Preparation of potassium hexacyanochromate(III)
42g of chromium(III) acetate 1-hydrate are dissolved in 180ml of water. The obtained solution of the chromium(III) salt is poured into a boiling solution of 75g of potassium cyanide in about 300ml of water. Two grams of activated charcoal are added, and after stirring the hot mixture for several minutes it is filtered and evaporated to 300ml on a steam bath in an evaporating dish. The hot solution is treated with charcoal as before and filtered while hot. On cooling in ice, the product crystallizes out as pale-yellow needles. The material is suction filtered and pressed well. The mother liquor is further evaporated to obtain two or three more crops of product. After draining off the main aqueous liquor, each batch of crystals is thoroughly washed with two 25ml portions of 95% alcohol, and dried in a desiccator away from light. To obtain a pure product (the crude material is satisfactory for most purposes) two or three crystallizations from water (not over 60°C) are necessary. Precipitation from aqueous solution by alcohol is somewhat less satisfactory. Total crude yield about 35 grams. The solubility of the complex salt in water is about 31g/100ml at 20°C.
Inorganic laboratory preparations, by G. G. Schlessinger, 82-83, 1962
Potassium hexacyanochromate(III), AKOS022185826, AK142819