Sciencemadness Discussion Board - Ferric oxide (Fe2O3) that doesn't react with HCl?

Ferric oxide (Fe2O3) that doesn't react with HCl?

DrMario - 30-10-2014 at 14:28

I bought online some ferric oxide - at least that's what I thought I bought. It arrived as a very fine orange-red powder. First thing I tried was reacting it with diluted phosphoric acid. No reactin. None whatsoever. The fine powder stays as a suspension in water and does not show any signs of change with addition of H3PO4. So then I took another sample, suspended it in water and added concentrated HCl. NO REACTION!?? What is this bull###t?

By the way, it doesn't show any signs of being ferromagnetic. I have some very powerful magnets at home, and this powder doesn't show even the smallest attraction force.

DrMario - 30-10-2014 at 14:29

Just for fun I made some aqua regia. You guessed it: no reaction at all. I have a glass bottle with aqua regia and this mistery powder suspended in it.

Amos - 30-10-2014 at 15:58

Homemade rust that I made both by electrolysis and plain old exposure of iron wool behaved the same way. Maybe certain forms or polymorphs or whatever are similar to titanium dioxide, most grades of which won't react with pretty much anything.

DrMario - 30-10-2014 at 16:13

Quote: Originally posted by No Tears Only Dreams Now

Homemade rust that I made both by electrolysis and plain old exposure of iron wool behaved the same way. Maybe certain forms or polymorphs or whatever are similar to titanium dioxide, most grades of which won't react with pretty much anything.

Difference being that titanium oxide is notorious for being unreactive/inert, while Fe2O3 is notorious for being easily attacked even by weak acids.

BUT... what you're telling me is quite intriguing. So, your electrolysis Fe2O3 is unreactive? Hmmm.... What are the magnetic properties of your "red" iron oxide?

Brain&Force - 30-10-2014 at 16:18

I have a good feeling the oxide was calcined enough to render it inert.

HgDinis25 - 30-10-2014 at 17:19

Try fusing it with KOH (NaOH can also be used) and test for the presence of a pink solution (ferrate ions). Even calcinated Iron(III) Oxide oxidizes to ferrate under these conditions.

Texium - 30-10-2014 at 20:10

The only ferric oxide that I've dealt with in a chemistry setting was freshly precipitated stuff from oxidized ferrous solutions. In that form, it's yellowish brown (it's used as the pigment ochre) and reacts readily with acids. I used conc. HCl to clean it from my frit funnel with no issues at all. I know I've read somewhere before* that non-hydrated "red" ferric oxide is much less reactive than the hydrated "yellow" kind.

*It's late here and I don't want to spend time searching for the source right now

DrMario - 30-10-2014 at 23:30

Quote: Originally posted by HgDinis25

Try fusing it with KOH (NaOH can also be used) and test for the presence of a pink solution (ferrate ions). Even calcinated Iron(III) Oxide oxidizes to ferrate under these conditions.

Okay, but I'll have to write off that test tube, I presume? I wish I had a ceramic pot.

Texium - 31-10-2014 at 04:18

If you can find stainless steel condiment cups somewhere, those make great stainless steel crucibles and are quite cheap compared to real ones. I successfully fused MnO2 and KOH in one to make manganate, and this reaction would be analogous to that one.

blogfast25 - 31-10-2014 at 05:32

Quote: Originally posted by DrMario

Nope, not at all.

MOST oxides, if calcined hard for long enough become unresponsive to acids: weak, strong, dilute or concentrated. Mine [Fe2O3] doesn't respond to either hot HCl 37 % or boiling 98 % H2SO4. I have ZnO that behaves the same way.

Aqua Regia here is a waste of nitric acid. AR only works when it has something to oxidise, like gold or other PGMs.

As someone suggested, try fusion with NaOH or KOH.

Also fusion with NaHSO4 (sodium bisulphate) should work. Molten bisulphate is much less aggressive to glass than NaOH/KOH, I've done this in conical flasks w/o damage.

Once you've dissolved the material, you can then re-precipitate it, wash it and dry it. The 'fresh' iron oxide will respond to acids much better.

[Edited on 31-10-2014 by blogfast25]

Morgan - 31-10-2014 at 06:23

Maybe you could try strongly heating the Fe2O3 to see if you can get it to respond to a strong magnet or if it changes color. Sometimes heating will change the spacing. I found some monel screws developed a somewhat stronger pull after heating and then cooling them back down to room temperature for a test. A few months ago I was curious just how much attraction a 1 pound bottle of powdered red iron oxide would pull towards an N52 magnet. I was more of an attraction that I thought it would be.
There is a type of invar consisting of 25% nickel that can be non-magnetic at room temperature but upon cooling with dry ice it becomes and remains ferromagnetic up to 580 C.

DrMario - 31-10-2014 at 09:46

Quote: Originally posted by blogfast25

Quote: Originally posted by DrMario

I feel I should explain something: I tried aqua regia at the point where I didn't anymore know what this powder was - and for a moment thought it may be HgS (cinnabar) due to the colour. I do happen to know how aqua regia works, though I'm no expert.

DrMario - 31-10-2014 at 09:49

Quote: Originally posted by zts16

If you can find stainless steel condiment cups somewhere, those make great stainless steel crucibles and are quite cheap compared to real ones. I successfully fused MnO2 and KOH in one to make manganate, and this reaction would be analogous to that one.

That is a good idea. Sadly, I don't have any, but I'll look for some other disposable stainless steel vessel.

Was your permanganate significantly contaminated by the stainless steel - with iron, nickel or chromium?

DrMario - 31-10-2014 at 09:53

Quote: Originally posted by Morgan

Maybe you could try strongly heating the Fe2O3 to see if you can get it to respond to a strong magnet or if it changes color. Sometimes heating will change the spacing. I found some monel screws developed a somewhat stronger pull after heating and then cooling them back down to room temperature for a test. A few months ago I was curious just how much attraction a 1 pound bottle of powdered red iron oxide would pull towards an N52 magnet. I was more of an attraction that I thought it would be.
There is a type of invar consisting of 25% nickel that can be non-magnetic at room temperature but upon cooling with dry ice it becomes and remains ferromagnetic up to 580 C.

Just a quick reply for now: I did heat the powder to a bright orange incandescence with my gas torch. No change in colour at all. Also, no ferromagnetism as far as I could notice.

blogfast25 - 31-10-2014 at 11:04

While disposable steel cups can be great, NaOH/KOH melts will leach also chromium from SS steel (direct experience).

Try a small scale test with sodium bisulphate in a (glass) test tube. Use 2 to 4 times the stoichiometric requirement of bisulphate, grind the mixture down to fine and heat on medium/high Bunsen for 1/2 hour. Leach with hot deionised water. Filter off any residue.

[Edited on 31-10-2014 by blogfast25]

Morgan - 31-10-2014 at 15:50

Could you post a photo to show the tone or color of your oxide? It's an interesting riddle as to what's going on.

Texium - 31-10-2014 at 21:01

Quote: Originally posted by blogfast25

While disposable steel cups can be great, NaOH/KOH melts will leach also chromium from SS steel (direct experience).

Oh, I wasn't aware of that. I guess it would be pretty difficult for me to tell anyway by looking at it, since the Cr(III) color would blend right in with the Mn(VI) (which was what I was making, not Mn(VII))
Would investing in a small nickel crucible possibly be a good idea? They don't seem to be too overly expensive.

Morgan - 1-11-2014 at 05:34

I bought these Alfa Aesar nickel crucibles a few weeks ago. As nickel is only ~7 dollars a pound, it seems like you could make your own if you had some small sheets of nickel with a little work.
http://www.ebay.com/itm/Three-3-High-form-30mL-nickel-crucib...

blogfast25 - 1-11-2014 at 05:47

Quote: Originally posted by Morgan

Could you post a photo to show the tone or color of your oxide? It's an interesting riddle as to what's going on.

If I find time I will but I already know from the OP’s description that mine is much darker: dark brown with a reddish tint. Ferric oxides do come in various colours: from ochre to almost black. Not sure what that is all about.

Quote: Originally posted by zts16

Would investing in a small nickel crucible possibly be a good idea?

Yes, yes, yes and yes again! They resist both the strongest alkali and acids (the latter within reason), are much easier to clean and virtually indestructible (but MP is much lower than ceramic, of course). You can bounce them off the floor! Take sand paper to them to restore to bear metal!

I started selling them a while back and remain a bit surprised by the slow take up.

Morgan - 1-11-2014 at 08:03

I remember when I was about 10 years old digging some soft malleable clay from some cliffs and the clay had multi-colored patches all very close to each other separated by only inches or a foot or so in some cases. The colors were yellow, orange, and red and a pleasing muddy purple here and there. I wonder if it was iron that caused all the variations?

Yellow ochre, FeO(OH)·nH2O, is a hydrated iron hydroxide (limonite) also called gold ochre
Red ochre, Fe2O3, takes its reddish color from the mineral hematite, which is an anhydrous iron oxide.
Purple ochre, is identical to red ochre chemically but of a different hue caused by different light diffraction properties associated with a greater average particle size.
Brown ochre (goethite), is a partly hydrated iron oxide.
http://en.wikipedia.org/wiki/Ochre