Some General Points Concerning Titrations
Titrimetric analysis is most likely the oldest method of quantitative analysis. Its commonplace use has continued to date, due to its great simplicity of use and low cost. It is an absolute method to determine a quantity of matter. It is often used in off
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Some General Points Concerning Titrations
Titrimetric analysis is most likely the oldest method of quantitative analysis.1 Its commonplace use has continued to date, due to its great simplicity of use and low cost. It is an absolute method to determine a quantity of matter. It is often used in official methods as well as in reference methods of analysis, but it has equal success as a routine quantitative method of analysis.
7.1
General Principle of Titrimetric Methods
Titrimetry permits us to determine a compound’s concentration in a given solution by quantitatively measuring the quantity of reactant reacting with it. Let us titrate a compound A in a solution at concentration CA . Increasing and known volumes of its reactant B at concentration CB are added to an exactly known volume VA of solution A. B is chosen to react quantitatively with A according to a stoichiometric reaction. Let us call VBf the added volume when the reaction has just completed. The quantity of B that has disappeared is VBf CB . This is also the quantity of A that was initially present in the solution to analyze (after having taken into account the reaction stoichiometry). Then the determination of CA becomes immediate. For example, if one molecule of A reacts with one molecule of B (a one-to-one reaction stoichiometry), we find VACA = VBf CB , CA = VBf CB /VA .
(7.1)
VBf is accessible via any experimental means that indicates the end of the titration reaction; CB and VA are known. 1
Joseph Gay-Lussac (1778–1850) seems to have been the first chemist to give the status of exact quantitative analysis method to titrimetry after his work in 1824 devoted to the determination of active chlorine, potassium hydroxide, and silver ion. Other chemists in this field must also be mentioned. We shall be content here with recalling Karl Friedrich Mohr (1800–1879) and Carl Remigius Fresenius (1818–1897).
J.-L. Burgot, Ionic Equilibria in Analytical Chemistry, DOI 10.1007/978-1-4419-8382-4_7, © Springer Science+Business Media, LLC 2012
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7 Some General Points Concerning Titrations
7.2 Terminology The solution of A is called the titrand solution, and that of B is the titrant solution. In some countries (France, for example), a solution is called titrated if it contains a known amount of substance in a known volume. The titer of a solution is the reactant proportion (and thus the solvent proportion) in the solution. In the largest sense, it means its concentration (see Chap. 1). In a more restrictive sense, it is the solute concentration expressed in mol/L or its normality (see Sect. 7.3). The titrant solution must be standardized before the titration. In other words, its titer must be precisely known. (In certain countries, a “standard solution” is purely and simply what we called a titrated solution above). The standardization of the titrant solution is achieved by its titration with a standard solution. This can be a primary or secondary (standard) solution. A primary standard solution is prepared simply by weighing the reagent in the pure
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