▁additional ▁such ▁salt ▁precip it ates ▁out ▁of ▁the ▁solution . ▁ ▁For ▁a ▁subst ance ▁to ▁be ▁class ified ▁as ▁an ▁Arr hen ius ▁base , ▁it ▁must ▁produce ▁hydro x ide ▁ ions ▁in ▁an ▁a que ous ▁solution . ▁Arr hen ius ▁believed ▁that ▁in ▁order ▁to ▁do ▁so , ▁the ▁base ▁must ▁contain ▁hydro x ide ▁in ▁the ▁formula . ▁This ▁makes ▁the ▁Arr hen ius ▁model ▁limited , ▁as ▁it ▁cannot ▁explain ▁the ▁basic ▁properties ▁of ▁a que ous ▁solutions ▁of ▁am mon ia ▁( N H 3 ) ▁or ▁its ▁organ ic ▁derivatives ▁( am ines ). ▁There ▁are ▁also ▁bases ▁that ▁do ▁not ▁contain ▁a ▁hydro x ide ▁ion ▁but ▁never theless ▁react ▁with ▁water , ▁resulting ▁in ▁an ▁increase ▁in ▁the ▁concentration ▁of ▁the ▁hydro x ide ▁ion . ▁An ▁example ▁of ▁this ▁is ▁the ▁reaction ▁between ▁am mon ia ▁and ▁water ▁to ▁produce ▁am mon ium ▁and ▁hydro x ide . ▁In ▁this ▁reaction ▁am mon ia ▁is ▁the ▁base ▁because ▁it ▁accepts ▁a ▁pro ton ▁from ▁the ▁water ▁mole c ule . ▁Am mon ia ▁and ▁other ▁bases ▁similar ▁to ▁it ▁usually ▁have ▁the ▁ability ▁to ▁form ▁a ▁bond ▁with ▁a ▁pro ton ▁due ▁to ▁the ▁un shared ▁pair ▁of ▁electrons ▁that ▁they ▁possess . ▁In ▁the ▁more ▁general ▁Br ø n sted – L ow ry ▁acid – base ▁theory , ▁a ▁base ▁is ▁a ▁subst ance ▁that ▁can ▁accept ▁hydro gen ▁c ations ▁( H +) — other wise ▁known ▁as