equivalent weight. The equivalent weight of an element or radical is equal to its atomic weight atomic weight, mean (weighted average) of the masses of all the naturally occurring isotopes of a chemical element , as contrasted with atomic mass , which is the mass of any individual isotope.
..... Click the link for more information. or formula weight formula weight, in chemistry, a quantity computed by multiplying the atomic weight (in atomic mass units) of each element in a formula by the number of atoms of that element present in the formula, and then adding all of these products together.
..... Click the link for more information. divided by the valence valence, combining capacity of an atom expressed as the number of single bonds the atom can form or the number of electrons an element gives up or accepts when reacting to form a compound.
..... Click the link for more information. it assumes in compounds. The unit of equivalent weight is the atomic mass unit atomic mass unit or amu, in chemistry and physics, unit defined as exactly 1-12 the mass of an atom of carbon-12, the isotope of carbon with six protons and six neutrons in its nucleus. One amu is equal to approximately 1.
..... Click the link for more information. ; the amount of a substance in grams numerically equal to the equivalent weight is called a gram equivalent. Hydrogen has atomic weight 1.008 and always assumes valence 1 in compounds, so its equivalent weight is 1.008. Oxygen has an atomic weight of 15.9994 and always assumes valence 2 in compounds, so its equivalent weight is 7.9997. The sulfate radical (SO₄) has formula weight 106.062 and always has valence 2 in compounds, so its equivalent weight is 53.031. Some elements exhibit more than one valence in forming compounds and thus have more than one equivalent weight. Iron (atomic weight 55.847) has an equivalent weight of 27.924 in ferrous compounds (valence 2) and 18.616 in ferric compounds (valence 3). The weight proportion in which elements or radicals combine to form compounds can be determined from their equivalent weights. For example, hydrogen can combine with oxygen to form water; the weight proportion of oxygen to hydrogen in water is the same as the proportion of their equivalent weights, 7.9997 to 1.008 or 7.946 to 1; there is 1 weight of hydrogen for every 7.946 weights of oxygen, or water is about 11.2% hydrogen (by weight). Iron forms two oxides: ferrous oxide (FeO), in which there are 27.924 weights of iron for each 7.9997 weights of oxygen, and ferric oxide (Fe₂O₃), in which there are 18.616 weights of iron for every 7.9997 weights of oxygen.

equivalent weight

or combining weight

Quantity of an element that exactly reacts with (equals the combining value of) 1 g of hydrogen, 8 g of oxygen, or a corresponding amount of any other element. An element's equivalent weight is its atomic weight divided by its valence. In general, for oxidation-reduction, including electrolysis, the equivalent weight is the weight associated with the loss or gain of 6.02 × 10²³ electrons (Avogadro's number) or 96,500 coulombs of electric charge; this is also the molecular weight divided by the number of electrons lost or gained. The equivalent weight of a substance with several valences differs depending on the number of electrons transferred in the given reaction. The number of equivalent weights of any substance dissolved in one litre of solution is called the solution's normality (N). See also stoichiometry.