# What are strong Bronsted acids?

These are acids for which the following equilibrium lies strongly to the right: $H A + {H}_{2} O r i g h t \le f t h a r p \infty n s {H}_{3} {O}^{+} + {A}^{-}$
Examples of strong Bronsted acids include $H C l$, $H B r$, $H I$, ${H}_{2} S {O}_{4}$, and $H C l {O}_{4}$. Solutions of these acids are stoichiometric in ${H}_{3} {O}^{+}$ and ${X}^{-}$.
Of course, when we write the acidium species in water, ${H}_{3} {O}^{+}$, this is more of a conceptual representation than the reality. ${H}_{3} {O}^{+}$ in water is probably a cluster of 4-5 water molecules with an extra proton associated to give, say ${H}_{9} {O}_{4}^{+}$. If we treat acid as ${H}_{3} {O}^{+}$ or even as ${H}^{+}$, we are nevertheless able to do calculations and measurements successfully.