EQUIVALENT WEIGHT

"A characteristic weight of a substance relating to a specific reaction the substance participates. In electrochemical reactions, the molecular weight or atomic weight divided by the number of electrons transferred during the reaction. Consequently, the equivalent weight of a substance can be different for different reactions. E.g. the equivalent weight of the cuprous ion (singly charged copper ion) is equal to its atomic weight, independently whether it is oxidized to cupric ion (doubly charged copper ion) or it is reduced to (electrically neutral) copper metal. On the other hand, the equivalent weight of the cupric ion is one half of its atomic weight if it is reduced to copper metal, but it is the atomic weight if it is reduced only to cuprous ion. "