Calculate pH of 100 ml buffer solution containing 0.1 g acetic acid and 0.2 g sodium actetate.

General information:
Acetic acid ( molecular weight = 60.1 g/ mole ) has pKa value equal to 4.76 ( Ka = 1.75×10^-5) at 25 °C. Sodium acetate (molecular weight = 82.0 g/ mole) is a salt of acetic acid.

Calculation:
Firstly, molar concentrations of acetic acid and sodium acetate are calculated:

Acetic acid:
number of moles = 0.1 g/ (60.1 g/ mole) = 0.0017 mole
molar concentration = 0.0017 mole/ (0.1 liter) = 0.00017 M

Sodium acetate:
number of moles = 0.2 g/ (82.0 g/ mole) = 0.0024 mole
molar concentration = 0.0024 mole/ (0.1 liter) = 0.00024 M

Next, pH is calculated using online pH calculator or by applying the buffer equation as the following:

pH = 4.91.