# What is the difference between weak acids and strong acids?

Jan 24, 2016

Weak acids don't fully dissociate in the solvent, whereas strong acid do.

#### Explanation:

A strong acid, like $\text{HCl}$, ${\text{HNO}}_{3}$ or the first proton of ${\text{H"_2"SO}}_{4}$ (in water) will be almost completely liberated. In the equilibrium there'll be protons and the anion.

Weak acids, like $\text{CH"_3"COOH}$ or ${\text{H"_3"PO}}_{4}$ or ${\text{HSO}}_{4}^{-}$will "hesitate" a bit, they'll release the proton but take it back. You can say that at the equilibrium, there'll be protons, the anion and some of the acid intact.

The strenght of an acid is dictated by its ${K}_{\text{a}}$, or its $\text{p"K_"a}$, the bigger a ${K}_{\text{a}}$ is, the stronger the acid, and since the $\text{p"K_"a}$ is $- \log \left({K}_{\text{a}}\right)$, the smaller the $\text{p"K_"a}$ the stronger the acid.

The seven strong acids are:

Hydrochloric acid: $\text{HCl}$
Hydrobromic acid: $\text{HBr}$
Hydroiodic acid: $\text{HI}$
Nitric acid: ${\text{HNO}}_{3}$
Sulfuric acid: ${\text{H"_2"SO}}_{4}$
Perchloric acid: ${\text{HClO}}_{4}$
Chloric acid: ${\text{HClO}}_{3}$