A precipitação do estrôncio na forma de cromato em meio amoniacal e hidroalcoolico

Abstract

This paper describes the data obtained concerning qualitative and quantitative analyses of the precipitate formed when to a solution containing strontium ion are added potassium dichromate, ammonium hydroxide and 95 per cent alcohol. Three replications of standard solution containing 1.8, 4..4, 8.8, 13.7, 27.5, 41.2, and 50.5 mg of strontium were treated with potassium dichromate and then, with constant stirring 95 per cent of alcohol and ammonium hydroxide. The precipitate was allowed to stend for two hours and afterward was centrifuged, washed with 95 per cent alcohol dried at 80ºC for 14-16 hours and weighed. Qualitative analysis of the precipitate showed potassium and ammonium ions, besides strontium and chromate. The relationships between the weight of strontium and the weight of the precipitate obtained is given by the regression line expressed by the equation: Y = 5.48 + 0,84, where X, is the weight of strontium in milligram Y, is the weight of the precipitate in milligram The value 4, 58 for the B parameter of the regression equation and the qualitative and quantitative analysis of the precipitate, suggested that its composition must be quite different from the simple strontium chromate SrCr0(4). The data allow to admit the following probable composition: 6 SrCrO4 . (NH4)2CrO4 . 6K2CrO4