When an acid and a base react, they form a salt and water. This reaction is known as neutralization. The salt is a compound that contains the positively charged ions from the base and the negatively charged ions from the acid. The water is formed from the hydrogen ions from the acid and the hydroxide ions from the base.

For example, when hydrochloric acid (HCl) and sodium hydroxide (NaOH) react, they form sodium chloride (NaCl) and water (H2O).

HCl + NaOH → NaCl + H2O