Sciencemadness Discussion Board

Iron oxide, sulphuric acid and water

brew - 12-5-2008 at 22:21

Hi all,

I am experimenting with different reactions and decided to make pure iron via electrolyis and achieved this and was interupted (4 hours)as I was filtering and returned to an oxidised iron. For some reason I decided to add H2SO4 98% to this dried iron oxide and some 1 hour later discovered a whitish grey precipitate at the bottom of the flask. I assumed this to be iron sulphate. For another curious exploration I decided to add H20 and did so very cautiously drop by drop. The reaction was exothermic and produced a gas that was not so pleasant (sulphur dioxide ??)hence wore my special mask ect. What occured next was that the bottom layer of whitish/grey precipitate remained followed by a middle layer of a chalky appearance, with the top layer being a green somewhat oily appearance and with gloves a single drop appeared to be that of an oil. Having a limited chem knowledge. I am not sure exactly what has happened here. I am learning about ox/red reactions and would be interested in anyone perhaps helping me understand what has occured. Perhaps this is basic chem hence the inclusion in Beginnings.:)

ShadowWarrior4444 - 12-5-2008 at 23:02

I too have encountered this paste-like substance when running experiments involving steel and dilute sulfuric acid. Iron Sulfate should be green soluble crystals, so it would not be that. I can tell you that when I heated the paste-like substance with a propane torch it appeared to rapidly turn red, indicative of iron oxide formation, with no gas evolution apparent. This leads me to believe that it is finely divided iron, though I am not entirely sure.

For me, it was formed when dissolving steel in 30% H2SO4--first the green crystals of iron sulfate formed, then over time this paste began to appear around the metal, adding more metal resulted in the formation of more paste. (This testing was carried out over quite some time.)

A word on scents: SO2 smells of gunpowder, (rather it is the other way around.) H2S smells of rotting eggs, and it detectable by humans at .0047 ppm if I recall.

As for colors, Iron Hydroxide should be brown, oxide can be red, yellow or black (red is most common), sulfate is most definitely green (aka green vitriol,) FeS should be yellowish. (Pyerite color.)

[Edited on 5-13-2008 by ShadowWarrior4444]

brew - 13-5-2008 at 00:49

It smelt more like gunpowder and not rotting eggs. It makes more scence to be SO2 rather than hydrogen sulphide. The paste is interesting. I will repeat what I did and explore this further. If it was the iron hydroxide and if I added sulfuric acid the result should still be the greenish colored metal salt of sulphate? and not the white/grey precipitate that I observed. Perhaps it was this paste that had also coated the metal.I will repeat what I did and try to learn from these reactions. Thanks for your input. As I am learning and relatively a newbie as such other than lab skills in the basics etc. What is the best way to store pure iron? is it in an oil that prevents O2 from penetrating etc or just in a sealed air tight container or does one need to evacuate the said container. I suppose I should experiment and find out rather than ask. I tell you having the theory may be useful but doing this stuff is a new ball game. Thanks again

YT2095 - 13-5-2008 at 01:04

it Could be anhydrous iron sulphate, that is a whiteish powder, you did use 98% acid after all!

edited to add: it`s also worth mentioning that the Green color of the crystals is only very mild, it`s nothing like Nickel salts for instance, and in soln you need quite a bit of it to see it as green.


[Edited on 13-5-2008 by YT2095]

ShadowWarrior4444 - 13-5-2008 at 01:14

Quote:
Originally posted by brew
It smelt more like gunpowder and not rotting eggs. It makes more scence to be SO2 rather than hydrogen sulphide. The paste is interesting. I will repeat what I did and explore this further. If it was the iron hydroxide and if I added sulfuric acid the result should still be the greenish colored metal salt of sulphate? and not the white/grey precipitate that I observed. Perhaps it was this paste that had also coated the metal.I will repeat what I did and try to learn from these reactions. Thanks for your input. As I am learning and relatively a newbie as such other than lab skills in the basics etc. What is the best way to store pure iron? is it in an oil that prevents O2 from penetrating etc or just in a sealed air tight container or does one need to evacuate the said container. I suppose I should experiment and find out rather than ask. I tell you having the theory may be useful but doing this stuff is a new ball game. Thanks again


Asking is of as much value as experimenting on your own, and much less time consuming. A conjunction of both will yield very favorable results for the intrepid scientist. Added to that, a bit of thoughtful Googling, and perhaps a slight bit of Wiki, and your progress will go very smoothly indeed.

Googling Inorganic Qualitative Analysis, or inorganic assaying may help you determine the composition of chemicals, as will searching for a suspected chemical's name and examining its properties.

To paraphrase an industrial revolution treatise: 'Read the scientific works of others, for in them are many years of research... and it will likely save you *alot* of time.'

As for storing things away from water/air, mineral oil is quite useful. Great for keeping high-voltage equipment from annoying you as well. It's also conveniently found in the laxative section of your nearby pharmacy, along with several nice magnesium compounds. Do not be deterred by quizzical glares.

As an aside, I personally like grinding up a metal such as iron with a tungsten carbide cutter when I need a quantity of powder.

12AX7 - 13-5-2008 at 10:03

Adding drops of water to concentrated H2SO4 will produce boiling and spitting, the exact hazard why you are instead supposed to add acid to water. The fumes you detected are one of the hazards associated with this (adding more water and getting an eruption of boiling acid is the other hazard!).

White paste, definitely iron sulfate. Dissolves slowly, doesn't it? Most anhydrous sulfates do anyway. What does dissolve will turn green when dissolved in water, and especially when exposed to air, so that some Fe(II) is oxidized to Fe(III), which has a stronger color.

The best way to store pure iron is melted into a bar (think mild steel, 98% pure iron) and lightly greased, kept away from acid fumes, salt spray and moisture.

Tim

Klute - 13-5-2008 at 12:09

FeSO4.H2O forms above ~80°C IIRC, and there are over hydrates that forms under this temperature. Considering the dessicating conditions (conc. H2SO4 and further heating bya dding H2O to the acid, it surely formed.
When i wanted to make some myself, I tried slowly evaporating on a hot plate the green solution obtained by dissolving Fe wool in dilute H2SO4, and obtained a whiteish solid, sparingly soluble in water. When this was done at RT or slightly warm temperature, beautifull green prisms were obtained.

When left in a dryish atmosphere, these dehydrate to the mono hydrate eventually. The oxydation to Fe III is inhibited by traces of sulfuric acid, so no need to wash/recrysatllize excessively. Ethanol works nicely for washing.

brew - 13-5-2008 at 15:49

Thankyou all,

I am aware of the usuall adding of acid to water but broke the rules as firstly it was small scale and I did it very gradualy and perhaps still not the thing to do!- but thankyou for pointing this out as it should be pointed out etc.
I have just checked the flask and it still remains layered as initialy described. If this white paste like substance is anhydrous metal sulphate I will remove the top green layer solution and add water to the paste and see if indeed it turns the water a greenish tinge - hence as stated the Fe(ll) turning to Fe(lll).
As far as the not so pleasant fumes I smelt when I did add water drop wise to conc H2S04 and Fe(?). The acid/ water reaction I think would only produce steam?? which is not unpleasant so I am not sure what I actualy smelt. I will repeat what I did- CAUTIOUSLY - and observe more. I will also dissolve Fe wool in dilute sulphuric and explore by means of evaporating in order to obtain various crystals. The room temp ones sound really cool.
I will check out the mineral oil and look out for the other magnesium products allthough I have 250 g of turnings to play around with and can cheaply access more. As far as the quizzical stares go and I do get them. If it feels as if I am getting negatively sussed out by the shopkeeper etc I just reach in to my wallet and show them my Uni card and tell them the truth. I am doing a science degree at Uni etc and doing some home projects. It is the truth and because it is the truth I am totaly relaxed about it. With this being said I am also very much aware that having chem reagants and glassware is all but a step away in the LEO's eyes that I am doing something wrong. I need to be mindful and not to relaxed and I have been telling myself for over a month now that I need to have a book that lists the chem I have and also lists the experiments/objectives etc so I cant be caught out on a some kind of intent charge. All that they need is some past history of being perhaps a little wild and happy hungry! and stuped in the process etc and from that they paint a picture that would totaly fuck you up. I have also discussed what I am doing with friends and mentioned this issue as a back up in case this scenario ever plays out.This might not be enough but it might help. I feel one has to be this careful in these times.
And thankyou 12AX7 for the link it looks interesting and good to learn the basics.

brew - 13-5-2008 at 17:37

I just separated the top greenish colored solution from the white precipitate and added H2O and as explained this too slowly turned a shade of green.
By the way That chemistry section 12AX7 is quite good. Is it your site?
I am also exploring the oxidation of toluene with Pot'permangenate and have no set data and thought it would be interesting to go about this from scratch. It may be the slow way but it is kind of fun to look at questions such as what solvent I should add the KMnO4 too and explore reaction conditions and amounts. I think I can know if oxidation has occured by the mangenate being reduced, hence color change from purple to something. I can also separate and add NaOH to hopefully form I think is called sodium benzoate. As adviced it is perhaps conveniant and common scence to ask questions but sometimes the fun is finding out yourself. I am not sure if my toulene oxidation is one of them but I will find out.

12AX7 - 13-5-2008 at 21:17

Quote:
Originally posted by brew
As far as the not so pleasant fumes I smelt when I did add water drop wise to conc H2S04 and Fe(?). The acid/ water reaction I think would only produce steam?? which is not unpleasant so I am not sure what I actualy smelt.


Ah, but the steam and splatter makes an aerosol of nastiness. I've found NaOH does this too (it gets hot when dissolved in water, though not as hot as H2SO4). NaOH aerosol is worse, as the body has less ability to neutralize base than acid (hence why one should always wear goggles when handling NaOH, and I mean moreso than generally wearing goggles in the lab ( which one should do anyway :) )).
Quote:

By the way That chemistry section 12AX7 is quite good. Is it your site?


You mean in my sig? Yes, that is my site. Thanks!

Tim

brew - 13-5-2008 at 23:43

To ShadowWarrior444,

I have decided to try my hand at converting toluene to benzoic acid and I dare say a degree of benzaldehyde. I will accept your advice and look up how others have achieved this but do so in order to understand how their reagants/catalysts used brought about such a change. From that I may consider, if I end up understanding the mechanism of the reaction, experimenting with reagants at hand. It is obvious that to attempt chem from scratch may be exciting but perhaps somewhat neurotic and time wasting. I will try to be balanced. There is also the obvious limitation of reagants which calls for experimentation to begin with.

bmc