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How does acid corrode a nail?

My name is Anna and I am in 7th grade. I was confused how a nail corrodes from an acid.

the atoms of the acid will break up the iron atoms of a nail into ions which is how an iron corrodes. IS THIS CORRECT?

ANNA K [last name deleted for privacy by Editor]
STUDENT - NORTH HILLS, California
2005

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2005

Chemistry is driven by imbalances that are very hard to understand completely but quite easy to understand in principal, Anna. The following should help you understand not just a nail corroding in acid but chemical reactions in general.

Suppose 4 boys & 4 girls from your 7th grade are going to go to a school dance together. You'll have 4 couples for steps where you dance as pairs. In chemistry, every atom must and does have the same number of protons as electrons, just as you must have an equal number of boys and girls for this type of dancing. Your 'atom' of four boys and four girls is also balanced because you have eight people for steps where you are supposed to dance as a ring of eight. Your group of eight, your 'atom' of 7th grade, does not need to interact with any of the other groups at the dance. Atoms of 'inert gases' are like your group, they are self contained and do not get involved in chemical reactions.

But suppose that 5 couples from 8th grade come to the dance and 3 couples from 9th grade. The 8th and 9th grade 'atoms' both have an equal number of boys and girls, as atoms must and do. But when it's time to dance as rings of eight, they can't do it as independent groups, the two groups must interact. Because one group has ten people and one group has six.

That is basically what happens in chemistry, the number of protons and electrons in an atom are equal, like the boys and girls in the dance, but this often means that the rings of electrons are out of balance. Metals have too many electrons to form stable rings, and the atoms in acids have too few. This causes the two atoms to try for a balance by the metal ionizing (sharing or giving up some electrons) and dissolving in the acid. But it's just a workable balance, not a perfect balance; so as temperatures and concentrations change, some subtle and harder to understand reactions can occur too.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A much simpler look at the question is an example. Assume that you have a pure iron nail (note that such a thing is not available in most places - it is an alloy) and you put it in a beaker with HCL-hydrochloric acid- also known as muriatic or swimming pool acid. The HCl will have some full molecules, but it will also have some H ions and some Cl ions. When it reacts with the steel, you will get some FeCl3 formed (some of that will also be ions in solution rather than a precipitate) and it will liberate some H2 or hydrogen gas. The rate of reaction is not a constant until an equilibrium is reached.

James Watts
- Navarre, Florida
2005

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2005

Thank you for the information.

I have another problem.

I don't understand why (science project) the nail outside of the vinegar ⇦in bulk on eBay or Amazon [affil links] (half the nail is in the vinegar in a cup)is rusting more than the part inside the vinegar.

And the rust outside of the vinegar; when I touch it, it comes right off, and dissolves in the vinegar.

ANNA K [returning]
STUDENT - NORTH HILLS, California

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2005

Uh oh. Teachers write us asking us to "Tell the kids to do their own homework!" And I'm afraid some are reading this and gloating: "Told ya so!"

If you read and understood the previous replies, why would you expect to see more rust on the part of the nail that is in the vinegar (acid), Anna?

The actual answer is that as long as there is acid present there will be no rust because rust dissolves into the acid easier than raw metal does. Where there may have been a splash of acid that dried up, the metal dissolved in the acid can't stay dissolved when the acid evaporates away, so it reacts with the oxygen in the air to form rust.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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Hi Anna,
You are asking for answers without having to do any work yourself.
Go to this sites FAQ section and you will find some of the information. Then do a search of the letters with "rust on nails" or similar. Try several variations and you will find the answer.
Ask yourself "what is rust" and "how is it formed" and you will have a head start once you answer that.
Then consider that the rust will dissolve in the vinegar. That should give you a clue, once you think about it for a while.
Come back with your answers and we'll agree with you or point you in a direction that is more correct.

James Watts
- Navarre, Florida
2006

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For my science project in grade 8 I have to redesign an old fire extinguisher... these old fire extinguishers had vinegar and baking soda in them so when they collided and mixed CO2 (carbon dioxide) was created to spray out the fire.

What I am trying to understand is what will vinegar corrode, so if this was an actual model would it work and not corrode from the vinegar?

Kelsey V [last name deleted for privacy by Editor]
student - Courtland, Ontario, Canada
2007

I understand that acid makes an iron nail rust, for example, citrus juice would make a nail rust, but WHY does acid make nails rust? Is there something in the acid that makes a nail rust? Or are there different kinds of acids that make a nail rust and some don't? if so, which acids make a nail rust and why? So many questions are in my head that search engines cannot answer. so I'm coming to you for help.

blair l [last name deleted for privacy by Editor]
student - kitchener,ontario,canada
December 9, 2009

Hi, Blair. Acid corrodes a nail, that is, the iron dissolves into the acid through the mechanism described above. It doesn't exactly make a nail rust, and it's important to be careful in wording such ideas.

The dissolved metal can react with oxygen in the air or water to form rust.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
December 2009