gramequivalent

Gramequivalent, often written as gram-equivalent, is a classical chemistry concept used to express the reactive capacity of a substance in a chemical reaction. A gram-equivalent of a substance is the amount that will react with or supply one mole of a given reactive unit, such as one mole of hydrogen ions or one mole of electrons, in a specified reaction.

The gram equivalent weight (EW) is the mass, in grams, that corresponds to one equivalent. It is calculated as the molar mass (M) divided by the substance’s reactive valence (n): EW = M / n. The value of n depends on the reaction context: for acid-base reactions it is related to the number of replaceable hydrogens or basic equivalents, and for redox reactions it relates to the number of electrons transferred per formula unit. The gram equivalent mass thus represents the amount of substance needed to supply one equivalent of reactive capacity.

Equivalents provide a link between mass and chemical reactivity. The number of equivalents in a mass m is given by equivalents = m / EW. In practice, older laboratory work frequently used equivalents or normality (equivalents per liter) in titration calculations. Modern practice often emphasizes moles and molarity, but the concept of equivalents remains useful for understanding reactionsto stoichiometry, acid-base behavior, and redox processes.

See also: Normality, molar mass, valence, acid-base theory, redox chemistry.