The complete ionic equation for a chemical reaction involving ions is to break each species into its component ions and show what each ion does. The net ionic equation focuses only on the ions involved in the key chemical reaction and eliminates the unimportant spectator ions. Sodium hydroxide (NaOH) is a compound made up of the sodium ion (Na+) and the hydroxide ion (OH)-. Hydrochloric acid (HCl) is a chemical made up of a proton (H+) and a chloride ion (Cl-). The molecular chemical equation is given below:
`NaOH + HCl -> NaCl + H2O`
This shows that sodium hydroxide and hydrochloric acid react to form sodium chloride (salt: NaCl) and water (H2O). Since this reaction takes place in water, the component ions are what are actually present in solution to perform the reaction. The complete ionic equation is shown below:
`Na^(+) + OH^(-) + H^(+) + Cl^(-) -> Na^(+) + Cl^(-) + H2O`
The sodium and chloride ions remain unchanged in solution so they are spectator ions. The net ionic equation removes the spectator ions and is shown below:
`H^(+) + OH^(-) -> H2O`
In other words, a proton and a hydroxide ion react to form a molecule of water.