Titrimetric Analysis

a method of quantitative analysis based on the measurement of the volume of a solution with a precisely known concentration of a reagent (the titrant) required for reaction with a given amount of a substance being determined (the analyte). Among the means used in titrimetric analysis are complexing and precipitation, acid-base, and oxidation-reduction reactions. The main requirements for the reactions used in titrimetric analysis are high speed, the presence of stoichiometric proportions, and the absence of side reactions, which distort the results of analysis. Several methods are available for titrimetric analysis.

In direct titration, a sample of the analyte is titrated with a standard solution, the titrant, to the equivalence point, which is the point at which the amount of the standard solution is equivalent to the amount of the analyte according to the chemical equation for the given reaction. The end of titration is determined visually, from the changing in color of an added indicator, or using instruments. The more exact the determination of the equivalence point, the smaller the analytical error. The calculation is made from the formula

P = 0.001. N · v · E

where P is the mass, E is the number of gram equivalents of the analyte, N is the normality, and v is the volume (in milliliters) of the standard solution.

Back titration is used when the analyte either does not react with the standard solution or reacts too slowly. In this event, a previously known excess of the standard solution is added to the analyte, and the residue after reaction with the substance in question is titrated with another standard solution.

Titration by substitution is used when direct titration of the analyte is difficult, as is the case when no suitable titrant or essential indicator is available. In this event, a reaction with an undetermined excess of a suitable reagent is used to convert the analyte into another compound, which is titrated by the standard method as described above. For example, the amount of potassium bichromate in a solution is determined by this method.

In addition to water, the following organic solvents are used in titrimetric analysis: hydrocarbons and their halogen derivatives, alcohols, ketones, acids, amines, amides, and nitryls. These solvents make possible expansion of the range of analytes, because titrimetric analysis can be based on reactions that do not occur in water or that do not produce clear-cut end points—for example, weak acids or bases or mixtures of acids or bases of similar strength. The determinations made in nonaqueous solutions are usually more exact than those made in aqueous solutions, because the drops of organic liquids are smaller than in aqueous solutions as a result of low surface tension.