Question

Acetic acid is weaker than chloroacetic acid. Give reason.

Answer 1

The chlorine atom, which is an electron withdrawing group is present in the alpha position of the carboxyl group, it withdraws electrons from the carbon of the carboxyl acid as well as from the oxygen of the O-H bond. This decreases electron density of the O-H bond. Consequently, the O-H bond gets weakened and the release of $H^{+}$ ion is favored.
Once the proton is released, the negative charge present on the carboxylate ion gets dispersed by the same inductive effect (-I) of the halogen atom which has a positive effect on its stability.
The same effect can be enhanced in molecules such as trifluoroacetic acid $\left(C{F}_{3}COOH\right)$ which has a pKa of 0.2 or $C{F}_{3}S{O}_{2}OH$. The latter is a so-called super acid and is 1000 times more acidic than sulphuric acid.