1. 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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3. 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+] HA  H+ + A–
NaA + 
Na+ A–

4. Buffers Why do buffers work? Le Chatelier’s 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.

5. 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

6. 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