Buffers and Henderson-Hasselbach Equation

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Buffers and Henderson-Hasselbach Equation
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Buffers - summary

• Solutions with buffers resist changes in pH, when
  small amounts of acid or base are added
• Buffers are important in blood, cells, resisting
  the effects of acid rain on lake ecosystems.

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• A buffer is created when a weak acid is mixed
  with a salt that contains the identical ion.
• Two equilibria contribute to the consistent H

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Buffers

• Why do buffers work?
• Le Chateliers Principle
• Very little reaction occurs to change either
  concentration
• HA dissociates very little, and adding extra A-
  to the solution will make the HA dissociate even
  less.
• A- does not react with water, and addition of HA
  makes A- react even less.

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pH Calculations for Buffers

• Henderson-Hasselbalch equation
• Merely a rearrangement of the Ka equilibrium
  expression
• pH pKa log (A- / HA) for acids
• pH pKa log (B / BH) for bases

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Henderson-Hasselbalch Equation

• Properties
• All Equilibria must be satisfied simultaneously
  in any solution at equilibrium
• For the pH to change by 1 unit, A- / HA must
  change by a factor of 10.
• If HA increases, the pH must decrease
• If A- increases, the pH must increase