• British Pharmacopoeia Volume V
  • Appendices
  • Appendix I A. General Reagents

Potassium Dichromate
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Potassium Dichromate Dipotassium dichromate; K2Cr2O7 = 294.2 (7778-50-9)

Analytical reagent grade of commerce.

Potassium dichromate used for the calibration of spectrophotometers contains not less than 99.9% of K2Cr2O7, calculated with reference to the substance dried at 130°.

Assay Dissolve 1 g in sufficient water to produce 250 mL. Add 50 mL of this solution to a freshly prepared solution of 4 g of potassium iodide, 2 g of sodium hydrogen carbonate and 6 mL of hydrochloric acid in 100 mL of water in a 500-mL flask. Stopper the flask and allow to stand protected from light for 5 minutes. Titrate with 0.1m sodium thiosulfate VS using 1 mL of iodide-free starch solution as indicator. Each mL of 0.1m sodium thiosulfate VS is equivalent to 4.903 mg of K2Cr2O7.