why Ka of chloroacetic acid is larger than Ka of acetic acid?

Answer 1

thina,

Gervald is right. Cl is a very electronegative atom, and that means it is pulling electron density away from the C atom, and consequently, away from the O atom. The result is that the O atom in chloroacetic acid has a slightly more positive charge than the O atom in acetic acid, and therefore the H+ ion in chloroacetic acid can more easliy dissociate from the rest of the molecule.

Answer 2

The Cl atom (highly electronegative) is pulling electron density out of the O-H bond, making it weaker and easier for the H+ to ionise.