Sciencemadness Discussion Board

cobalt nitrate

itchyfruit - 12-7-2009 at 13:01

According to wiki cobalt nitrate should be orange/red,mine on the other hand is purple,can anyone explain?
My cobalt chloride is blue which seems about right.

JohnWW - 12-7-2009 at 13:12

It would depend on whether it is a salt of Co(II) or Co(III), as well as on the chemical environment of the Co cation. I have seem a quantity of a Co(II) salt, I think it was the sulfate although I may be wrong, which was magenta (reddish-purple) in color. CoO incorporated into a siliceous environment, as in stained glass (smalt) and glazes, is deep blue in color.

itchyfruit - 12-7-2009 at 13:28

I made it by heating cobalt oxide and nitric acid, as per wiki info,but theirs is redish:( allthough i do like the purple colour!!

Polverone - 12-7-2009 at 13:32

Itchyfruit, I earlier merged your thread into the short questions thread since it was just that, a short question. You should be able to see your earlier post about this same topic on the last page of that thread.

In the future, if you have a short question, please use the short questions thread.

Jor - 12-7-2009 at 13:41

I have the sulfate, chloride and nitrate.
Cobalt chloride hexahydrate is dark red and the anhydrous salt (i made this by very slow heating and driving off water) is light blue.
Cobalt sulfate heptahydrate is lighter than the chloride, it is pink/light red.
The nitrate, wich I made by dissolving pure cobalt in nitric followed by evaporation is red.

None of these is purple.

Co(III) is the favored species when the correct ligands are present (wich does not include aqua or chloro-ligands for example), while otherwise Co(III) is an extremely strong oxidiser, rapidly oxidising water to oxygen.

itchyfruit - 12-7-2009 at 15:23

Thanks Polverone i didn't realise their was a short question thread, but as of now i shall use it.
What should i do if i think my short question may need a long answer ?
I tried again using cobalt sulphate and nitric acid and it's redish so i'm not sure what the purple stuff is !!

woelen - 13-7-2009 at 13:39

I also had cobalt nitrate (made by dissolving very pure cobalt metal in reagent grade nitric acid and then evaporating and slowly crystallizing) and this is reddish/purple with a brown tinge. It definately is not pure purple, I would call it red, like Jor said, but it is not a bright red color.

Jor - 13-7-2009 at 13:59

Had? :P

JohnWW - 13-7-2009 at 18:22

Quote: Originally posted by woelen  
I also had cobalt nitrate (made by dissolving very pure cobalt metal in reagent grade nitric acid and then evaporating and slowly crystallizing) and this is reddish/purple with a brown tinge. It definately is not pure purple, I would call it red, like Jor said, but it is not a bright red color.
Magenta, as I said above; particularly equivalent to magenta dye or process magenta in color, with approximately 2 parts red to 1 part blue, see http://en.wikipedia.org/wiki/Magenta
Salts of ferrate(VI) are also similar in color, being somewhat more reddish than permanganate(VII).

[Edited on 15-7-09 by JohnWW]

woelen - 14-7-2009 at 12:45

Quote: Originally posted by Jor  
Had? :P
Yes, had. I have donated it to someone, who did not have any cobalt salts. Having the sulfate already and the chloride and potteries grade carbonate and the pure metal I decided I did not need another cobalt salt. I just made it (only 5 grams or so) to see how well it crystallizes and how pure I can get it (and it can be obtained fairly easily at good purity).

@JohnWW: Yes, indeed magenta is a good description of the color, but it is not as bright as in the Wiki-page. My cobalt nitrate can be regarded as magenta, but greyed out/shaded.

[Edited on 14-7-09 by woelen]

itchyfruit - 14-7-2009 at 15:19

The nitrate sample i made with cobalt sulphate is redish but turns blue when heated then back to red when it cools down.

woelen - 15-7-2009 at 13:09

Are you sure it is a pure nitrate. The material I had did not turn blue on heating. Only the chloride shows this reversible reaction. The hydrated chloride becomes very deep blue/indigo when heated and on cooling down it becomes reddish/purple again.

itchyfruit - 15-7-2009 at 15:36

No i'm not really, as i made it myself and as you can tell i'm not much of a chemist :) The nitric acid is 70% lr grade from a fairly well known chemical company, the cobalt sulphate i'm not to sure about, it came via ebay and it don't look to great.
If i get a chance tomorrow i'll pop down the local pottery supply shop and get some cobalt carbonate and give it another try, i'm not sure the sulphate is any good for this purpose as i can't see how it can neutralise the acid to form a salt!!

snooby - 17-4-2014 at 12:13

What is an easy way to turn cobaltsulphate into the nitrate?

copperastic - 17-4-2014 at 12:23

It could be Nitropentaamminecobalt(III) chloride because that is purple.

Fantasma4500 - 17-4-2014 at 21:59

snooby: assuming im not performing wrong spoonfeeding.. i suggest turning it into the carbonate and then reacting the carbonate with nitric acid

sasan - 17-4-2014 at 22:34


Snooby do not use hydroxides to precipitate the cobalt hydroxide because it has some different hydroxides and oxides,and some of these would dissolve in the acids
I suggest you seriously using sodium hydrogen carbonate because it would make cobalt carbonate,if you use sodium or potassium carbonate then cobalt hydroxy carbonate forms(like copper hydroxy carbonate)

woelen - 17-4-2014 at 22:48

With cobalt(II) precipitates you should not go through high pH. At high pH, the cobalt(II) species (e.g. hydroxide, basic carbonate) are oxidized by air exceedingly easily and you end up with an impure mess of cobalt(II) and cobalt(III) species.

E.g. try adding some solution of NaOH to a solution of CoSO4.7H2O and swirl. Soon, you'll have a dark color near the surface of the liquid and on the solid material sticking to the glass. This is due to oxidation of cobalt(II) to cobalt(III) by oxygen from air.

Follow sasan's advice. Precipitate with bicarbonate and filter, rinse. Then dissolve in as little as possible nitric acid and allow to evaporate slowly in a warm and very dry spot. The nitrate unfortunately is quite hygroscopic so assure that the material can crystallize in a dry place.

snooby - 18-4-2014 at 05:19

The carbonate synth is probably the best option. Still i will just save my sulphate and buy some pure cobalt metal. Rather expensive stuff though. Reason for asking is because I want to try BNCP synthesis with the cobaltnitrate instead of the sulphate. Yields are very poor. Also check the results in the 5-ATZ deritaves topic plz:D