Equivalent weight

Equivalent weight

Equivalent weight is the amount of an element that reacts, or is involved in reaction with, 1 mole of electrons. It is 'defined' by many texts as the weight of the element combining with 1 g hydrogen, 8 g oxygen or 35.5 g chlorine, each of which would either provide or accept one mole of electrons in a reaction. This concept is very useful in gravimetric and volumetric analysis.

When choosing primary standards in analytical chemistry, compounds with higher equivalent weights are generally more desirable because weighing errors are reduced or minimized.

For example, hydrogen, with atomic weight 1.008 and valence 1, has an equivalent weight of 1.008. Oxygen assumes a valence of 2 and has an atomic weight of 15.9994, so it has an equivalent weight of 7.9997.

Elements may assume different equivalent weights in different compounds. For example, iron (atomic weight 55.845) assumes equivalent weight 27.9225 if it is valence 2 in the compound (ferrous); or 18.615 if it is valence 3 (ferric).

The equivalent weight can also be computed for other than pure elements. For example, the carbonate radical (CO32-) has a formula (atomic) weight of 60.0092 and assumes valence 2 in compounds, so its equivalent weight is 30.0046.

The equivalent weight of a substance may be defined as that weight of it which will react with or produce one mole of hydrogen. (Or 1g of H since 1mol H=1g H)

Equivalent weight in Polymer Chemistry signifies the amount of reactive functional groups on the polymer chain . Its value denotes gram solid resin that includes one mole of functional reactive group attached to the polymer backbone.

It is widely used to indicate the reactivity of polyol, isocyanate, or epoxy thermoset resins which would undergo crosslinking reactions through those functional groups. The formula to calculate the equivalent weight of particular functional reactive groups is as follows;

% Functional reactive group (FRG) = (gr of FRG)/(100gr resin)*100

Equivalent Weight = (MW of FRG)/(% FRG) * 100

ex: For an acrylic polyol resin, MW of -OH=17;

% -OH = (gr of -OH)/(100gr acrylic resin)*100

Equivalent weight of -OH = 17/(%-OH)*100


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  • equivalent weight — n EQUIVALENT (1) * * * the amount of a substance that combines with or displaces 8.0 g of oxygen (or 1.008 g of hydrogen), usually expressed in grams; for acid base reactions, one equivalent donates or receives a mole of protons, and the… …   Medical dictionary

  • equivalent weight — Chem. the combining power, esp. in grams (gram equivalent), of an element or compound, equivalent to hydrogen as a standard of 1.00797 or oxygen as a standard of 8; the atomic weight divided by the valence. [1925 30] * * * or combining weight… …   Universalium

  • equivalent weight — noun 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 • Hypernyms: ↑atomic mass, ↑atomic weight, ↑relative atomic… …   Useful english dictionary

  • equivalent weight — noun 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. In the proportion d : p :: 1 : v, as a …   Wiktionary

  • equivalent weight — ekvivalentų molio masė statusas T sritis Standartizacija ir metrologija apibrėžtis Medžiagos molio masės ir ekvivalentinio daugiklio sandauga. atitikmenys: angl. equivalent weight; molar mass of equivalents rus. мольная масса эквивалентов, f;… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

  • equivalent weight — ekvivalentų molinė masė statusas T sritis chemija apibrėžtis Medžiagos molinės masės ir ekvivalentinio daugiklio sandauga. atitikmenys: angl. equivalent weight; molar mass of equivalents rus. мольная масса эквивалентов …   Chemijos terminų aiškinamasis žodynas

  • equivalent weight — equiv′alent weight′ n. chem. the combining power, esp. in grams (gram equivalent), of an element or compound, equivalent to hydrogen as a standard of 1.00797 or oxygen as a standard of 8; the atomic weight divided by the valence. • Etymology:… …   From formal English to slang

  • equivalent weight — noun Date: circa 1855 the mass of a substance especially 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 …   New Collegiate Dictionary

  • equivalent weight — /əˌkwɪvələnt ˈweɪt/ (say uh.kwivuhluhnt wayt) noun Chemistry Obsolete the weight of an element or compound which will combine with, or replace, 1.007 97 grams of hydrogen or 8 grams of oxygen; for an element, the atomic weight divided by the… …  

  • equivalent weight —    see equivalent …   Dictionary of units of measurement

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