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Author Topic: do acids reduce metals?  (Read 204 times)

Offline William McC

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do acids reduce metals?
« on: 28/09/2016 01:30:23 »
Fluoroantimonic acid has the chemical formula HSbF6, and a molar mass of 236.76 g/mol. It is a very strong acid, in that it is capable of protonating almost anything, but that doesn't necessarily mean that it is the best at dissolving (eating through) materials.

I don't think that metals like steel are soluble in HSbF6, and protonating steel won't change its solubility, so really the question at hand is one about the chemical reactions:

HSbF6 --> H+ + SbF6
and
Fe + 2 H+ --> Fe++ + H2

These reactions indicate the dissociation of the acid into free protons (hydronium ions) and hexafluoroantimonate ions, and the reaction of protons with metallic iron (steel), resulting in soluble ferrous ions and hydrogen gas.

Based on this stoichiometry, it would take 2 moles of  acid to react with one mole of iron (molar mass of 56 g/mol). One kg of the acid contains just over 4 moles (1000/236.76 = 4.22 moles), so this would eat away 2.11 moles of iron, or roughly 120 grams.

In contrast, one kg of sulfuric acid, which is H2SO4, could consume roughly 560 grams of iron. Sulfuric acid is no where near as "strong" based on dissociation constant, but it has a much higher concentration of reactive protons per unit mass.

i hope this helps!

If you heat most acids they become more potent, sulfuric is one of them. It can reduce many metals like aluminum in seconds or minutes once it is hot. But it does not effect steel 55 gallon drums very much even when hot.

Sincerely,

William McCormick
« Last Edit: 02/10/2016 19:30:11 by chiralSPO »


 

Offline Bored chemist

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If you heat most acids they become more potent, sulfuric is one of them. It can reduce many metals like aluminum in seconds or minutes once it is hot. But it does not effect steel 55 gallon drums very much even when hot.

Sincerely,

William McCormick
Acids don't reduce metals they oxidise them; the acid gets reduced.
Hot acid will chew up mild steel (the stuff drums are made from) quite nicely. Cast iron is only slowly attacked by concentrated sulphuric acid.

 

Offline William McC

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If you heat most acids they become more potent, sulfuric is one of them. It can reduce many metals like aluminum in seconds or minutes once it is hot. But it does not effect steel 55 gallon drums very much even when hot.

Sincerely,

William McCormick
Acids don't reduce metals they oxidise them; the acid gets reduced.
Hot acid will chew up mild steel (the stuff drums are made from) quite nicely. Cast iron is only slowly attacked by concentrated sulphuric acid.

Reduction of the aluminum oxide coating occurs, and then the aluminum is oxidized once again, each time it removes a layer of the aluminum. Since an aluminum part can be totally eaten away in minutes, by the hot sulfuric acid solution that is held in a steel tank, a steel tank that lasts for about three months to six months. I would think that steel is not that effected by hot sulfuric acid. I used to cut and weld the 55 gallon drums for a carburetor rebuilding company.

Sincerely,

William McCormick
 

Offline chiralSPO

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If you heat most acids they become more potent, sulfuric is one of them. It can reduce many metals like aluminum in seconds or minutes once it is hot. But it does not effect steel 55 gallon drums very much even when hot.

Sincerely,

William McCormick
Acids don't reduce metals they oxidise them; the acid gets reduced.
Hot acid will chew up mild steel (the stuff drums are made from) quite nicely. Cast iron is only slowly attacked by concentrated sulphuric acid.

Reduction of the aluminum oxide coating occurs, and then the aluminum is oxidized once again, each time it removes a layer of the aluminum. Since an aluminum part can be totally eaten away in minutes, by the hot sulfuric acid solution that is held in a steel tank, a steel tank that lasts for about three months to six months. I would think that steel is not that effected by hot sulfuric acid. I used to cut and weld the 55 gallon drums for a carburetor rebuilding company.

Sincerely,

William McCormick

No. Acids do not reduce aluminum oxide. The might dissolve aluminum oxide, but certainly not reduce it.
 

Offline William McC

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Hot sulfuric acid does reduce aluminum oxide almost instantly. Cold sulfuric acid does not reduce it as much.

You can only oxidize aluminum so much, then it stops. They use AC current sometimes to anodize, to get deeper into the aluminum with a more uniform coating. If your anodizing tank gets to warm, you cannot anodize a thick layer of oxide on the aluminum, because the sulfuric acid eats it off. Or in some cases depending on the alloy of aluminum it will turn it black. 

The reaction is reduction then oxidation, reduction then oxidation in the hot sulfuric acid bath. That is why if you leave the carburetor body in the hot sulfuric acid for more than a few minutes it will no longer be there. All metal is coated with a layer of oxide, most acids have some other element that allows the acid to react with the oxide, and then allows it to react with the metal.


Sincerely,

William McCormick
 

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Hot sulfuric acid does reduce aluminum oxide almost instantly.


No it does not.
The aluminium in the oxide starts off and ends up in a +3 oxidation state no oxidation or reduction takes place and you clearly have no idea what you are on about.
Do you even realise that "reduce" is a technical term in this context?

https://en.wikipedia.org/wiki/Reducing_agent
 

Offline William McC

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Hot sulfuric acid does reduce aluminum oxide almost instantly.


No it does not.
The aluminium in the oxide starts off and ends up in a +3 oxidation state no oxidation or reduction takes place and you clearly have no idea what you are on about.
Do you even realise that "reduce" is a technical term in this context?

https://en.wikipedia.org/wiki/Reducing_agent

Aluminum oxide is reduced by the hot sulfuric acid, then raw exposed aluminum reduces the sulfuric acid. Back and forth back and forth.

Sincerely,

William McCormick
 

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Aluminum oxide is reduced by the hot sulfuric acid, then raw exposed aluminum reduces the sulfuric acid. Back and forth back and forth.

Sincerely,

William McCormick

It doesn't stop being wrong just because you repeat it.
 

Offline William McC

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Aluminum oxide is reduced by the hot sulfuric acid, then raw exposed aluminum reduces the sulfuric acid. Back and forth back and forth.

Sincerely,

William McCormick

It doesn't stop being wrong just because you repeat it.

Reduction is the opposite of oxidation. Now to get to the aluminum to oxidize it, you have to reduce the aluminum oxide, so that the acid can get to the pure aluminum and oxidize it. That is the problem in anodizing. Once the aluminum oxide is formed, in most areas it will not allow the acid in to finish off the missed areas. So they use AC current to burn off some of the new anodize coating, and hopefully get to the missed areas. This is somewhat successful.

youtu.be/RLkBzRnICZ4

Here is the reaction, it looks about right to me.

Sincerely,

William McCormick
 

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Aluminum oxide is reduced by the hot sulfuric acid, then raw exposed aluminum reduces the sulfuric acid. Back and forth back and forth.

Sincerely,

William McCormick

It doesn't stop being wrong just because you repeat it.

Reduction is the opposite of oxidation. Now to get to the aluminum to oxidize it, you have to reduce the aluminum oxide, so that the acid can get to the pure aluminum and oxidize it. That is the problem in anodizing. Once the aluminum oxide is formed, in most areas it will not allow the acid in to finish off the missed areas. So they use AC current to burn off some of the new anodize coating, and hopefully get to the missed areas. This is somewhat successful.

youtu.be/RLkBzRnICZ4

Here is the reaction, it looks about right to me.

Sincerely,

William McCormick

OK Now I see what it is that you don't understand.
You don't realise that it's possible to remove the oxide by protonation rather than oxidation or reduction (presumably because you didn't read or understand what I told you earlier about oxidation states)

The reaction which dissolves the aluminium oxide is this
Al2O3 +3 H2SO4  --> Al2(SO4)3  + 3  H2O
The aluminium remains in the +3 oxidation state throughout.

So, you are still wrong. The aluminium oxide is not reduced.
It would have been quicker and easier if you had accepted that in the first place and googled a bit af chemistry about oxides and acids

You would have found this sort of thing
http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/ions/acidsbasesrev2.shtml

This is the bit you should have looked for.
acid + metal oxide → salt + water
« Last Edit: 01/10/2016 16:18:13 by Bored chemist »
 

Offline William McC

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Aluminum oxide is reduced by the hot sulfuric acid, then raw exposed aluminum reduces the sulfuric acid. Back and forth back and forth.

Sincerely,

William McCormick

It doesn't stop being wrong just because you repeat it.

Reduction is the opposite of oxidation. Now to get to the aluminum to oxidize it, you have to reduce the aluminum oxide, so that the acid can get to the pure aluminum and oxidize it. That is the problem in anodizing. Once the aluminum oxide is formed, in most areas it will not allow the acid in to finish off the missed areas. So they use AC current to burn off some of the new anodize coating, and hopefully get to the missed areas. This is somewhat successful.

youtu.be/RLkBzRnICZ4

Here is the reaction, it looks about right to me.

Sincerely,

William McCormick

OK Now I see what it is that you don't understand.
You don't realise that it's possible to remove the oxide by protonation rather than oxidation or reduction (presumably because you didn't read or understand what I told you earlier about oxidation states)

The reaction which dissolves the aluminium oxide is this
Al2O3 +3 H2SO4  --> Al2(SO4)3  + 3  H2O
The aluminium remains in the +3 oxidation state throughout.

So, you are still wrong. The aluminium oxide is not reduced.
It would have been quicker and easier if you had accepted that in the first place and googled a bit af chemistry about oxides and acids

You would have found this sort of thing
http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/ions/acidsbasesrev2.shtml

This is the bit you should have looked for.
acid + metal oxide → salt + water

The solid aluminum oxide is no longer aluminum oxide and is washed away from the aluminum, it is now a liquid and part of a sulphur compound that you can use to deposit aluminum easily. That is what reduction meant the separation of the oxygen from a metal or an oxidizing compound like chlorine from a metal. Which that reaction does. You can make up a whole bunch of rules and definitions however they will quickly turn on themselves.

The history of reduction is the removal of oxygen or chlorine from a metal. Which this reaction does. The oxygen is replaced by the salt of sulfuric acid the sulphate. It was called reduction because it removes massive quantities of oxidized material from metal, or an ore, which is always an oxide of the metal. It often does this in seconds. That is the reason for the term reduction.

Sincerely,

William McCormick
 

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The solid aluminum oxide is no longer aluminum oxide and is washed away from the aluminum, it is now a liquid and part of a sulphur compound that you can use to deposit aluminum easily. That is what reduction meant the separation of the oxygen from a metal or an oxidizing compound like chlorine from a metal. Which that reaction does. You can make up a whole bunch of rules and definitions however they will quickly turn on themselves.

The history of reduction is the removal of oxygen or chlorine from a metal. Which this reaction does. The oxygen is replaced by the salt of sulfuric acid the sulphate. It was called reduction because it removes massive quantities of oxidized material from metal, or an ore, which is always an oxide of the metal. It often does this in seconds. That is the reason for the term reduction.

Sincerely,

William McCormick

Nonsense.
Apart from a lot of other things, the sulphate part of the molecule doesn't get involved.
The aluminium oxide is neither reduced nor oxidised.
Reduction is fundamentally a transfer of electrons. None takes place here.
 

Offline William McC

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The solid aluminum oxide is no longer aluminum oxide and is washed away from the aluminum, it is now a liquid and part of a sulphur compound that you can use to deposit aluminum easily. That is what reduction meant the separation of the oxygen from a metal or an oxidizing compound like chlorine from a metal. Which that reaction does. You can make up a whole bunch of rules and definitions however they will quickly turn on themselves.

The history of reduction is the removal of oxygen or chlorine from a metal. Which this reaction does. The oxygen is replaced by the salt of sulfuric acid the sulphate. It was called reduction because it removes massive quantities of oxidized material from metal, or an ore, which is always an oxide of the metal. It often does this in seconds. That is the reason for the term reduction.

Sincerely,

William McCormick

Nonsense.
Apart from a lot of other things, the sulphate part of the molecule doesn't get involved.
The aluminium oxide is neither reduced nor oxidised.
Reduction is fundamentally a transfer of electrons. None takes place here.



 Since my school, the defense plant I was part of growing up, and all the crazy business owners that I met, all taught or relayed to me that electrons are not orbiting or transferred, I would stick with my definition of reduction.

Sincerely,

William McCormick
 

Offline Bored chemist

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 Since my school, the defense plant I was part of growing up, and all the crazy business owners that I met, all taught or relayed to me that electrons are not orbiting or transferred, I would stick with my definition of reduction.

Sincerely,

William McCormick
Just as long as you make it clear that you are using your own, personal- shall we say "special" definition, (created by people that even you describe as "crazy") that's fine.

But please make it clear that when you say "reduction", you are using a crazy definition, rather than the useful one.

 

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