I had a feeling you were the same person as the original post I pasted.
Sandy had the original question and I was trying to help. The only thing I
still don't understand is exactly what the "complex" is that drives the
Fe203 to dissociate and reform this complex with Cl-. Is it some kind of
hydrated Fe complexed with Cl-?
Thanks Dan, that's my question exactly.
I can't see the difference between a ferric chloride complex and a
ferric acetate complex. The thing that drives the reaction in my
understanding is 6H+ + Fe2O3 --> 2Fe+++ + 3H2O
That formation of water is what moves the reaction to the right.
For me, salt is just going to cause problems down the line when it
sets up corrosion cells in the fine interstices of the previous rust
pitting. Unless someone can show that it is invaluable in the
derusting process with weak acids, I would advise to stay well away
from it. As I said, I far prefer mechanical derusting with a non-polar
solvent (kerosene or CRC) for anything valuable. YMMV
Just 2 comments:
1. It may just be that my chemistry was so long ago, but I'm not sure of the
usage of the term "complex" in this context. Are we calling an FeCl3
molecule a complex (I didn't think so)? My recollection is that a complex
had more to do with Van der Walls forces attracting surrounding molecules
such as the solvent to the ion or molecule in question, as if it were
chelated or sequestered. What is the complex that results from the
2. You have to admit that the NaCl is greatly accelerating the reaction
rate. Just do like I mentioned and sprinkle salt on a copper pan wetted
with vinegar. You will see the fastest reaction where the salt is. It
seems you are looking at this from the standpoint that salt does nothing,
and are challenging someone to prove otherwise. I think we are both
interested in the same thing, but maybe are looking at it from different
I guess it might be some sort of hydrated "complex". Like most ionic
species in aqueous solution. Our understanding of "complexes" seems to
coincide, although that's possibly and artifact of the age of our
chemistry learning (me ~ 45 years :)
That's the nub, I suspect, and why it is purportedly different from a
similar acetate "complex".
I can't disagree with you here, (never having tried it), but have
difficulty in explaining it to myself. I just hate salt!! It has
screwed up masses of our ag land and costs society squillions in
damage to just about everything. If it can be avoided, I will avoid
it. I once had a car at the beach where the radiator fell apart on the
outside (all the fins disappeared) while the inside was perfect.
Well no, but then copper is a different kettle of fish, being on the
other side of hydrogen in the electrochemical reactivity series.
Next time my wife asks me to get rid of some rust stains, and I have
no CLR (another weak organic acid sold for the purpose of removing
lime deposits and rust stains) I will try acetic acid with NaCl and
without. Stop watch and clip board at the ready! :)
Or fairly similar standpoints. I see the downside of introducing salt
to rusted metal, having lived near the beach for a long time.
On Mon, 17 May 2004 13:44:10 -0700, Larry Blanchard
Interesting. And do you expect everyone here to have this lack of
interest, like Charlie does?
I, for one, care why it is reported to work.
You appear not to have considered the downsides of soaking rusted
ferrous metal in salt solution? Museums have a hell of a job removing
salt from ferrous artifacts found in the sea.
If the rust is present as Fe203 then the iron is trivalent and will go
into the salt-acetic acid solution predominately as the FeCl6(-3)
complex. Note that there is no change in oxidation state of the iron.
That iron complex is a central trivalent iron ion (with a +3 charge)
which usually has a coordination number of six. That means there will
be six positions around that iron ion that are occupied by some
species. Since the concentration of chloride is so high relative to
the other anions the predominate species will be FeCl6(-3). The net
charge of the complex is -3 because each chloride carries a -1 charge
and the iron has a +3 charge. There certainly will be some anions
where an acetate ion and/or a hydroxyl ion will replace one or more of
the chlorides. For this discussion the exact composition of that iron
complex is not only unknown but is of no particular interest. Just
remember that if too many of the chlorides in that complex are
replaced by hydroxyls or acetates then the iron will precipitate as a
hydrous oxide or basic acetate and that is why one uses such a high
concentration of chloride.
It is the stability of that iron chloride complex and the whopping
excess of chloride ions that drives this reaction. The high solubility
of iron chlorides prevents the reaction from coming to a screeching
halt due to precipitated of hydrous iron oxides and basic acetates.
There is no oxidation or reduction reaction at this point.
That iron complex will oxidize iron metal. The simplified net reaction
2Fe+3 + Fe(0) --> 3Fe+2
This reaction is one that you don't want to happen because that Fe(0)
is the iron metal you presumably are trying to recover rust free. This
also should suggest to you why you should keep oxygen (air) out of the
Fe+2 is oxidized to Fe+3 by oxygen and the reaction takes place
readily because of the stability of the iron(III)-chloride complex. If
you allow air into the process you will be producing more Fe+3 which
in turn reacts with the iron metal (see the above reaction). If you
bubbled air through the solution this process will continue until you
run out of iron metal or the process gets bogged down by
precipitation. It is this reaction which will give you an etch line at
the liquid surface. Why?...because that is where the oxygen is.
This process works well with Fe203, less well with Fe304.
Since the concern about using chloride has been mentioned I will
address that issue as well. The chloride will be pretty well rinsed
off of the surface. The freshly cleaned iron surface is quite reactive
and needs some type of protection. If you keep iron dry it won't rust.
WD-40 is not a good option as it will pick up water.
Chloride can remain in microscopic cracks where it can accelerate
stress corrosion. If you are cleaning up an I-beam for a bridge this
process might not be a good choice. If you are cleaning a wrench e.g.
that is not an antique I wouldn't worry about stress corrosion. If I
am cleaning some tool that the kids left out in the rain I probably
will dunk it in a 5% solution of muriatic acid, rinse it and apply a
If you have a valuable antique get some advice from someone else as
cleaning may not be appropriate.
Why not use vinegar without the chloride? Vinegar is ~5% acetic acid.
Now for a little of the requested math. The dissociation constant of
HAc (acetic acid) is ~10^-5. (Ten to the minus five) In simplified
terms the H+ concentration in solution times the Ac-1 equals ten to
the minus five. Since the H+ = Ac-1 the acetate and the hydrogen ion
concentration in 5% acetic acid will equal the square root of 10^-5 or
somewhere around .02 molar. If someone wants to be picky it actually
calculates to be a tad more concentrated. That concentration of
hydrogen ions won't keep trivalent iron in solution.
This thread has stirred up some interest. I will stick with it at
least for a while. Let's see if this answers some of the questions or
if I have everyone more confused.
So with excess acetic acid present, "hydrous oxides or basic acetates"
will be precipitated? Surely they will be redissolved by the excess
acetic acid as soluble acetates?
What is formed from the stable soluble ferric acetate that is taken
out of the process?
If all this chloride is "taken out of the scene" what happens to all
those lonely sodium ions?
Surely excess acetic acid does the same thing?
Only when exposed to atmospheric oxygen, No?
Magnetite is quite resistant to any attack.
It usually just falls to the bottom as a black sludge IME.
WD-40 surely repels water. I suggest that heavily pitted iron which
has had salt solution soaking into the pits will be quite difficult to
That's what I said.
I thought you were contradicting this above.
Further corrosion? I would certainly not want that.
Wrenches in my hands suffer extreme stress. I've broken several :)
Hooley Dooley, how long will that last? What's wrong with a quick
squirt of CRC or WD 40 and a wipe with a rag?
And certainly don't use hydrochloric acid (shudder) or salt and
vinegar. Save the latter for your fish and chips :)
So you're saying that acetic acid won't dissolve Fe2O3?
It does for me. The label of my vinegar does not list sodium chloride.
I'm still struggling with your claim that ferric acetate in excess
acetic acid is unstable.
If you say that the sodium chloride keeps it in solution and stops it
precipitaing out as ~ ferric hydroxide, then that is not my
experience. I end up with a dirty yellow solution when I soak rust in
vinegar. I have never used salt in the vinegar, but next time I have
need to clean some rust, I will try with and without, to see if the
claimed speed increase occurs, or you claim of precipitation of ferric
hydroxide occurs and does not occur.
Museums soak very rusty items in sodium hydroxide solutions.
I believe this just stops further corrosion until the rust can be
removed by other means.
How so exactly?
Iron acetate is surely soluble enough?
Um, surely without the hydrogen ions, you are not going to get any
dissolution of anything in the first place. All you need is an anion
along with the H+ that does not form an insoluble precipitate with the
resulting iron ions.
Yep, that's what "weak" means wrt acids and bases.
Where you have infact neutralised all the acetic acid present.
No, it will remain a solution of iron ions, acetate ions, sodium ions
and chloride ions. The iron ions will slowly precipitate to iron
hydroxide complexes as the final H+ ions are used up. No?
Yes, if what you had was ferric chloride. You don't. You have a
neutral solution of the ions I just mentioned, surely.
You keep asking this question over and over. First, if you have ions they
are not "neutral". By definition an ion is electrically charged, hence it
is reactive. The solution is neutral because for each cation there is a
matching anion with the opposite charge, but the ions themselves are not
neutral at all. Second, chlorine is one of the most reactive of all
elements, hence any reaction involving chlorine will proceed at a higher
rate than one involving acetate. The end result is that by putting some
chlorine ions in the solution you end up with a faster reaction.
Reply to jclarke at ae tee tee global dot net
"The solution" is not what reacts with the rust. What reacts with the rust
is individual ions within that solution.
So what is a chlorine ion floating around with its electrical charge exposed
if not "elemental chlorine"? What comes in contact with the rust is not
sodium and chlorine bound, it's individual sodium ions and individual
I thought we were talking chemistry here, not physics. A monatomic ion is
not "stable" or "unstable" chemically--that's a property of a compound.
No, your understanding of what constitutes an ion is so wrong that you can't
follow the argument.
Reply to jclarke at ae tee tee global dot net
What ions are you claiming react with the rust (other than H+)?
Can you give balanced equations for this?
A chlorine ion!
Elemental chlorine with an extra electron!
And electrons are what give chemical moieties their chemical
Which apparently have no effect?
The dissolution/neutralisation of Fe2O3 is by H+ ions, surely.
I am talking chemistry. What are you referring to?
A chloride ion is more stable (less likely to change its chemical
state) than an acetate ion. A fluoride ion is even MORE stable!
Elemental chlorine and fluorine are most UNSTABLE.
Stability is, afterall, the ability to resist (chemical) change.
Ummm, OK. Could you explain then what constitutes and ion?
There is no argument. What we need explaining is why the presence of
sodium chloride in the vinegar is advantageous.
Nah. What we need to know is whether or not it WORKS. I, like most woodwrkers,
am not a chemist. Like most woodworkers, I have some tools that I either buy
with rust on them, or that are particularly susceptible to rust under certain
Somewhere about 5 posts ago, an OT should have been added to this thread.
"Bore, n.: A person who talks when you wish him to listen." Ambrose Bierce, The
Nonsense. What you're saying is that if you don't understand the mechanisms of
flight, you don't know that there are aircraft overhead.
Nothing to tell them. I know chemists, electrical engineers, computer
programmers and a host of other tech types. So what? Where did I say that
chemists shouldn't be woodworkers, incidentally?
Well, I probably won't either, but that's because I have used electrolysis for
How is a thread on ionization and covalents and whatever else pertinent to
restoring woodworking tools?
It won't matter to me, as I've just trashed this thread, but the fact is, none
of you seems capable of snipping, and there is absolutely no way for an average
woodworker to tell which of you guys is full of beans, so there's not much
value here to the woodworker. It remains a choice that may or may not work. And
that may or may not damage tools because of the presence of salt. Depends on
which of you a person chooses to believe, because there has been no coherent
and definitive explanation by anyone.
If that makes me selfish, so be it. If you think that's a new cutesy on my
name, then you're about 400 years behind the times there.
"Bore, n.: A person who talks when you wish him to listen." Ambrose Bierce, The
On 17 May 2004 13:37:10 GMT, email@example.com (Charlie Self)
No, I'm saying that if you don't understand flight, you can't
successfully pilot those aircraft.
Umm, the bit you snipped? Here it is again:
Now what point was that making?
So why are you apparently criticising my reasons for not recommending
salt and vinegar? Sheesh, we've got one guy who cleans tools left in
the rain by the kids with hydrochloric acid! And he claims to be a
Because it helps understand the chemistry of corrosion and how to stop
it and remove it. If you don't want to understand it, then why do you
read it? Do you not understand electrolysis?
I do hope you understand it enough to know the dangers involved.
To you, perhaps, but there are some of us benefitting from the
discussion. As I said previously, if you are not interested, why do
you read it?
And you apparently don't want to find out. That's fine, but why did
you join in, if that's the case?
Oh, salt damages them, but I might discover that the benefits outweigh
the disadvantages. But then you are not interested apart from
complaining that others are.
Not that you understand, apparently. But if you are not interested in
Complaining about a discussion others are having that you are not
interested in? Yes.
No, I realised the simiarity after I wrote it.
I decided not to pander to your sensibilities by changing it.
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