Is #HF# a strong acid in water?

1 Answer
Aug 12, 2016

Answer:

#H-F# is not a strong Bronsted acid:

#HF(aq) + H_2O rightleftharpoons H_3O^+ + F^-# #;pK_a=3.17#

Explanation:

Two factors explain the reduced acidity of #HF# in relation to the lower hydrogen halides: (i) the #H-F# bond is strong; and (ii) the resultant #F^-# is small and strongly polarizing.

Both enthalpy and entropy conspire to reduce the acidity of #H-F#. The entropy effect is probably the most significant.

It is a fact that solutions of #NaF(aq)# are slightly basic. How is this consistent with the former?