrations