A double replacement reaction is a type of chemical reaction where two compounds exchange components to form two new compounds. This typically occurs in aqueous solutions, where the ions of the reactants swap places. For example, when sodium chloride reacts with silver nitrate, the sodium ions and silver ions exchange partners, resulting in the formation of silver chloride and sodium nitrate. These reactions often produce a precipitate, gas, or water, which can be observed as a sign of the reaction taking place. Double replacement reactions are commonly used in various applications, including titration and water treatment, to remove unwanted substances or to analyze chemical concentrations.