Chapter 2, Problem 52P

Interpretation Introduction

Interpretation:

The reason for $p{K}_a$ value of $COOH$ group in the center of the citric acid is lower than $p{K}_a$ value of acetic acid has to be explained.

Concept introduction:

Conjugate acid and base: If a base receives one proton, then the formed species is a conjugate acid whereas an acid lose one proton, then the formed species is a conjugated base.

If an acid lose one proton, then the formed species is a conjugated base. Weak base forms stronger conjugated acid.

If electronegative atoms are attached to a species, it causes inductive electron withdrawal. It stabilizes its conjugate base thus increases the strength of the acid.

Inductive electron withdrawal: An electron-withdrawing group increases the strength of an acid. As the electronegativity of the electron-withdrawing group increases, or as an electron-withdrawing atom moves closer to the acidic hydrogen, the strength of the acid increases.