chromic acid

[akcapr]

Is it possible to make chromic acid or chromic oxide/trioxide from ammonium dichromate?

[woelen]

Don't try to do that with ammonium dichromate. You need K2Cr2O7 or Na2Cr2O7.2H2O. In fact, ammonium dichromate is not a very interesting chemical, except for the volcano demo and some pyrotechnics things. For all aqueous and solution chemistry, the sodium- and potassium salt are MUCH more useful. The ammonium ion is prone to oxidation, when mixed with CrO3 and that can give rise to really dangerous situations.

 

Btw, why do you want CrO3? Almost all experiments with CrO3 can also be done by dissolving K2Cr2O7 in dilute H2SO4. CrO3 is a pain on storage. I have 25 grams of this, but within a year it has become a bad black/brown, sticky and exceedingly corrosive mass. My K2Cr2O7 already is 20 years old and it still is a beautiful bright orange crystalline solid, which shows no deterioration at all. My (NH4)2Cr2O7 also keeps very well.

 

Even, although I have CrO3, I hardly use it, because K2Cr2O7 is a much safer and easier to handle alternative. CrO3 is so corrosive, that it ignites organics and immediately destroys your skin on contact. Beware of all hexavalent chromium compounds. They most likely are carcinogens.

[akcapr]

I wanted it for organic oxidation. Not the explosive kind, but the subtle alcohol too -COOH. And possibly for other organic things.

[budullewraagh]

permanganate does it just as well