Citric acid is a triprotic acid with three carboxylic acid groups having pK_a values of 3.1, 4.8, and 6.4. If a solution of citric acid has a pH of 5.5, what can be said about the predominant protonation state of the citric acid? A)1 carboxylic acid group is deprotonated, 2 are protonated B)2 carboxylic acid groups are deprotonated, 1 is protonated C)all 3 carboxylic acid groups are deprotonated D)all 3 carboxylic acid groups are protonated E)the protonation state cannot be determined

Question

Quizplus · Accepted Answer

The pH of the solution is 5.5, which is between the second and third pKa values of citric acid (4.8 and 6.4). This means that two of the carboxylic acid groups are likely deprotonated (since the pH is above their pKa values), and one remains protonated (since the pH is below its pKa value).

Citric Acid Is a Triprotic Acid with Three Carboxylic Acid