Citric acid is a triprotic acid with three carboxylic acid groups having p K a v

Question

Citric acid is a triprotic acid with three carboxylic acid groups having pKa 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? (assume no partial charges, only +/- whole number integers)

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

Explanation / Answer

answer : B) 2 carboxylic acid groups are deprotonated, 1 is protonated

reason :

at pH =3.1 one group acid group is deprotonated

at pH = 4.8 another group is deprotonated

at pH = 6.4 last group is deprotonated. but at pH = 5.5 still one proton is present .

so two hydrogens are removed and still left one hydrogen

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