VARIABLES IN STANDARDIZATION OF CERIC SOLUTIONS AGAINST ARSENIOUS OXIDE

The standardization of ceric solutions against arsenious oxide primary standard has been investigated. The standardization of ceric sulfate is not direction dependent. Accurate standardizations are obtained when arsenious oxide is titrated with ceric sulfate solution and also in the reverse direction when ceric sulfate solution is titrated with standard arsenious oxide solution. The concentrations of osmium tetroxide catalyst and sulfuric acid do not affect the accuracy of the standardizations. However, the standardization of ceric ammonium nitrate solution is direction dependent. Accurate standardizations are obtained when ceric ammonium nitrate solution is titrated with standard arsenious oxide solution. The concentrations of osmium tetroxide catalyst and sulfuric acid cause no noticeable effect upon the accuracy of the standardizations. The direct titration of arsenious oxide with ceric ammonium nitrate deviates from the anticipated smooth single-break potentiometric titration curve. The deviations and resulting inaccuracies were traced to a nitrate interference. In the direct titration with ceric ammonium nitrate the concentrations of osmium tetroxide catalyst and sulfuric acid were observed to be secondary contributions to the deviations. Several alternate procedures for the standardization of ceric solutions are described. © 1969, American Chemical Society. All rights reserved.