We want to use Chromic Sulphate (Cr2(SO4)3.6H2O) to contaminate soil, however we found it not to be soluble in water while according the literature and tanning practices this should be soluble in water. How can this be?
The anhydrous salt of chromic sulfate is insoluble in water and acids but dissolves to form complexes when reducing agents are added; the hydrated salts are soluble in water; the pentadecahydrate is insoluble in alcohol, but the octadecahydrate dissolves in alcohol. Your chromic sulphate is probably the anhydrous and not the hydrated form. Tie up with the company. Just a little mix-up i want to believe.
Thank you Maurice. I was aware of the difference in solubility between the hydrated and anhydrous Chromium salt, but the chemical we obtained states clearly that it is the hydrated form, Cr2(SO4)3.6H2O. Any other possibilities perhaps?
It should be soluble in concentrated sulfuric acid, which could then be diluted. However be aware that the solution is a very strong oxidizing agent (it used to be widely used for cleaning chemical glassware) and will be reduced to green Cr(III) on adding it to soil. Cr(VI) ion is also now considered carcinogenic so its salts are no longer used where alternatives are available.
The hydrated form should be bright orange with distinct crystals. The unhydrated form is a different shade (darker from memory) and a powder.
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