Potassium Dichromate

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 thiosulphate VS using 1  ml of iodide-free starch solution as indicator. Each  ml of 0.1m sodium thiosulphate VS is equivalent to 4.903  mg of K₂Cr₂O₇.