Milliequivalent weight

The concentrations of electrolyte solutions are generally expressed in chemical units known as milliequivalents (mEq). The milliequivalent weight represents the amount, in milligrams, of a solute equal to 1/1000 of its gram equivalent weight. A milliequivalent is a unit of measurement of the amount of chemical activity of an electrolyte. A milliequivalent unit is related to the total number of ionic charges in solution and it takes the valence of the ions into consideration. Table 5.1 provides valence, atomic and milliequivalent weights, and formulae of selected ions. 

TABLE 5.1. Valance, Atomic and Milliequivalent Weights, and Formulae of Selected Ions... 

Ion Valence Atomic Weight Milliequivalent Weight Formula... 

Weight of the substance in mg = Number of milliequivalents x Milliequivalent weight... 

Where V is volume of sodium hydroxide solution used for titration (ml) N is normality of sodium hydroxide solution meq. wt. is milliequivalent weight of the standard and v is sample volume (ml). 

This procedure was tested using both amine picrates and amine oxide picrates. The milliequivalent weights of the picrates determined were within 1% of the theoretical value. 

As a consequence, stoichiometric ratios such as those described in Section 13C-3 (page 343) need not be derived every time a volumetric calculation is performed. Instead, the stoichiometry is taken into account by how the equivalent or milliequivalent weight is defined. 

Note that the milliequivalent weight of the Fe2+ is equal to its millimolar mass. The percentage of iron is... 

Note that the milliequivalent weight of Fe304 is one third its miUimolar mass because each Fe undergoes a one-electron change and the compound is converted to 3Fe + before titration. The percentage of Fe304 is then... 

The number of milliequivalents of (NH4)2C204 is equal to the number of milliequivalents of NH3 and N, but the milliequivalent weight of the (NH4)9C204 is equal to one half its molar mass. Thus,... 

By definition there are 1000 milliequivalent weights (meq) in one equivalent weight of an acid or base. Normality may also be represented as... 

A milliequivalent weight is often referred to simply as a milliequivalent (meq). 

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