Equivalent (chemistry)
In chemistry, an equivalent is a measure of how much of a substance is needed to react with or produce one mole of another substance.
The equivalent mass of a compound is the mass of one equivalent. Unlike molar mass, which is a property of a compound, equivalent mass of a compound depends on the reaction being used as a reference.[1]
Example
[change | change source]The Arrhenius acid-base theory treats acids and bases as equivalents of the hydrogen and hydroxide ions. The table shows the acid-base reactions of two different bases and three different acids:
| NaOH | Ca(OH)2 | |
|---|---|---|
| HCl | HCl + NaOH → NaCl + H2O | 2 HCl + Ca(OH)2 → CaCl2 + 2 H2O |
| H2SO4 | 2 NaOH + H2SO4 → Na2SO4 + 2 H2O | Ca(OH)2 + H2SO4 → CaSO4 + 2 H2O |
| H3PO4 | 3 NaOH + H3PO4 → Na3PO4 + 3 H2O | 3 Ca(OH)2 + 2 H3PO4 → Ca3(PO4)2 + 6 H2O |
One HCl and one NaOH make one H2O, so we say that hydrochloric acid is one equivalent of acid and sodium hydroxide is one equivalent of base. When HCl reacts with Ca(OH)2, twice as much acid is used to produce twice as much water: Ca(OH)2 is two equivalents of base. One unit of phosphoric acid makes three units of water, H3PO4 has three equivalents of acid.
References
[change | change source]- ↑ Douglas A. Skoog, Donald M. West, F. James Holler, Stanley R. Crouch (2013-01-01). Fundamentals of Analytical Chemistry. Cengage Learning. p. 394. ISBN 9781285607191.
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