The Bronsted - Lowry model states that an acid is a substance that donates protons, H+.
When an acid dissolves in water it donates the H+ to H2O molecules and form H3O+.
For example: HCl (aq) + H2O (l) ----> H3O+ (aq)+ Cl - (aq)
In this case HCl is the acid because it donates its H+ to H2O fo form H3O+.
Aslso, the proton, H+ of the acid may combine with other radicals. For example:
NH3 (aq) + H2O (l) ---> NH4 + (aq) + OH -
In this case H2O is an acid in front ot NH3, because H2O donates its H+ to NH3 to form NH4+.
So, you just need the reactions where one reactant is donating H+ to the other reactant. There you will have a Bronsted-Lowry acid.
