CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Ferrous sulphate...unexpected precipitate
I added 56g of very fine iron filings to the beaker this morning. Added 200 mLs of 5.6 mole solution of Sulphuric acid. If the solution turns
reddish brown then I know more H2SO4 is needed, because I need to keep it in the ferrous stage.
Looking at the solution after almost 3 hours it seems a bit unexpected. There is a huge grey precipitate on the bottom of the beaker that is at least
10 times the mass of the 56g Iron filings. It has a sand-like consistency a bit muddy, but is grey. The solution of liquid on top of this is
completely black. There is no sign of the expected light green ferrous sulphate crystal, the whole solution is divided between the grey sand like
consistency and the black liquid on top.
Does anybody recognise what is wrong please, I could not imagine that there would be any difficulty in such a simple reaction.
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
Mixell
Hazard to Others
Posts: 449
Registered: 27-12-2010
Member Is Offline
Mood: No Mood
|
|
Was the iron pure? The black water sounds like a suspension of carbon particles , and the grey stuff might be a suspension of silicon (or
oxides/hydrated oxides of it).
You sure it is 10 times the *mass* and not the *volume* of the iron fillings?
If the grey precipitate is just voluminous and not dense, then your iron might be of the following type of alloy:
http://en.wikipedia.org/wiki/Pig_iron
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Hi Mixell, the iron is fine iron filings bought from a chemical supplier. The iron filings filled about a centimetre up the beaker and the present
precipitate of grey matter fills about 4 inches up the side of the beaker, The black solution I imagined might be carbon, but the iron filings can't
be pig iron surely?
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
Mixell
Hazard to Others
Posts: 449
Registered: 27-12-2010
Member Is Offline
Mood: No Mood
|
|
Not necessarily pig iron, but it might be something similar...
Anyway, the grey stuff is probably silicon.
That's my best guess based on your description.
|
|
|
IrC
International Hazard
Posts: 2710
Registered: 7-3-2005
Location: Eureka
Member Is Offline
Mood: Discovering
|
|
Does anyone see a trend here? Look at the Iron Chloride thread, bought from a chemical supplier. All my years we trusted chemicals from such sources
were pure and as labeled. If I assume most if not all our well known suppliers are likely getting all their chemicals from manufacturers in China now,
it leads one to conclude we can no longer trust the labels on our reagents. Probably China is all they have for suppliers of many chemicals today so
they have no choice left but stocking items made there. I have seen so many examples of impurities in something which should be at least be close to
what is advertised, all made in China. Example a roll of speaker wire I just bought, made in China. Wanting to solder terminals I tried in vain to
scrape and flow flux in an effort to get rid of the oxygen which was so bad the copper, each strand, was dark black inside the insulation cover. Did
not matter how many feet down the roll, every strand in the entire roll was impossible to solder from the large amount of oxygen in the metal. This is
not new, I have been seeing this ever increasingly in the last decade. We all would assume if CHRIS25 bought a bottle of lab quality Iron filings from
a reputable supplier such a large amount of Silicon (nor Carbon) should not be in it right? I wonder when someone will have a life threatening
disaster during an experiment from chemicals in their reactions which they were not expecting and which should not have been there. We can't even
trust Taco Bell anymore is it dead cow or horse in our burritos, or in our burgers from other fast food chains? I guess none of this should be
surprising anymore.
Where was the acid manufactured? At this point we could be dealing with multiple impurities in several of our starting materials.
[Edited on 3-2-2013 by IrC]
"Science is the belief in the ignorance of the experts" Richard Feynman
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
As I have read, all iron has silicon and carbon in it, but it has not affected the Iron based reactions I did in the past. The amount of silicon is
up to 6%. So 6% of 63g is hardly going to affect the reaction is it? Especially since I have used rusty barbed wire as a source of iron in a few
reactions in the past.
So basically these iron filings are no good for anything chemistry except demonstrating magnetic fields!
[Edited on 2-3-2013 by CHRIS25]
[Edited on 2-3-2013 by CHRIS25]
[Edited on 2-3-2013 by CHRIS25]
It could be that my stoichemetry is off? I was filtering the solution and noticed a subtle light green solution collecting in the beaker. I decided
to add sulphuric acid to some of the black grey precipitate that was left in the other beaker and it reacted. My immediate thought was that the
sulphuric acid was not 17.6mol, ie not concentrated as was sold to me by a farmers business, although they are reliable as a rule. I mixed everything
back into its original beaker and added conc. sulphuric acid, about 75mLs. It is reacting quite strongly.
Anyway the original calculations based on my sulphuric acid were:
56g Fe + 65mLs H2SO4 in 200 mLs water to make 5.6mol
(54 mLs/1 liter = 1mol; therefore 54 x 5.6mol = 302; 302/5 = 60 mLs acid in 200 mLs water. Theoretically should have worked.
Acid based on 98.079/1.84 = 53.3 mLs
The addition of acid results in an immediate change from black solution to grey/white colour solution with what I imagine to be unreacted Iron
filings still at the bottom of beaker. This all obviously means that the sulphuric acid was not concentrated to begin with, in other words not enough
acid added.
I know you can acquire ferrous sulphate through copper sulphate but I have so much iron and sulphuric acid.
[Edited on 2-3-2013 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
vmelkon
National Hazard
Posts: 669
Registered: 25-11-2011
Location: Canada
Member Is Offline
Mood: autoerotic asphyxiation
|
|
Isn't all iron produced by reduction with carbon at high temperature? They all tend to be impure. The cleanest source is probably white iron, for the
home chemist. Get it from transformer cores.
I have read that high purity iron is very soft, softer than aluminum.
|
|
|
plante1999
International Hazard
Posts: 1936
Registered: 27-12-2010
Member Is Offline
Mood: Mad as a hatter
|
|
I would highly doubt it, I have some experience with metals. Copper can be quite strong, much like tempered iron. One day I had heated for a long time
a 1/16 aluminium sheet at 400-500 for few hour, and then cooled slowly. The sheet was so soft it was unbelievable. It was softer than cardboard! When
you buy aluminium it is already tempered, probably 3/4 tempered.
[Edited on 2-3-2013 by plante1999]
I never asked for this.
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Well it seems that the iron filings did work, and the irony here is that I used the same stoichemetry but used cast iron bits (1cm cbic) which I cut
up. Using thses pieces today results in a thoroughly brown solution. this I presume is the Fe3+ the ferric. I added more and more conc. sulphuric
to the solution to keep the iron pieces reacting but each time they just stopped after about 5 mins; and I am left with a beaker full of brown
solution. However after filtering a ton of grey/white sand-like consistency mass, from the original reaction, into the filter the solution that
dropped down was a beautiful green and medium large ferrous sulphate crystals started to precipitate out - I re-dissolved them by adding some more
sulphuric acid and am now heating the solution to extract half its volume (about 600mLs) and will then evaporate to the heptahydrate.
So whatever that huge mass was I do not know at all, but I have ferrous sulphate, as for the cast iron chunks, well that did not work at all. So many
of these sites that talk about iron and sulphuric acid really need to get it accurate and highlight what type of iron, certainly not cast iron,
although I am aware that one could add nitric acid to ferric sulphate solution to get the ferrous. Even adding concentrated sulphuric acid to a
concentrated ferrous sulphate will give me monohydrate, although I do not know exactly how concentrated the ferrous sulphate needs to be.
[Edited on 2-3-2013 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
12AX7
Post Harlot
Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline
Mood: informative
|
|
As I recall, I got a brownish suspension (not solution) from dissolving assorted steel in acid. The color is not due to Fe(III), which would react
instantly with any remaining metal.
Incidentally, the precipitate is related to many compounds (including combinations of FeS, Fe3P and various compounds with each other and carbon)
which are responsible for the flatulent odor which accompanies the dissolution of metals.
After all the metal has dissolved, allow the solution to settle and decant. Or use a very fine filter.
Evaporate the solution (you'll probably have syrupy sulfuric acid leftover) and crystallize. Wash, pat dry over paper towels, then dissolve in clean
water, evaporate and recrystallize.
After recrytallization, it should be, I would guess, 95% or better FeSO4.7H2O, with a little green-yellowishness due to a minor amount of Fe(III).
If the recrystallization solution is left to sit for a long time, there may be a very fine yellowish precipitate, which is probably something like
ferric hydroxide. In the absence of metal, it will slowly oxidize in air.
Tim
[Edited on 3-2-2013 by 12AX7]
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Pale Green Flat Slabs concealing a white creamy solution all sitting at the bottom of 600mLs of light green ferrous sulphate solution, while at the
same time the expected tiny ferrous sulphate crystals are floating on top of tje solution.. The creamy solution was well hidden and protected from
the ferrous sulphate solution above. Iron and Sulphuric acid, nothing else, but have no idea what this is anymore or why it happened.
"I tipped out the solution through a filter and was left with a hard crust which is actually a very pale green, I pierced the crust with a plastic
spoon easily and to my surprise there was a white creamy liquid underneath. The green solution which is now very dark green has crystals forming at
the bottom, very small ones, tiny. The crust is now broken up into quite large slabs, not crystals, slabs about 1 cm square really, they are at this
moment in the creamy white liquid and do not dissolve back into it".
These pale green slabs are the same colour as Melanterite
[Edited on 4-3-2013 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
ScienceSquirrel
International Hazard
Posts: 1863
Registered: 18-6-2008
Location: Brittany
Member Is Offline
Mood: Dogs are pets but cats are little furry humans with four feet and self determination! 
|
|
The grey solid is almost certainly ferrous sulphate as the monohydrate.
You need a lot of water present and you have to keep it cool to get the heptahydrate.
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
I don't see how to be honest. It broke up into slabs and was hiding a creamy white fluid. When I tried to wash the white fluid away from the slabs
it just kept clinging there and the slabs just kept getting re-dissolved. So I 'm lost. I have just made a successful batch of ferrous sulphate
heptahydrate using steel wool instead of iron filings. Will do the same ting again, and also will re-do the iron filings reaction once more. The
only difference between the two reactions, (iron filings versus steel wool) was the amount of sulphuric acid. The iron filings had a far more
concentrated amount of the acid. Stoichemetry had to be thrown out of the window here because The mass of iron in steel wool seems to be less than
it's weight, Sulphuric acid needs to be very dilute to keep the iron in the ferrous state, and maybe the higher concentration in the iron filings did
turn it into a mixture of ferrous and ferric, although there was certainly no brown, UNTIL that is when I washed the beakers: When rinsing with water
to clear out the white creamy mysterious fluid the water was a normal clarity after the cream white dissappeared, and then suddenly after filling the
beaker with more clear tap water the tap water turned light brown, this happened to all three beakers that had been contaminated with this white
creamy fluid, (now known as WCF), So all three beakers followed this same order: washed, WCF gone, more tap water, water turned light brown.
Obviously some residue stuck to the sides of the beaker. In the same manner this same residue must have been stuck to the precipitate from the iron
filings reaction because it would not wash away from the light green slabs.
Good news: Have made the heptahydrate; will be repeating this experiment with iron filings and steel wool once more.
Question? Can I wash the iron filings in anything or will a simple flush with distilled water clear out any 'unwelcome participants'? I did not wash
the iron filings before the first reaction took place.
[Edited on 5-3-2013 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
Vargouille
Hazard to Others
Posts: 380
Registered: 16-4-2012
Member Is Offline
Mood: No Mood
|
|
The brown color could be a combination of oxidation of residual ferrous ions by solvated oxygen and the resulting hydrolysis of the ferric ion to a
brown precipitate. As for the wash, it depends on what the unwelcome participants are. If the contaminants are grease or the like, an acetone bath
would clean it right up, but if they are silicates, then a water wash won't remove much. The simpler route in the latter case would be to run the
reaction and filter off whatever doesn't react before isolating your product.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
