Which property of hydrogen fluoride causes it to be a weak acid in an aqueous solution?

1 Answer
anor277
Jul 1, 2016

#(i)# strength of the #H-F# bond, and #(ii)# charge density of the fluoride ion.

Explanation:

#H-X + H_2O rightleftharpoons H_3O^(+) + X^-#

The hydrogen fluoride bond is definitely stronger than the #H-Cl# or #H-Br# bond; and thus enthalpy disfavours the forward reaction. More importantly, the #F^-# ion is smaller and more polarizing than #Cl^-# or #Br^-#. #F^-# is thus disfavoured by entropy, in that it causes more solvent order.

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