- Buffer capacity: represents the amount of H+ or OH- the buffer can absorb without a significant change in pH
- The buffer capacity is determined by the [A-] & [HA] (molarity)
○ More moles = greater capacity
○ Less moles = less capacity bcuz there is less buffer to react with
How to Choose a Buffer
- The buffer is most effective (most resistant to change) when [A-] = [HA] → means that pH = pKa (since log 1 = 0)
■ To determine the pKb of a weak base, do 14 – pKa
- When choosing a buffer, choose the buffer system whose pKa is closest to the desired pH
pH of Buffer Solution After Adding Acid or Base
- Scenario 1: adding less moles of acid/base than buffer
- Subtract moles of acid/base from weak HA or base and add moles of acid/base to conjugate
- Then use Henderson-Hasselbalch
- Scenario 2: adding more moles of acid/base than buffer
- Determine how many moles of acid/base remains after reacting with buffer → use either [H+] or [OH-] to determine pH