Monochloroethanoic acid `(ClCH_(2)COOH)` has only one chlorine atom with-I effect while dichlorethanoic acid `(Cl_(2)CHCOOH)` has two chlorine atoms. As a result, release of proton from monochloroethanoic acid is difficult as compared to dichloroethanoic acid. Therefore, monochloroethanoic acid has `pK_(a)` value (2.87) than dichloroethanoic acid (1.26) and it is a weaker acid.
