HIGH-FREQUENCY TITRATIONS: I. ARGENTIMETRIC DETERMINATION OF HALIDES AND THIOCYANATE IN METHANOL

A new method is proposed for the determination of milligram amounts of each halide present in a mixture of alkali-metal halides. In some mixtures, thiocyanate also may be determined. A methanol solution of the sample is titrated in a closed-type cell, with a standard solution of silver nitrate in methanol. By using high-frequency titrimetry, and an appropriate concentration of the halide solution, sharp end points were obtained for each halide. Because of solid solutions, the accuracy of the determination of individual halides in mixtures depended on the mole ratios of the halides; the errors found in the titration of various binary, ternary, and quaternary mixtures are reported. For some binary mixtures, the total amount of halide titrated in 120 ml of methanol was varied from 0.5 to 500 micromoles. At the lower concentrations, addition of a small amount of sodium nitrate sharpened the end point. At all concentrations of halide, an excessive amount of indifferent electrolyte essentially eliminated the end points. The alkali-metal halides gave more satisfactory titration graphs than did some other metal halides. The effects of variation in temperature, and of solvent evaporation were noted.