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standard solution[¦stan·dərd sə¦lü·shən]
a solution with a known concentration of chemical reagent. Standard solutions are used in titrimetric analysis for establishing the quantity of a particular substance (analyte) by titrating to an equivalence point, usually determined by a change in color of a chemical indicator or of the titrated solution. In order to calculate the results, the amount (volume, sometimes weight) of the standard solution consumed in the reaction with the analyte is established. The accuracy of the determinations depends on the accuracy in establishing the concentration of the standard solution. The concentration of a standard solution is usually expressed in terms of normality. The titer also has certain practical applications.
Standard solutions are obtained in a number of ways. One method involves dissolving an exact weight of a substance in an exact volume of solvent. The substance must be chemically pure and must be stable during storage in solid form and in solution; the composition of this substance must correspond exactly to its chemical formula. A second method involves titration with another solution having a known concentration. This method is convenient in that it does not require exact weighings to determine the concentration of many solutions. Standard solutions can also be prepared by using titrants in the form of dry substances or solutions in amounts required for the preparation of 1 liter of solution of a given concentration. These titrants are produced industrially and are marketed in sealed glass ampuls. Standard solutions must be stored under conditions that ensure a constant composition; here, the chemical nature of the solute must be taken into account.
REFERENCESKolthoff, I. M., and V. A. Stenger. Ob’emnyi analiz, vol. 1. Moscow-Leningrad, 1950. (Translated from English.)
Kreshkov, A. P. Osnovy analiticheskoi khimii, 3rd ed. [vol. 2]. Moscow, 1970.
Alekseev, V. N. Kolichestvennyi analiz, 4th ed. Moscow, 1972.
L. V. NIFANTEVA