Electron releasing groups (Alkyl groups) de stabilizes conjugate base.
The $+$ I effect of $\mathrm{C}_3 \mathrm{H}_7$ is less than $-1$ effect of $\mathrm{Cl}$
$\mathrm{K}_{\mathrm{a}}$ of $\mathrm{HCOOH}$ is $17.9 \times 10^{-5}$
$\mathrm{K}_{\mathrm{a}}$ of $\mathrm{CH}_3 \mathrm{CH}_2 \underset{\mathrm{Cl}}{\mathrm{CH}}-\mathrm{COOH}$ is $139 \times 10^{-5}$