Neutralisation is the reaction between the hydrogen ions in an acid and the hydroxide ions in an alkali to produce water. The ionic equation for neutralisation is (higher tier):
H+(aq) + OH-(aq) → H2O(l)
Neutralisation is an exothermic reaction – one in which heat is given out. The maximum temperature is reached when the acid solution is completely neutralised by the alkali.
A base is a metal oxide or metal hydroxide that neutralises an acid to produce a salt and water. An alkali is a soluble base.