20
Stoichiometry IV: Equivalent Weight
and Normality
The stoichiometric calculations of Chapters 12 and 13 are based on the mole as
the fundamental chemical unit in reactions. An alternative method of calculation utilizes the equivalent as a fundamental chemical unit. There are two kinds
of equivalents, the type depending on the reaction in question; we shall refer to
them as acid-base equivalents (or simply as equivalents) and electron-transfer
equivalents (or E-T equivalents). The concept of an equivalent is particularly
useful when dealing with complex or unknown mixtures, or when working out
the structure and properties of unknown compounds. In addition, it emphasizes
a basic characteristic of all chemical reactions that is directly applicable to all
types of titration analyses.
ACID-BASE EQUIVALENTS
The acid-base equivalent is defined as the weight (in grams) of a substance that
will provide, react with, or be equivalent to 1 mole of H
+ . Thus, 1 mole (98.1
g/mole) of H 2 SO 4 contains 2 moles of H
+ , and its acid-base equivalent weight is
49.05 g/equiv. One mole (171.4 g/mole) of Ba(OH) 2 contains 2 moles of OH"
and will react with 2 moles of H
+ ; its acid-base equivalent weight therefore is
85.70 g/equiv. For 1^(804)3, there are 6 equivalents/mole, because the 2 La
3+
ions provide the same total positive charge as 6 H
+ ; the equivalent weight is i of
the mole weight.
Stoichiometry IV: Equivalent Weight
and Normality
The stoichiometric calculations of Chapters 12 and 13 are based on the mole as
the fundamental chemical unit in reactions. An alternative method of calculation utilizes the equivalent as a fundamental chemical unit. There are two kinds
of equivalents, the type depending on the reaction in question; we shall refer to
them as acid-base equivalents (or simply as equivalents) and electron-transfer
equivalents (or E-T equivalents). The concept of an equivalent is particularly
useful when dealing with complex or unknown mixtures, or when working out
the structure and properties of unknown compounds. In addition, it emphasizes
a basic characteristic of all chemical reactions that is directly applicable to all
types of titration analyses.
ACID-BASE EQUIVALENTS
The acid-base equivalent is defined as the weight (in grams) of a substance that
will provide, react with, or be equivalent to 1 mole of H
+ . Thus, 1 mole (98.1
g/mole) of H 2 SO 4 contains 2 moles of H
+ , and its acid-base equivalent weight is
49.05 g/equiv. One mole (171.4 g/mole) of Ba(OH) 2 contains 2 moles of OH"
and will react with 2 moles of H
+ ; its acid-base equivalent weight therefore is
85.70 g/equiv. For 1^(804)3, there are 6 equivalents/mole, because the 2 La
3+
ions provide the same total positive charge as 6 H
+ ; the equivalent weight is i of
the mole weight.