# Is HF a strong acid in water?

Aug 12, 2016

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

$H F \left(a q\right) + {H}_{2} O r i g h t \le f t h a r p \infty n s {H}_{3} {O}^{+} + {F}^{-}$ ;pK_a=3.17

#### Explanation:

Two factors explain the reduced acidity of $H F$ 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 $N a F \left(a q\right)$ are slightly basic. How is this consistent with the former?