# How do you distinguish strong acids and weak acids?

Apr 28, 2017

The strength of an acid in water depends on the extent of the following equilibrium............

#### Explanation:

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

For weak acids, e.g. $H O A c$, ${H}_{2} S {O}_{3}$, $H F$, the equilibrium lies to the left............

And for strong acids, ${H}_{2} S {O}_{4}$, $H C l {O}_{4}$, $H X \left(X \ne F\right)$, $H N {O}_{3}$ the equilibrium lies to the right, such that at equilibrium $\left[H X\right]$ is close to zero, and the aqueous solution is stoichiometric in ${H}_{3} {O}^{+}$. When you use these in calculations, these have $p {K}_{a}$ values that are $< 2 - 3$, and ionization may be regarded as complete (even for the diacid).

Because this is an experimental phenomenon, some of these $\text{strong and weak acids}$ have to be committed to memory. The practical component of your course will help you remember.