TheNaKLaB
Hazard to Self
Posts: 51
Registered: 18-9-2011
Location: Australia
Member Is Offline
Mood: Elastic
|
|
Electrolysis to make Iron (II) Hydroxide then Iron (III)Oxide?
Hey ScienceMadness,
I am soon to be uploading a video on making Red Iron Oxide (The complete guide) through electrolysis. I've always wondered what actually is happening
in this reaction and it would be greatly appreciated if someone could help me work this out.
I made a solution of about 5 grams of Sodium Chloride salt dissolved in 500 mL of water in a beaker. I then added an Iron electrode connected to
positive and a stainless steel rod connected to the negative. I used a 12 volt DC power supply and electolysed the solution for about 3 hours. After
that time, I removed the electrodes and mixed the solution. There was a thick black (slightly green) mass at the bottom of the beaker.
Would this black/green mass be Iron (II) Hydroxide? Fe(OH)2
I then filtered the solution to obtain the black/green mass. I then heated it in the beaker with my bunsen until the black/green mass started to dry
and all of it turned red. The red compound was a powder and it is ferromagnetic.
Would this red compound be Iron (III) Oxide? Fe2O3
So if the black/green mass is Iron (II) hydroxide, does it oxidize upon heating to Iron (III) Oxide? That seems to look like what happened during this
reaction.
Thankyou for your time!
[Edited on 19-09-2011 by TheNaKLaB]
|
|
|
LanthanumK
Hazard to Others
Posts: 298
Registered: 20-5-2011
Location: New Jersey
Member Is Offline
Mood: No Mood
|
|
Yes. Mere exposure to air can complete that reaction as well, though not as quickly.
hibernating...
|
|
|
TheNaKLaB
Hazard to Self
Posts: 51
Registered: 18-9-2011
Location: Australia
Member Is Offline
Mood: Elastic
|
|
Ok thanks! So just by heating the Iron (II) Hydroxide in Oxygen oxidizes it to Iron (III) Oxide?
|
|
|
AJKOER
Radically Dubious
Posts: 3026
Registered: 7-5-2011
Member Is Offline
Mood: No Mood
|
|
FYI, Iron readily dissolves in HOCl forming a Ferric salt. Add NH4OH and you will have Fe(OH)3. Dehydrate to obtain Fe2O3, but note that for most
aqueous chemical reactions, the fresh precipitate of Fe(OH)3 may be better (more chemically reactive).
One way to prepare a dilute, but still reactive solution of HOCl (with a presence of Sodium acetate), is by mixing Bleach (NaOCl) and vinegar.
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
Quote: Originally posted by AJKOER  | FYI, Iron readily dissolves in HOCl forming a Ferric salt. Add NH4OH and you will have Fe(OH)3. Dehydrate to obtain Fe2O3, but note that for most
aqueous chemical reactions, the fresh precipitate of Fe(OH)3 may be better (more chemically reactive).
One way to prepare a dilute, but still reactive solution of HOCl (with a presence of Sodium acetate), is by mixing Bleach (NaOCl) and vinegar.
|
Commercial bleach solutions only contain 4 - 5 % sodium hypochorite. In acid conditions hypochlorite is quite unstable. Basically your iron would
dissolve into weak, dilute acid, quite slowly, to Fe (II), then get oxidised immediately by the Cl (I) to Fe (III). But since as there isn't much ClO-
to begin with that oxidation reaction stops fairly soon. If your bleach/vinegar mixture was 50/50 it would be about 0.4 M in acetic acid and 2 - 3 %
hypochlorite, so go figure!
This is another one of these reactions you blather on about without actually having tried it in practice... 
Want Fe (III) fast and cheaply? Dissolve some nails in a strong acid (HCl or H2SO4), not too dilute, oxidise iced Fe (II) solution by slow addition of
iced H2O2. All ingredients cheap as chips and no nasty chlorine to contend with either...
|
|
|
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! 
|
|
If you can get 30 -35% hydrogen peroxide then it is the best home oxidising agent available.
Cheap as chips, forms only water and oxygen as side products, what is there not to like?
|
|
|
LanthanumK
Hazard to Others
Posts: 298
Registered: 20-5-2011
Location: New Jersey
Member Is Offline
Mood: No Mood
|
|
AJKOER's method does work pretty well with steel wool. The combination of the hypochlorous acid, air, and moisture results in a moderately fast
corrosion rate. I have found the NaCl electrolytic oxidation method better.
hibernating...
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
And with 15 - 20 % HCl, gentle heating to get started, I dissolve steel wool in a matter of minutes. Then cool and slowly add cold H2O2 solution (32 %
from eBay, almost as cheap as bottled water). Now you have an FeCl3 solution, almost as concentrated as you want it to be and an excellent precursor
to most other Fe (III) salts.
Vinegar is about 0.8 M HAc: at best you can expect to dissolve about 20 g of Fe in a liter of that stuff!
|
|
|
AJKOER
Radically Dubious
Posts: 3026
Registered: 7-5-2011
Member Is Offline
Mood: No Mood
|
|
OK, in my opinion (see thread on HCl/H2O2 mixture), when HCl/H2O2 mixture gets hot (or is heated via an exothermic reaction on a metal) one may be
working with a very strong HOCl / HCl like mixture (on another forum, interestingly, one author reports a near runaway reaction between Iron and an
etching solution composed of HCl/H2O2).
So a possible improvement on blogfast25 method (which is very good if one is so inclined to invest the 32% H2O2 and the 20% HCl) is to create the
etching solution and react with Fe to form the ferric salt.
|
|
|
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 best approach for home chemists to iron II and III compounds is via steel wool, drain cleaner sulphuric acid, ammonium sulphate and hydrogen
peroxide.
This lets you make iron II sulphate in good yield or with the ammonium suphate from the garden centre the even better Mohr's salt. Mohr's salt is
readily crystallisable, air stable in solution and as the solid.
Reaction of steel wool with sulphuric acid, addition of hydrogen peroxide and ammonium sulphate yields iron alum. Once again very stable and
crystallisable.
Technical reagents to very pure starting materials. A couple of crystallisations and careful drying and you will have Mohr's salt and Iron alum good
enough to use as primary analytical standards.
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
SS:
I ‘produce’ (in a ‘cottage industry’ sense of the word) both Mohr’s salt and Ferric Ammonium Alum (FAA), then sell 100 g quantities of these
(once recrystallised) compounds on eBay. At my level (approx. 1 kg batches of the salts) calculation and experience shows that starting from FeSO4
hydrate (for FAA, add H2SO4, oxidise with 32 % H2O2, add ammonium sulphate, crystallise, then recrystallise once) rather than starting from scrap iron
+ ‘Draino’ H2SO4 is actually cheaper (not to mention easier)!
But I’ve yet to understand why sometimes the product comes out as amethyst looking crystals, and sometimes as clearish to slightly brown.
The slightly brown part I’m sure is just a bit of concentrated ferric solution clinging to the crystals (FAA isn’t easy to fully dry because it
has such a low melting point).
|
|
|
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!
|
|
I agree with you that starting from iron II sulphate is easier. I have seen some really nice iron II sulphate from garden centres, pale green plates
that would do duty in a lab, and some really vile ones, white powder with brown bits in it.
I suspect that the trick to amethyst crystals is to keep the solution quite acid, iron salts seem to hydrolyse slowly except in acid solution.
[Edited on 11-1-2012 by ScienceSquirrel]
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
Yes, the garden grade FeSO4 varies, that's my experience too. I buy 5 kg tubs of '99 %' from a decent supplier, cheaper than garden grade. Wonderful
green crystals, no oxidation or degradation in sight.
Yeah, I might try adding a few drops of conc. H2SO4 to the recrystallisation water to check that. My hopes aren't high though: FAA has 'natural
acidity'. Still, worth a try...
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
