AP Chemistry Unit 8.10 Buffer Capacity

Buffer Capacity

  • Buffer capacity: represents the amount of H+ or OH- the buffer can absorb without a significant change in pH
  • The pH of a buffered solution is determined by the ratio of [A-]/[HA]
    • Same ratio = same pH
  • The buffer capacity is determined by the [A-] & [HA]
    • More moles = greater capacity
    • Less moles = less capacity bcuz there is less buffer to react with

How to Choose a Buffer

  • The most effective buffers (most resistant to change) have a ratio of [A-]/[HA] = 1
    • Is true when [A-] = [HA] → This means that pH = pKa (since log 1 = 0)
  • When choosing a buffer for a desired pH, choose the buffer system whose pKa is closest to the desired pH
    • The log of a larger number is less negative than the log of a smaller number → higher pH
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