Strong Acids

Strong acids are acids for which the equilibrium constant for dissociations is so large that we assume the molecules "fall apart" or dissociate 100% in water.

For example, HCl is a strong acid.  So for the equilibrium

\[\rm{HCl(aq) + H_2O(l) \rightleftharpoons H_3O^+(aq) + Cl^-(aq)}\]

we assume the equilibrium constant is so large (it is more than 10⁶) that the reaction will essentially go to completion.  That is when we put HCl in water, it will completely dissociate and form H₃O⁺ and Cl^-.  This is what we mean by strong.  We call it an acid because it is donating a proton (H⁺) to water.

You need to memorize the list of strong acids.  Both their names and formulas

Hydrochloric acid - HCl
Hydrobromic acid - HBr
HydroIodic acid - HI
Perchloric acid - HClO₄
Chloric acid - HClO₃
Sulfuric acid - H₂SO₄ (note only the first proton is strong)
Nitric acid - HNO₃

A video on the definitions of Strong Acids and Strong Bases. Complete or 100% dissociation is required. A video showing the 7 Strong Acids and 8 Strong Bases. Strong acids and bases are strong electrolytes which means they ionize completely (100%). All students should MEMORIZE these two sets of compounds.