Some observations on potassium dichromate as an oxidimetric standard

The stoicheiometry of the reaction of iron(II) with chromium(VI) and the suitability of potassium dichromate as a primary standard have been examined. To differentiate the effects of possible non-stoicheiometry and impurities in the samples, several different sources of chromium(VI) and three different standardisation schemes, based on the use of arsenic trioxide, sodium oxalate and potassium iodate, have been used. It is shown that the stoicheiometry of the reactions is satisfactory and that suitable grades of potassium dichromate are excellent primary standards.