Core Reactions: Acid-base
Slide 10 of 42
Base
For now, bases are hydroxides of metals. Later we will refine this definition further.
Some of the hydroxides dissolve in water (called alkalis) to produce hydroxides ion, while others are insoluble but react with acids to produce salt and water.
The term anhydride also applies to bases. All oxides of metals are referred to as  base anhydrides.
Just as many acid anhydrides undergo hydration to produce their corresponding acid, group IA oxides, and only these, undergo hydration to produce their corresponding base.
–M2O (s) + H2O (l) ® 2MOH (aq) 
Where, M = group IA metal. For example:
–Na2O (s) + H2O (l) ® 2NaOH (aq)
–K2O (s) + H2O (l) ® 2KOH (aq)