Preparation and Analysis of K3 Cr

1 Preparation and analysis of K3(Cr(C204)3].3H20 (Inorg.SynthA 939) 37) This can be prepared by the reduction of potassium dichromate with oxalic acid in presence of oxalate. It is envisaged that the first stage is the reduction of CKVI) to Cr(III), followed by the complex formation with the oxalate. 

Dissolve 8.8 g H2C2O4.2H2O in 25 cm warm water. Add gradually 3.0 g of finely ground When the vigorous reaction has subsided, heat nearly to boiling and 

Recrystallise from water/ethanol mixture, wash with alcohol and ether and dry by continued suction. 

When the solid is boiled with KOH solution, it decomposes the complex anion precipitating Cr(lII) hydroxide. On filtering this off, die acidified filtrate containing the oxalate, is determined by titration with permanganate. 

Heat an exactly weighed amount of the preparation at 110 C to a constant weight to determine the % of water of crystallisation. 

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