Neutralisation

Neutralisation is the reaction between an acid and an alkali. The clearest way to understand this reaction is to look at what happens to the particles in solution.

An acid provides hydrogen ions, $$\ce{H+ (aq)}$$, and an alkali provides hydroxide ions, $$\ce{OH- (aq)}$$. When these ions meet, they react to form water, $$\ce{H2O (l)}$$.

Neutralisation: The particle-level change

This ionic equation is the key change in neutralisation. It shows that the reaction happens because the hydrogen ions from the acid combine with the hydroxide ions from the alkali.

At the particle level, neutralisation can be understood as the removal of the ions responsible for acidity and alkalinity. The $$\ce{H+}$$ ions are responsible for the acidic nature of the solution, and the $$\ce{OH-}$$ ions are responsible for the alkaline nature of the solution. When they react together, they are used up and water is formed.

So, when you recognise a neutralisation reaction, the essential idea to remember is this: neutralisation is the reaction of $$\ce{H+}$$ and $$\ce{OH-}$$ to produce water.