What is "equivalent weight"

n. (context chemistry English) The atomic weight of an element or radical divided by its valence; the molecular weight of a compound divided by its combining power in a specific reaction.

n. the atomic weight of an element that has the same combining capacity as a given weight of another element; the standard is 8 for oxygen [syn: equivalent, combining weight, eq]

Equivalent weight (also known as gram equivalent) is a term which has been used in several contexts in chemistry. In its most general usage, it is the mass of one equivalent, that is the mass of a given substance which will

• combine or displace directly or indirectly with 1.008 parts by mass of hydrogen or 8 parts by mass of oxygen or 35.5 parts by mass of chlorine; or
• supply or react with one mole of hydrogen cations in an acid–base reaction; or
• supply or react with one mole of electrons (e) in a redox reaction.

Equivalent weight has the dimensions and units of mass, unlike atomic weight, which is dimensionless. Equivalent weights were originally determined by experiment, but (insofar as they are still used) are now derived from molar masses. Additionally, the equivalent weight of a compound can be calculated by dividing the molecular weight by the number of positive or negative electrical charges that result from the dissolution of the compound.