Asked in Acids and Bases
Which has greater buffering capacity at Ph 3.5-5 acetic acid or citric acid?
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.