Gram equivalent

Gram equivalent

In chemistry, a gram equivalent is the mass, in grams, of a compound's equivalent weight.

More formally, a gram equivalent of a substance taking part in a given reaction is the number of grams of the substance associated with the transfer of "n" electrons or protons or with the neutralization of "n" negative or positive charges, where "n" is Avogadro's number, 6.02×1023.

In a practical sense, a gram equivalent is the amount of a compound that is necessary to produce a given normality of a "reactive species" in a solution. Here, reactive species include ions that will precipitate, neutralize base (protons, H+), neutralize acid (hydroxide, OH-), donate electrons, or accept electrons. To make clear the distinction between grams and gram equivalents, consider the following:

When making a solution with a given molarity, you measure grams of a compound and dissolve them in a known volume.

When making a solution with a given "'normality, you measure "gram equivalents" of a compound, "in grams", and dissolve them in a known volume.

It is important to note that gram equivalents are specific to a given ion "in solution" (e.g., Na+, OH-, Ca2+, Fe3+, etc.), as measured "in the solid state". As such, it can be a measure of ions participating in one of three general categories of reactions: oxidation-reduction reactions, acid-base reactions, and precipitation reactions:

*In acid-base chemistry, the gram equivalent expresses the mass of acid or base which will furnish a concentration of protons or hydroxide ions undergoing neutralization.

*In redox reactions, gram equivalents denote the mass of oxidizing or reducing agent that can accept or furnish a given molarity of electrons.

*In precipitation reactions, the gram equivalent is mass of a substance (typically a salt) which will produce a molar concentration of ions that participate in the precipitation.

References

* Meldrum, W.B. "J. Chem. Ed.", 1955, "32", 48.


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  • gram-equivalent weight — gram equivˈalent or gram equivalent weight noun The quantity of a substance whose mass in grams is equal to its equivalent weight • • • Main Entry: ↑gram …   Useful english dictionary

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  • gram equivalent — noun the amount of a substance, in grams, that is numerically equivalent to its equivalent weight …   Wiktionary

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