In chemistry, back titration is a technique used to determine the strength of an analyte through the addition of a known molar concentration of excess reagent. Back titration is also referred to as indirect titration.
Titration is an analytical method involving two solutions or reactants: an analyte and a titrant. An analyte is of unknown concentration, while the titrant, also called the standard solution, is of known quantity. During titration, a buret is typically used to carefully add the titrant to the analyte until a neutral state is achieved. Titration determines an analyte's strength in terms of molarity, normality, molality, alkalinity, acidity or precipitatability. Some of the common types of titration methods include acid-base titration, precipitation titration, reduction-oxidation titration, complexometric titration and back titration.
A back titration is conducted when one of the solutions is highly volatile such as ammonia; a base or an acid is an insoluble salt such as calcium carbonate; a reaction is particularly slow or a direct titration entails a weak base and weak acid titration, the result of which is hard to ascertain. A back titration is normally done using a two-step procedure. The analyte, which is the volatile substance, is first allowed to react with the excess reagent. A titration is then performed on the remaining amount of the known solution to determine how much is in excess and to measure the quantity consumed by the analyte.