Henderson-Hasselbach Equation

Introduced to this in AP Chemistry

K = = [H]

Negative log both sides

-log K = -log[H]-log

Final Equation §

pH = pK + log

pK = -logK

pK = - logK

Trends §

[HA] = [A]

• log 1 = 0
• pH = pK
• makes the best buffer solution

[HA] > [A]

• log of a # < 1 = negative
• pH < pK
• more acid than base = lower pH

[HA] < [A]

• log of a # > 1 = positive
• pH > pK
• more conjugate base than acid = higher pH

Buffering Capacity §

pH = pK + log

• pH of a buffered solution is determined by the K and the ratio
• Capacity of a buffered solution is determined by the magnitude of both [A] and [HA]
  • greater concentration of [A] and [HA] = greater amount of strong acid/base can be added with minimal pH change