Henderson–Hasselbalch: buffer pH from a ratio
A buffer contains acetic acid (pKa = 4.76) and sodium acetate with [acetate]/[acetic acid] = 10. What is the pH of the solution?
Answer C: explanation for every choice
A
This uses the inverted ratio, [HA]/[A⁻], in the Henderson–Hasselbalch equation.
B
pH = pKa only when [A⁻] = [HA].
C
Correct. pH = pKa + log([A⁻]/[HA]) = 4.76 + log 10 = 5.76.
D
This corresponds to a ratio of 100 (log 100 = 2).
TakeawayEach 10-fold change in the base:acid ratio shifts pH by 1 unit.
Equation usedHenderson–Hasselbalch
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