An acetic acid–sodium acetate buffer of pH 5.00 is 0.100 M in NaOAc. Calculate the pH after the addition of 10mL of 0.1 M ?

Question

NaOH to 100mL of the buffer.

Answer 1

Initial buffer composition:

pH = pKa + log [NaOAC]/[HAc]

5.00 = 4.74 + log (0.100/x)

log (0.100/x) = 0.26

x = 0.055 M HAc

Addition of 10 ml (0.01 L) of 0.1 M NaOH = 0.001 moles NaOH

HAc +  NaOH  ===>  NaOAc  +  H2O

0.055....0.001.............0.100........Initial

-0.001...-0.001..........+0.001......Change

0.054........0................0.101.....Equilibrium

pH = pKa + log (0.101/0.054)

pH = 4.74 + 0.27

pH = 5.01