[sachabinky]

While trying to prepare CoSO4 from the metal by dissolution in 98% H2SO4, i put 15g of the metal into an excess of acid, - approx 120ml , which proceeded slowly, until i added some water, maybe 100ml which has almost dissolved the lot.
As the volume decreases upon boiling, i see some pink chunks of soft precipitate form at the edges of the beaker, which break up on stirring, but am wondering if i will ever get a completely dry powder, since i didn't get the exact stoichiometry. (too much acid Ratio)
I've turned off the heat for tonight and put it on hold till tomorrow.
From the limited info i've gathered, i see that often, salts are precipitated by substitution reactions from their ionic metal solutions, and maybe i should have done this another way.
My main goal was to get a combination mixture of cobalt sulphate 70% and Cobalt chloride 20% (to be made separately, but now i wonder if i could just adjust this reaction, by addding appprox 30mlof HCl 37.5%, getting approx 20% of total moles being the Chloride, and just use that solution for my electroplating experiment/
Is there still a way to get the cobalt sulphate powder, even after i have exceeded the ammount of H2SO4?-
I'm guessing i might have to add more cobalt metal to use up the extra acid.
any advice would be appreciated , thanks.


By calculations below,

Co = 58.9331g/mol

CoSO4 = 154.996 g/mol
H2SO4 = 98.079 g/mol density = 1.84

Ratio = 1:1
at 15g Cobalt- we are expecting 39.45g
of CoSO4 to be produced.

Electroplating Mixture
70% CoSO4
20% CoCL2
10% BH3O3

[chenbeier]

Cobalt sulfate will crystallize as hydrate. CoSO₄ * 7 H₂O.
If you ad hydrochloric you will get blue chlorocomplexes.

[Arkcon]

Yes, sachabinky:, something must be in excess, to get complete reaction.  For sulfuric acid, any excess will always be sulfuric acid of syrupy consistency, once you dry away excess moisture.  You idea to use excess cobalt is a better one, but what you ought to do is prepare a great excess, then recrystallize.

[sachabinky]

Thanks for those tips, that helps to reassure me .I'm still wondering how to clean the surupy Sulfuric off, since that is what i feared would happen.
I'll be looking for a certain alcohol or other solvent, that CoSo4 is insoluble in,- in that case.

I separated the pink liquid/Powder produced so far, and topped up the remaining metal with fresh Acid/Water Mixture.
It seems to be progressing toward total dissolution with heat and stirring.
It would be best to work with powdered cobalt i realize, after this slow result.
I have ordered some of that anyhow.



The plan for the Cobalt Chloride is to dissolve straight into HCl, 37.5%., .
It seeems to make sense.

[sachabinky]

All Co now in solution, settling as fine pink precipitate, too fine to filter in any way, so still waiting for the fine Co powder to arrive in order to add the excess.
Once excess H2SO4 is converted, looks like Methanol is the best candidate for recrystallization.

[sachabinky]

All done!!.
Didn't worry about recrystallization from Methanol,though i could do that later.
I just used an excess of Co powder, as discussed-and water, waited a week, then filtered and boiled the filtrate to low volume and let cool to precipitate the nice bright pink powder.
Thanks for your help.
Thread closed... for me.