In a previous post an approximate equation to calculate buffer capacity of an acetate buffer is introduced. However, the following is an equation that can be used for exact calculations:
Where, β is the buffer capacity, C is the total buffer concentration, Ka is the acidity constant. Total buffer concentration is the sun of the concentrations of buffer components (acid and salt) in molarity. For a buffer composed from acetic acid and sodium acetate the total buffer concentration, C = [acetic acid] + [sodium acetate].
Example 1. Calculate buffer capacity of a solution composed from 0.2 M acetic acid ( Ka=
1.75 × 10-5) and 0.2 M sodium acetate at pH = 4.76.
Answer:
Example 2. Calculate the buffer capacity of the above solution after it is neutralized with KOH to pH = 7, assuming no significant change in volume after neutralization.
Answer:
It can be seen from examples 1 and 2 that the buffer capacity decreased as the difference between pH and pKa increased.
Example 1. Calculate buffer capacity of a solution composed from 0.2 M acetic acid ( Ka=
1.75 × 10-5) and 0.2 M sodium acetate at pH = 4.76.
Answer:
Example 2. Calculate the buffer capacity of the above solution after it is neutralized with KOH to pH = 7, assuming no significant change in volume after neutralization.
Answer:
