Definition: equivalent weight from Merriam-Webster's Collegiate(R) Dictionary

(ca. 1855) : the mass of a substance esp. in grams that combines with or is chemically equivalent to eight grams of oxygen or one gram of hydrogen :the atomic or molecular weight divided by the valence

Summary Article: equivalent weight
From The Columbia Encyclopedia

The equivalent weight of an element or radical is equal to its atomic weight or formula weight divided by the valence it assumes in compounds. The unit of equivalent weight is the atomic mass unit; the amount of a substance in grams numerically equal to the equivalent weight is called a gram equivalent. Hydrogen has atomic weight 1.008 (rounded to three decimal places) and always assumes valence 1 in compounds, so its equivalent weight is 1.008. Oxygen has an atomic weight of 15.999 and always assumes valence 2 in compounds, so its equivalent weight is 7.9995. The sulfate radical (SO4) has formula weight 96.0636 and always has valence 2 in compounds, so its equivalent weight is 48.0318. Some elements exhibit more than one valence in forming compounds and thus have more than one equivalent weight. Iron (atomic weight 55.845) has an equivalent weight of 27.9225 in ferrous compounds (valence 2) and 18.615 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, 7.9995 to 1.008 or 7.936 to 1; there is 1 weight of hydrogen for every 7.936 weights of oxygen, or water is about 11.2% hydrogen (by weight). Iron forms two oxides: ferrous oxide (FeO), in which there are 27.9225 weights of iron for each 7.9995 weights of oxygen, and ferric oxide (Fe2O3), in which there are 18.615 weights of iron for every 7.9995 weights of oxygen.

The Columbia Encyclopedia, © Columbia University Press 2018

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Collins English Dictionary

n 1 the weight of an element or compound that will combine with or displace 8 grams of oxygen or 1.007 97 grams of hydrogen Also called: gram equiv

##### Full text Article equivalent weight
The Penguin Dictionary of Science

The mass of an element that can combine with or displace one gram of hydrogen. The term is obsolete, having been replaced by the concept of ➤molar m

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