Question

Describe how much of a 5M solution of NaOH you would need to prepare approximately 1 L of sodium actetate buffer, pH= 4.8, from 1 L of acetic acid (10 mM). Acetic acid pK_a is 4.8.

Answer 1

Apply buffer equation

pH = pKa + log(A-/HA)

if pH goal is 4.8, and pKa = 4.8

4.8= 4.8+ log(A-/HA)

A-/HA = 10^(4.8-4.8)

A-/HA = 1

meaning that

A- = HA

therefore...

if we used

mmol of acetic acid initially = MV = 1L *10 mM = 10 mmol of acid

mmol of acetate initially = 0

after additino of

x mmol of NaOH = M*V = 5*V

mmol of acetic acid after reaction= 10 - 5*V

mmol of acetate initially = 0 + 5*V

and w eknow

5*V= 10 - 5*V

10V = 10

V = 10/10

V = 1 mL of NaOH required

so pH = 4.8