Sciencemadness Discussion Board

Metal oxides

Bedlasky - 28-5-2019 at 23:45

Hi.

I found on the internet e-shop with some pigments. And they sell MnO2, Cr2O3 and CoO wich intrigued me. I have problems with buy of Cr3+, Mn2+ and Co2+ salts because of stupid legislation. So my question is: Are these oxides well soluble in acids? Or they have bad solubility like Fe2O3? I have experience only with MnO2 - this is not a problem (MnO2 + oxalic acid or H2O2 in acidic media --> Mn2+ salt), but I haven't any experience with Cr2O3 or CoO. And have Cr2O3 good solubility in alkali metal hydroxides?

[Edited on 29-5-2019 by Bedlasky]

Ubya - 28-5-2019 at 23:56

some pottery oxides are fired at high temperature, causing a low reactivity, but yours could be unfired and dissolve easily

woelen - 28-5-2019 at 23:57

Cr2O3 is very inert. The only way to release the Cr(3+) ions is by dissolving it in molten NaOH or in molten KNO3, which oxidizes it to hexavalent chromium. Not the easiest and safest thing to do.

I doubt you can buy CoO. Most likely it is the black Co3O4 which you can buy. This stuff also is extremely inert. I have some of it and tried to dissolve it in conc. HCl to which some SO2 was added (made from metabisulfite and an acid), in order to reduce all Co to its +2 state. Again, this was a failure. After half an hour of near boiling the conc. HCl and having to withstand lots of fumes of HCl, I still only had a very pale blue solution. Maybe 0.1% or so dissolved. Useless stuff if you want to do aqueous chemistry of Co.

MnO2 is varying. I have two samples. One of them is a dark grey powder, which consists of many nicely glittering tiny crystals. Nice stuff to see, but totally inert towards even concentrated HCl. The other sample is a very fine black powder, and that material is quite reactive. It dissolves in conc. HCl and release Cl2. Unfortunatgely that sample is impure and contains quite a lot of iron (up to 5%) and this makes experimenting with Mn-salts more difficult.

Can't you buy MnCO3 and CoCO3 in shops for ceramics pigments? These chemicals both are quite pure usually and dissolve in acids with just a little heating.

TGSpecialist1 - 29-5-2019 at 00:27

You could also reduce the oxides with aluminium (or charcoal for Mn and Co) and dissolve the metals in acid. Good guides: https://www.youtube.com/user/DorcotBaconPhD

Bedlasky - 29-5-2019 at 00:37

I didn't find CoCO3 :(. Bud I find some auctions where they offer MnCl2, MnCO3, H3BO3, LiOH, ZrOCl2... Many chemicals :D. Do you know what with ZrOCl2? :D

Is this nickel sulfate or not? What do you mean? It is too blue, isn't it? Or not?

https://aukro.cz/siran-nikelnaty-1-5-kg-6948654918

Is good way to produce some Cr3+ and chromate from stainless steel?

woelen - 29-5-2019 at 04:11

The material you show in the aukro website really looks like nickel sulfate. Nickel sulfate has quite a strong and bright color.

ZrOCl2 is not a very interesting chemical. I have some, but all compounds of zirconium, which can go in solution, are colorless. Do not expect a colorful aqueous chemistry of this.

Isn't eBay an option for you (internationally), or can you only get materials from the Czech Republic? From eBay you can get many many different chemicals. Nickel salts, cobalt salts, copper salts, chrome alum or chromium sulfate, they are all there, also in the EU, so that shipping costs remain acceptable.

fusso - 29-5-2019 at 05:12

Quote: Originally posted by Bedlasky  
I have problems with buy of Cr3+, Mn2+ and Co2+ salts because of stupid legislation.
What stupid laws make such salts illegal, but not the parent oxide?

Bedlasky - 29-5-2019 at 06:09

Quote: Originally posted by fusso  
What stupid laws make such salts illegal, but not the parent oxide?


These chemicals isn't illegal. But they can only be bought in specialized stores. If you don't have chemical bussines they won't sell it to you.
Quote: Originally posted by woelen  
Isn't eBay an option for you (internationally), or can you only get materials from the Czech Republic? From eBay you can get many many different chemicals. Nickel salts, cobalt salts, copper salts, chrome alum or chromium sulfate, they are all there, also in the EU, so that shipping costs remain acceptable.


I've never tried it. How I pay there? Credit card, paypal?

woelen - 29-5-2019 at 06:59

For eBay it is most practical to have PayPal. It works very well and I think more than 50% of all my supplies are from eBay over the last 5 years.

DraconicAcid - 29-5-2019 at 07:20

Quote: Originally posted by Bedlasky  
I didn't find CoCO3 :(. Bud I find some auctions where they offer MnCl2, MnCO3, H3BO3, LiOH, ZrOCl2... Many chemicals :D. Do you know what with ZrOCl2? :D

Is this nickel sulfate or not? What do you mean? It is too blue, isn't it? Or not?

https://aukro.cz/siran-nikelnaty-1-5-kg-6948654918


No, that's exactly what nickel(II) sulphate hexahydrate looks like. It's not as green as the chloride.

fusso - 29-5-2019 at 07:30

Quote: Originally posted by DraconicAcid  
No, that's exactly what nickel(II) sulphate hexahydrate looks like. It's not as green as the chloride.
Is it as deep blue as CuSO4.5H2O?

Herr Haber - 29-5-2019 at 07:32

Quote: Originally posted by fusso  
Quote: Originally posted by Bedlasky  
I have problems with buy of Cr3+, Mn2+ and Co2+ salts because of stupid legislation.
What stupid laws make such salts illegal, but not the parent oxide?


Especially in the Cz republic !
I mean... you can literally buy tanks by the ton.

Bedlasky - 29-5-2019 at 07:41

Thank you all for your advice :)