• 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

  1. 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
  1. 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