Potassium Dichromate from Chromium Metal or Cr(III)

by Nitro

Hey chemists out there! This is a new synthesis of POTASSIUM DICHROMATE, a potent oxidizer which can be used to make GOOD things. I cannot give you refs cause I have discovered this myself. The idea came from a german chemistry lexikon, Römpp's, which said that Cr(OH)3 reacts with NaOH/H2O2 to form chromate.


This file was written for informational purposes only. You should not attempt to make it and to use this controlled (in Europe it is) stuff to make illegal drugs or to poison someone. :) :) Potassium dichromate is toxic. A dose of 4-10 g of it can and will cause the death of a man if ingested.

Starting material can be:

  • Chromium metal
  • Chrome-nickel wire
  • Any Chromium(III) salt


Weigh out 104 g Chromium metal and dissolve it in 500 ml of fuming (37%) HCl (or equimolar amount of dilute H2SO4) in a preferably large beaker. Add the metal to the acid in small portions and warm if the rxn goes too slowly. When it's all dissolved, filter the solution to remove insoluble material the chrome was contained with. In another beaker, dissolve 245 g pure NaOH in enough water and let the solution cool to 20-40°C. Add this alkali solution slowly to the filtered chromium(III)-chloride solution. A greenish or grayish precipitate of Cr(OH)3 will form. Filter this, squeeze it out and wash it 3 times with distilled water. You don't need to dry it, just put it into a clean beaker and add: 1) a solution of 160 g NaOH in just sufficient water and 2) approx. 350 ml of 30% hydrogen peroxide. Add the reagents carefully for that they don't splash. The green Cr(OH)3 will dissolve and the soln will turn a very beautiful yellow of sodium chromate. If you boil the solution for some time and then crystallizate it, you can get Na2CrO4, but we want to proceed to potassium dichromate now.

Add 164 ml of concentrated HCl. The color will immediately change to orange. This is the color of the Cr2O72- anion. Now boil the solution down to approx. 50% its original volume. After cooling white crystals of NaCl can be removed and discarded.

Now weigh out 149 g of Potassium chloride (or equimolar amount of either K2CO3, KOH, or KNO3). Dissolve it in 80°C hot water to prepare a hot saturated solution. Pour this solution into the orange solution of sodium bichromate. Orange crystals of the crude product will form. Filter them after cooling to 10°C.

Recrystalizate the product twice from distilled water. Store in well-stoppered bottle.

If you started from chrome-nickle, then some insoluble nickle(II)-hydroxide will remain undissolved after adding NaOH/H2O2. This can be filtered. If you had Cr(III)-salts, then just dissolve them in water and add NaOH soln.

The solubility of K2Cr2O7 is only 7 g/100 g water, but that of Na2Cr2O7 is more than 100 g/100 g. Therefore, if you add a potassium salt solution to Na2Cr2O7 soln, K2Cr2O7 will crystallizate readily.

The yield of this synth is almost quantitative, around 280-290 g if you did it right (>95%). There is only loss of material which remains on the filter etc.