Foeskes - 11-10-2017 at 05:25
I am going to try to separate nickel from chromium.
I'm thinking of using either reacting their hydroxides(Ni(OH)2 and Cr(OH)3) with sodium hypochlorite or sodium hydroxide to dissolve the chromium and
precipitating the nickel hydroxide. Although the I'm not sure if the nickel hydroxide will react with those or if the chromium has trouble dissolving
or something, since I can't really find that much information on it.
ninhydric1 - 11-10-2017 at 07:54
Nickel hydroxide shouldn't dissolve in NaOH solution, but chromium hydroxide will react with NaOH to form sodium chromate.
Foeskes - 11-10-2017 at 14:29
Doesn't Sodium hydroxide react to form chromite?
And what about hypochlorite?
ninhydric1 - 11-10-2017 at 14:59
Chromates are chromites, just that chromate is the more common and more widely used nomenclature. Sodium hypochlorite will also dissolve chromium
oxide. Note that these reactions occur slowly so adding hydrogen peroxide will speed the reaction up.
woelen - 11-10-2017 at 22:35
Sodium hypochlorite reacts with nickel hydroxide. A black insoluble compound is formed, most likely a nickel(III) compound. I think it is hydrous
Ni2O3.
Sodium hypochlorite also reacts with chromum hydroxide. It reacts with formation of a yellow solution of sodium chromate. This contains hexavalent
chromium in the CrO4(2-) ion.
wg48 - 12-10-2017 at 00:04
Nickel chromate is insoluble. So some of the nickel hydroxide may be converted nickel chromate in the presence chromate ions. Perhaps with a high ph
(large excess of alkali) it will not be very much or sufficiently slow that reasonable separation of the soluble chromate can still be achieved.
Foeskes - 12-10-2017 at 16:50
So is sodium hydroxide the most ideal for dissolving the chromium and leaving the nickel behind?
According to Wikipedia:chromites are chromium in its third oxidation state(Na2Cr2O4) and chromates are chromium in its sixth(Na2CrO4)
ninhydric1 - 12-10-2017 at 17:58
Oh, my mistake then. Chromium chemistry can be a bit confusing 
.
DraconicAcid - 12-10-2017 at 18:32
Yes, separate chromium from nickel with sodium hydroxide.