An acid-base reaction involves the transfer of protons (H⁺ ions) between substances. Acids are substances that donate protons, while bases accept them. This interaction can change the properties of the substances involved, often resulting in the formation of water and a salt. Common examples include the reaction of hydrochloric acid (HCl) with sodium hydroxide (NaOH), which produces water and sodium chloride (NaCl). The strength of an acid or base is measured by its pH level, which ranges from 0 to 14. A pH less than 7 indicates an acid, while a pH greater than 7 indicates a base. A pH of 7 is considered neutral, as seen in pure water. Understanding acid-base chemistry is essential in various fields, including biology, chemistry, and environmental science.