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Acids and Bases

Which has greater buffering capacity at Ph 3.5-5 acetic acid or citric acid?

Answer

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June 26, 2007 11:55PM

The ideal buffer has a pKa equal to the pH of the solution (see the Related Questions links for more about this).

Citric acid is a triprotic acid (C(OH)(CH2CO2H)2CO2H), and therefore has 3 different pKa's (for each acid group): 3.13, 4.76, 6.40

Acetic acid, CH3COOH is a monoprotic acid, and only has one pKa: 4.75.

Because of the multiple pKa's that span the pH range of interest (3.5-5), citric acid would have a high buffering capacity than acetic acid for the same concentration of buffer solution.