# Why does a strong acid have a weak conjugate base, whereas a weak acid has a relatively strong conjugate base?

Jan 1, 2016

Because a strong acid necessarily implies a weak conjugate base, and a strong base implies a weak conjugate acid.

#### Explanation:

For strong acids, the following equilibrium lies strongly to the right:

$H A + {H}_{2} O r i g h t \le f t h a r p \infty n s {H}_{3} {O}^{+} + {A}^{-}$

This implies that the conjugate BASE of $H A$, ${A}^{-}$ does not compete strongly for the proton. For weaker acids, say hydrogen fluoride, the $H - F$ is strong so that ${F}^{-}$ is moderately basic. A solution of sodium fluoride in water would be slightly basic because the basic fluroide would abstract a proton from water to give back the parent acid:

${F}^{-} + {H}_{2} O r i g h t \le f t h a r p \infty n s H F + H {O}^{-}$

A little time and effort taken to understand these definitions and equilibria will be very useful (and I mean you should consult your text). Good luck.