# Is HF a strong acid or weak?

Mar 31, 2017

$\text{Hydrogen fluoride is a weak acid in water............}$

#### Explanation:

We interrogate the equilibrium:

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

${K}_{a} = \frac{\left[{H}_{3} {O}^{+}\right] \left[{F}^{-}\right]}{\left[H F\right]} = 6.3 \times {10}^{-} 4$;

Since the equilibrium lies strongly to the left, we would classify $H F$ as a weak acid. Salts of $\text{hydrogen fluoride}$ i.e. $N a F$ or $K F$ give slightly BASIC solutions in water. Why should this be so?