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Molecular Weight Calculator Molecular Weight Calculator

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The molecular weight of an acid or base can be obtained from the molecular formula, data tables, or the label on the bottle containing the acid or base of interest. For bases, the number of equivalents per mole is the number of OH − ions contributed by the base per mole of base. For acids, the number of equivalents per mole is the number of H + ions contributed by the acid per mole of acid. It is calculated by dividing the molecular weight of solute by the number of equivalents per mole of solute (Equation 2).

EW is the equivalent weight in g/equivalent.

Note that V is the final or total volume of solution after the solute has been added to the solvent.

V is volume of solution in liters (L) in which the indicated mass ( m) of solute must be dissolved to make the desired normal concentration ( C N).

m is the mass (i.e., weight) of solute in grams (g) that must be dissolved in volume V of solution to make the desired normal concentration ( C N).

Using SI prefixes, the concentration may also be expressed in different fractions of the normal concentration such as milliequivalents/L (mN), microequivalents/L (μN), nanoequivalents/L (nN), picoequivalents/L (pN), etc.

The normal concentration ( C N) is always equal to or greater than the molar concentration ( C M) (Equation 3). A 1 N solution is one in which exactly 1 equivalent of solute is dissolved in a total solution volume of exactly 1 L. Normality is defined as the number of equivalents of solute dissolved per liter of solution (equivalents/L = N) (Equations 1, 3, and 4). This is also referred to as normality, which is used to express the concentration of a solute in a solution. C N is the normal concentration in equivalents/L (Normal or N).

While it is more appropriate to refer to equivalent weight as equivalent mass, this term is rarely used. Because 1 mole of acid or base is equal to 1 equivalent of acid or base, equivalent weight is expressed in grams per equivalent (g/equivalent or g/eq) (Equation 2). Another way of expressing this is that the equivalent weight is defined as the mass (in grams) of a base that reacts with exactly 1 mole of hydrogen ions (H +). For bases, the equivalent weight is defined as the mass (in grams) of a base that provides exactly 1 mole of hydroxide ions (OH −) to a reaction. Another way of expressing this is that the equivalent weight is defined as the mass (in grams) of an acid that reacts with exactly 1 mole of hydroxide ions (OH −). For acids, the equivalent weight (EW) is defined as the mass (in grams) of an acid that provides exactly 1 mole of hydrogen ions (H +) (to be precise, hydronium ions, H 3O +) to a reaction. Similar to molarity, where the molecular weight (MW) is used for calculating the molar concentration, for normal solution concentrations, it is desirable to use the equivalent weight (EW). Thus, in order to have a one-to-one relationship between acids and bases, many chemists prefer to express the concentration of acids and bases in normality. Normality is used in place of molarity because often 1 mole of acid does not neutralize 1 mole of base. Normality is defined as the number of equivalent weights (or simply equivalents, eq) of solute dissolved per liter of solution (equivalents/L = N) (Equation 1).

In some cases, particularly in situations involving acid-base chemistry, the solution concentration is expressed in normality (N or C N).