Question

Why HF is a weaker acid than HCl in aqueous solution?

Answer 1

The HCl bond should be less polarized than the HF bond. ... You are right, F is more electronegative than Cl, and if the only factor were electronegativity, HF would be stronger than HCl. But it isn't, HF is a weak acid. There is a competing factor.

Answer 2

Because of strong affinity of fluorine for hydrogen so it strongly holds hydrogen and don't loose it very easily. As in HCl due to lesser H-Cl bond dissociation enthalpy as compared toHF, HCl is stronger acid than HF. ... Thus, HF is less soluble than HCl, meaning it is also a weaker acid.