Arrhenius Bases

Arrhenius Definition of a base
Arrhenius bases are compounds that donate OH- ions in water solutions. The role of water is essential in this definition. Pure solids like NaOH must be dissolved in water to act like a base. There are many different bases, but they have something in common. They all have an hydroxide ion, OH1- and a metal. This last idea makes it easier to identify bases.
Bases have a hydroxide ion combined with a metal. The examples of bases are:
LiOH, KOH, NaOH, CsOH, RbOH and H2O.
Mg(OH)2, Ca(OH)2, Ba(OH)2, Sr(OH)2
Al(OH)3, Sn(OH)2, Pb(OH)2, Fe(OH)2, Fe(OH)3
You should see a common characteristic in these bases. They all have a metal element and a hydroxide ion. The reason these substances are bases is that they dissolve in water to release hydroxide ions. The limitation on these compounds is their solubility in water. Typically all metal hydroxides are bases. The problem for these compounds is that only group 1 and 2 are very soluble in water.

magnesium hydroxide


magnesium ion

hydroxide ion





Mg 2+ (aq)


2 OH1- (aq)

The (aq) means the ion is dissolved in water. The ions are in an aqueous mixture. The water does not get balanced