condennnsa
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iron sulfate please help
I took 500g of 30-35% H2SO4 , and added 146 g iron nails, the reaction was slow at start, I applied heat to get it to react vigorously. While heating
the flask was always covered by watchplate. While heating I also kept adding water to make sure the iron sulfate produced dissolved to keep the
reaction going.
After about 4 hours of heating, the iron nails stopped producing hydrogen gas, and the solution started to boil, indicating the reaction was at
completion. I cooled the liquid and filtered it, resulting in a beautiful green solution. At the bottom of the flask i was left with 35 grams of
unreacted iron nails, so 111 g of iron went in solution.
Now the problem with this iron sulfate solution is that everytime i try to heat it to boil off the water and concentrate the solution, the iron
sulfate seems to be decomposing , producing small amounts of red precipitate which i think is fe2o3.
i found this on wikipedia :
"Upon exposure to air, it oxidizes to form a corrosive brown-yellow coating of basic ferric sulfate, which is an adduct of ferric oxide and ferric
sulfate:
12 FeSO4 + 3 O2 → 4 Fe2(SO4)3 + 2 Fe2O3"
but i can't imagine where the o2 could have come from...
is feso4 always so unstable? what would be the best way to get those nice blue-green heptahydrate crystals without decomposition?
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Paddywhacker
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Yes, FeSO4 will be oxidized by atmospheric oxygen. You may be able to minimize that by leaving the nails in the mixture as you concentrate and
crystallize it.
Ferrous ammonium sulfate, made by dividing your H2SO4 in half, reacting one half with iron and neutralizing the other half with ammonia, then mixing
and crystallizing, is more air-stable.
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entropy51
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In my opinion, the easiest way to make FeSO4 is to dissolve iron (steel wool works well) in a saturated solution of CuSO4 containing a few drops of
H2SO4. When excess iron remains and the blue color has disappeared, filter off the undissolved iron and the Cu flakes. Let the solution stand for a
long time (weeks) and nice green crystals of FeSO4 will form. You can't rush it. If you're patient you can make quite a lot of FeSO4 this way.
There are a couple of good pages on the web that describe in detail how to make good FeSO4 by dissolving Fe in H2SO4, but I prefer the CuSO4 method.
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Magpie
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Not as elegant as the procedure of entropy51, but here's some more methods:
http://www.sciencemadness.org/talk/viewthread.php?tid=5529&a...
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condennnsa
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So what paddywhacker is saying is that it is possible if some Fe2(SO4)3 might have formed, it could react with metallic iron back to FeSO4? that would
be great!
but what about the Fe2O3 that formed from the initial reaction? I considered adding H2SO4 dropwise to the cold solution, to make it very slightly
acidic, preventing the fe2o3 from existing. would the H2SO4 prefer to attack the Fe2O3 rather than metallic iron?
i will filter it again, add a few nails, and concentrate it and see... thanks!
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condennnsa
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Well, thanks so much everyone.
I took my Fe2O3 contaminated liquid, brought it to a boil to dissolve all the feso4 crystals, added 2 more nails (about 9.5g), and an additional 10ml
30%H2SO4 . as soon as the acid entered the solution all the fe2o3 particles magically disappeared! I continued to boil the solution covered until the
nails stopped producing H2 gas, filtered it (very little filter cake, a pinch of carbon, no red Fe2O3) .
Put it in a crystallizing dish(the nails also!,like paddywhacker suggested), boiled it to about 500ml, and now its under a fan, there are already
plenty of beautiful green crystals, no sign of impurities visible.
I now think that atmospheric oxygen was not the culprit of my decomposition, but rather that i used unboiled cold tap water to replenish water levels.
I didn't know that water can actually dissolve so much oxygen!
thanks!
[Edited on 25-7-2010 by condennnsa]
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