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What Is Oxidation?

Michael Pollick
Updated May 21, 2024
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A freshly-cut apple turns brown, a bicycle fender becomes rusty and a copper penny suddenly turns green. What do all of these events have in common? They are all examples of a process called oxidation.

Oxidation is defined as the interaction between oxygen molecules and all the different substances they may contact, from metal to living tissue. Technically, however, with the discovery of electrons, oxidation came to be more precisely defined as the loss of at least one electron when two or more substances interact. Those substances may or may not include oxygen. (Incidentally, the opposite of oxidation is reduction — the addition of at least one electron when substances come into contact with each other.) Sometimes oxidation is not such a bad thing, as in the formation of super-durable anodized aluminum. Other times, oxidation can be destructive, such as the rusting of an automobile or the spoiling of fresh fruit.

We often used the words oxidation and rust interchangeably, but not all materials which interact with oxygen molecules actually disintegrate into rust. In the case of iron, the oxygen creates a slow burning process, which results in the brittle brown substance we call rust. When oxidation occurs in copper, on the other hand, the result is a greenish coating called copper oxide. The metal itself is not weakened by oxidation, but the surface develops a patina after years of exposure to air and water.

what is oxidation

When it involves oxygen, the process of oxidation depends on the amount of oxygen present in the air and the nature of the material it touches. True oxidation happens on a molecular level — we only see the large-scale effects as the oxygen causes free radicals on the surface to break away. In the case of fresh fruit, the skin usually provides a barrier against oxidation. This is why most fruits and vegetables arrive in good condition at the grocery store. Once the skin has been broken, however, the individual cells come in direct contact with air and the oxygen molecules start burning them. The result is a form of rust we see as brownish spots or blemishes.

Oxidation can also be a problem for car owners, since the outermost layers of paint are constantly exposed to air and water. If the car's outer finish is not protected by a wax coating or polyurethane, the oxygen molecules in the air will eventually start interacting with the paint. As the oxygen burns up the free radicals contained in the paint, the finish becomes duller and duller. Restoration efforts may include removing several layers of affected paint and reapplying a new layer of protectant. This is why professional car detailers recommend at least one layer of wax or other protectant be used every time the car is washed.

The secret of preventing oxidation caused by oxygen is to provide a layer of protection between the exposed material and the air. This could mean a wax or polyurethane coating on a car, a layer of paint on metal objects or a quick spray of an anti-oxidant, like lemon juice, on exposed fruit. Destructive oxidation cannot occur if the oxygen cannot penetrate a surface to reach the free radicals it craves.

This is why stainless steel doesn't rust and ordinary steel does. The stainless steel has a thin coating of another metal which does not contain free radicals. Regular steel may be painted for protection against oxidation, but oxygen can still exploit any opening, no matter how small. This is why you may find a painted metal bicycle still damaged by rust.

All The Science is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
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Michael Pollick
By Michael Pollick
As a frequent contributor to All The Science, Michael Pollick uses his passion for research and writing to cover a wide range of topics. His curiosity drives him to study subjects in-depth, resulting in informative and engaging articles. Prior to becoming a professional writer, Michael honed his skills as an English tutor, poet, voice-over artist, and DJ.
Discussion Comments
By anon1002823 — On Feb 24, 2020

How did you do all of this awesome research!!!

By anon973629 — On Oct 13, 2014

I have older glass tumblers with painted designs that have changed to a pewter or nickel-like color on the surface of the paint. Is this oxidation? Is there a way to bring the original design back?

By samira — On Oct 20, 2012

What material causes oxidation in a biochemical reaction?

By anon252219 — On Mar 04, 2012

Who discovered oxidation?

By anon235582 — On Dec 18, 2011

I use brass ingots for sand casting and while making these ingots, a lot of BA135 Brass Bronze flux is added to make the ingot brittle. This is a chemical which belongs to the fluoride family.

I get a lot of brown spots on the surface of the casted pcs. Why is this? The spots appear randomly and more so when exposed to marine conditions. They may appear in a pc from one lot and may not in other pcs from the same lot.

By anon229872 — On Nov 16, 2011

Where do I find the two kinds of oxidation?

By anon216577 — On Sep 22, 2011

Will you please explain the purpose of oxidation and diffusion process? Thank you. I really needed it on our research.

By anon206105 — On Aug 15, 2011

Great article. I have a question for the panel. I am a landscape architect and have a water feature that is using corten steel (or A-606 steel) panels. The panels are going to be in constant contact with water, but not air. In other words, the steel will be submerged in water. How is the oxidation process affected in this case? Is it sped up? Slowed down?

We are worried about the orange residue that is produced by the oxidation and this residue discoloring the water. During construction, the orange color was prevalent. We are concerned on how long this residue might affect the color of the water. And, should we paint the steel as you suggest in your article as a short term solution?

By anon189703 — On Jun 23, 2011

Say you have a copper plate screwed down to a roof with stainless steel lags. would this cause any adverse chemical reactions like some type of oxidation? or are these two metals compatible with no problems?

By anon175607 — On May 13, 2011

does the age of the penny contribute to the oxidizing?

By anon165316 — On Apr 04, 2011

what is the oxidation of benzene?

By anon163652 — On Mar 28, 2011

I have an aluminum flag pole that has two pieces. I have used it for years with no discoloration on the pole. At another place, near gas drilling, I had one piece in the outside bracket and the other in the garage. Over a short period of time, the outside piece changed colors from aluminum to brown. I think it oxidized. Can someone help tell me what happened?

By anon162809 — On Mar 25, 2011

I got what I needed! thanks!

By anon156461 — On Feb 27, 2011

is oxidation the same as patina?

By anon153934 — On Feb 18, 2011

I am doing a science project and my dad said to do some terms. One of them was oxidation. This was very easy to understand. Thanks. --Brie

By anon147683 — On Jan 30, 2011

Can i please get some help? If we insulate rubber on bare copper and after that put it in a steam boiler for curing for two hours, why does the copper color change to reddish black? Can this be prevented and can it retain its original color?

By anon145014 — On Jan 21, 2011

for science fair this year I'm doing 'what is the affect of different substances on how quickly the apples will turn brown?' i have to do a research page about oxidation but I can't find anything. can you help?

By yeyerockz509 — On Jan 17, 2011

Can you please tell me the date of the document.

By anon141685 — On Jan 11, 2011

what is rancidity?

By anon139536 — On Jan 05, 2011

how can you oxidize aluminum to alumina?

By anon138088 — On Dec 30, 2010

Earth science is not my best class. When my teacher assigned us a project I had to ask.

"What are some examples of oxidation that is not metal rusting?" Can anyone answer that for me?

By anon131527 — On Dec 02, 2010

This is such a great article. It helped me write an essay on "why apples turn brown." Thanks! --Emily

By anon112879 — On Sep 22, 2010

this is great for kids. it's understandable.

By anon103246 — On Aug 11, 2010

can you make painted fabric look oxidized?

By anon101808 — On Aug 05, 2010

what is the difference between scale and rust?

By anon91739 — On Jun 23, 2010

Stainless steel doesn't rust because it forms an oxide compound that clings to it and prevents further oxidation, contrary to the above.

By anon87533 — On May 31, 2010

Please give 10 example of oxidation reactions.

By anon85670 — On May 21, 2010

thanks. this really helped for my science project on the oxidation of iron.

By anon79931 — On Apr 25, 2010

please give five examples of oxidation.

By anon78683 — On Apr 19, 2010

What is the most common form of oxidation?

By anon76463 — On Apr 10, 2010

Could you explain to me what mitochondrial oxidative capacity is? I am really having a hard time. Thanks for any help you can give.

By anon75385 — On Apr 06, 2010

excellent definition.

By anon74877 — On Apr 04, 2010

i'm doing a project on rust and oxidation. But i have no idea what i'm going to do with it. can you help me?

By anon73859 — On Mar 29, 2010

On my notes it has a +I and T1 as "oxidization." what does it mean?

By anon67340 — On Feb 24, 2010

I am doing a science project on how oxidation affects a sliced apple, and I need some info on that! Please, please tell me some info!

By anon66746 — On Feb 21, 2010

88 Rust is a type of oxidation.

By anon65262 — On Feb 11, 2010

Will aluminum such as an aluminum bike frame rust or oxidize?

By anon62513 — On Jan 27, 2010

I am doing oxidation process for making oxidized polyethylene wax by using air. Here what is reaction take place.

By anon62333 — On Jan 26, 2010

my comment for the number 90. i think you got it all wrong when you placed them inside a jar, because by doing that, oxygen is still "intact" therefore the fruit does not rot -- or something like that. I'm not very good in the science stuff but I'm pretty sure that putting it in a jar made the experiment a failure.

By anon62059 — On Jan 24, 2010

Wow! This really helped me. I had to do a science fair project on the oxidation of apples, and this gave me like all the info! Thanks!

By anon59860 — On Jan 10, 2010

For my science fair i put an apple slice in three glass jars. in one i put salt, in the other i put sugar, and the last i put nothing for the control group (all along with the apple). Then i closed off the jars.

I was trying to see which was a better preservative. But none of the three apples turned brown or rotted. They were all the exact same after two days as they were when they first went into the jar. Why? Now i am screwed for science class because i have no results to graph.

By anon59159 — On Jan 06, 2010

are oxidation and rusting the same thing?

By anon58495 — On Jan 02, 2010

Does oxygen oxidation kill bacteria in water?

By lucky45 — On Dec 05, 2009

I ball mill Aluminum to get powdered Al. But oxidation degrades it and does not burn fast enough

(PUFF) and is not pure enough. I put two fittings on my barrel,and am going to purge it with Co2, and purge it every other day or so. Do you think it will help?

By anon54759 — On Dec 02, 2009

What type of change is oxidation?

By anon53168 — On Nov 19, 2009

I am doing a project that includes oxidation. I don't fully understand what it is. can you help me out? I feel kind of stupid.

By anon50041 — On Oct 25, 2009

what would happen to an iron nail, therefore in saltwater?

By anon49638 — On Oct 21, 2009

Is it possible using air ionizers can slow oxidation on the metal?

By anon47902 — On Oct 08, 2009

this is pretty good, but you should also add an experiment with something like hydrogen peroxide.

By anon47390 — On Oct 04, 2009

I think a good idea would be to include an atmospheric oxidation reaction to show how it can effect the environment.

By anon46563 — On Sep 27, 2009

Thanks for the info guys but next time be specific.

By anon46014 — On Sep 22, 2009

i'm so glad to find this website cause i needed a lot of info for my science fair project. Thanks!

By anon44913 — On Sep 11, 2009

good explanation. do more!

By anon41890 — On Aug 18, 2009

what conditions are necessary to make oxidation (rust) possible?

By anon38044 — On Jul 23, 2009

just a thought. is oxidation ever been used to power a generator? if the reaction between 2 elements/compounds is strong enough, is it possible?

By anon35353 — On Jul 04, 2009

I'm thinking of using plumbers solder for a craft project involving an outdoor table, bending it around the legs like a vine. What will it look like after it oxidizes?

By anon30673 — On Apr 22, 2009

How can we speed up oxidation on living tissue?

By luther — On Mar 25, 2009

Oxidation is addition of oxygen, in terms of oxygen

at the same time during burning oxygen gets added up.

so what is the difference between oxidation and burning?

By anon28501 — On Mar 17, 2009

I'm doing a science project on which solution decreases the rate of oxidation and I'm a little confused on the meaning of oxidation in the kind of project I am doing.

By anon26886 — On Feb 20, 2009

When I was younger I could see what I now think are molecules in the air. This would only happen at night and my room was filled with tiny little dots. My daughter now describes the same thing to me that she sees, although she says that the air is "thick" at night. What are we seeing?

By anon26866 — On Feb 20, 2009

tell me about the oxidation process in textile printing.

By anon26648 — On Feb 17, 2009

question: for my science assignment...i thought that how reactive elements are depends on their outer valence shell, and if one element is trying to gain electrons and the other is trying to lose electrons, then there will be a strong reaction. so for example, copper sulfate and zinc; copper has a outer shell of 11 electrons and zinc has a outer shell of 12 electrons, that means they are both trying to gain electrons since they have more than half of their outer shells full right? but from the sheet teacher gave me, said that zinc should give copper 2 electrons and become an ion and copper receives 2 electrons from zinc and becomes an atom.

so just really confused...can someone help me out? oh and thanks for reading all that =D

By anon24163 — On Jan 08, 2009

To Anon16401: The oxygen and hydrogen in the water are bonded together so unless you mix air into the water there is very little free oxygen in the water

Re: anon 22297: oxidation would only go faster in more oxygen until a thick layer of copper oxide formed. Then the rate-limiting step would likely become the oxygen moving through the oxide to the copper metal.

By vannavaught — On Dec 02, 2008

Does pH effect the oxidation of apples?

By anon22297 — On Dec 01, 2008

if there is oxygen present, the copper rod wouldn't be in a vacuum - which is the absence of any gas. And yes, corrosion would occur more quickly, as the environment would be more oxygen rich than normal air, which only has 21% oxygen content

By anon21007 — On Nov 08, 2008

If i placed a rod of copper into a vacuum, which was filled with O(sub 2), would:

a.oxidation even be able to occur in a vacuum

b.would the oxidation of the copper occur faster than it would in normal conditions?

By anon19652 — On Oct 16, 2008

to anon18094 : corrosion is considered oxidation because oxidation when you are taking about metal it corrodes or breaks down.

By anon18094 — On Sep 15, 2008

why is corrosion considered oxidation?

By anon17722 — On Sep 05, 2008

does the age of the penny contribute to the oxidizing?

By anon17652 — On Sep 03, 2008

the layer that forms on the aluminum is like a patina, protective layer,when it is in contact with the atmosphere. this layer is known as aluminum oxide layer. aluminum is its pure state has a melting point of @660 degrees C,when this oxide layers forms the melting point increases to over 2000degrees C.

By anon16770 — On Aug 14, 2008

is it possible to remove oxidation through heat? for example, will melting an oxidized metal remove the oxygen?

By anon16401 — On Aug 05, 2008

to the editors reply, if water is made up of hydrogen and OXYGEN why doesn't it oxidize?

By anon15730 — On Jul 20, 2008

I placed an apple in water but after forty minutes, it did not oxidise. I repeated it and the same thing happened. Why is this so?

By anon15308 — On Jul 07, 2008

How long does it take for oxidation of paint to occur. If oxidation is removed from a painted material, how long would it take for the area to be covered by oxidation again?

By anon14565 — On Jun 19, 2008

Aluminum is a fairly reactive metal that often has a protective layer on due to oxidation with the air. what is the protective layer called? Please can you tell me?

By anon14553 — On Jun 19, 2008

hey i would like to know if the temperature of the surroundings really affects the rate of oxidation in apples. And i would like to know what is the room temperature of a normal room at 12 noon. Thanks

By anon14312 — On Jun 14, 2008

To anon12690, Can you tell me the procedures of your experiment? D: like for example you soak one apple in lemon juice, then what about those other apples, do you place them in water or leave them exposed in air to compare. because im supposed to design an experiment and it is sort of similar to yours.

By anon13061 — On May 19, 2008

How do we increase the rate of oxidation in apples?

By anon12690 — On May 12, 2008

lemon juice is good to prevent oxidation...i did an experiment with apples and the one with lemon juice look edible... except it tasted sour XD. so what is it exactly which prevents oxidation occurring when you use lemon juice? is it the vitamin C?? thank you to this site!! explained oxidation to me in simple english.

By anon12326 — On May 04, 2008

why do humans take antioxidants?

By anon11965 — On Apr 27, 2008

Say an apple is in a closed environment and uses up all the oxygen in oxidation, what happens to the apple after that?

By jamezter — On Apr 23, 2008

So the more oxygen the more oxidation occurs? or the more water there is the more oxidation occurs? Let's say the water is actually RO water. Will there be any oxidation?

By anon11629 — On Apr 20, 2008

what do you call the loss of oxygen in a reaction? oxidation or reduction? can someone please explain the difference between the two.

By elijah — On Apr 10, 2008

The above article is good. It would be better if a few redox reactions were explained in terms of oxidation number method. How about galvanic cells?

By anon10820 — On Apr 03, 2008

in some process oxidation is required and which is very necessary ? ozone is an oxidizing agent and it is very powerful ? could you explain me why oxidation is required ?

By garec111 — On Mar 21, 2008

I am doing my science fair project on oxidation.

Could you tell me some things that are affected

by oxidation? Thanks!

By anon9504 — On Mar 07, 2008

How is oxidation something you need to determine iodide content in salt?

How is it involved?

By anon8413 — On Feb 13, 2008

"Posted by: juliette

is copper sulfate and copper oxide the same thing?"

No, Copper Sulphate is when copper, or something containing Copper, reacts with Sulphur or something with Sulphur in it. It contains S (sulphur) and Cu (copper) molecules.

Copper oxide is formed when Copper, or something containing Copper, reacts with Oxygen or something with Oxygen in it. It contains O (oxygen) and Cu (copper) molecules.

By sciencechic1 — On Feb 01, 2008

please mail me with tips and everything for my science fair project. i need help on the things that vitamin C does to fruits and vegetables and oxidation!!!!

By anon7202 — On Jan 20, 2008

I have to get this thing about oxidization and why things don't oxidize with vit. C and something like elplyhms or whatever. Soo... any pointers?

By anon5929 — On Dec 10, 2007

hi!! i'm doing a science project on oxidation i need help on how oxidation affects apples and how they rot. i need help please reply ty!!!

By anon5675 — On Dec 03, 2007

hi! I'm doing a science fair experiment on oxidation on pennies. i was wondering does oxidation happen over time or does there have to be a chemical laid on top to make oxidation happen? thanks!

By anon5627 — On Dec 01, 2007

Hi, I'm doing this project, and I have to say it is really fun to see object oxidate. Thanks for helping me.

By anon5611 — On Dec 01, 2007

I'm doing a science project on antioxidants, and I need to find out how exactly antioxidants prevent oxidation.

By anon5071 — On Nov 12, 2007

I am trying to do my homework and my teacher said that I have to find some everyday examples of oxidation. Can you please give me some pointers? I'm stuck:(

By anon4966 — On Nov 07, 2007

Hello, I was very happy to find this article online because I'm doing my science fair project on which type of antioxidants best prevents oxidation in an apple. So I'm trying to read up the most I can on the process of oxidation. Can someone tell me a little bit more about the chemical reactions between the substance in the apple and the oxygen - which creates oxidation? Any other information would be extremely helpful as well. Thank you!

By anon4842 — On Nov 03, 2007

I was glad to find this article although there are some errors it will do just fine for my science fair project and report. Any comments on oxidation being used in invisible ink?

By airin — On Oct 30, 2007

Hello, I was very happy to find this article online because I'm doing my science fair project on which type of antioxidants best prevents oxidation in an apple. So I'm trying to read up the most I can on the process of oxidation. Can someone tell me a little bit more about the chemical reactions between the substance in the apple and the oxygen - which creates oxidation? Any other information would be extremely helpful as well. Thank you!

By anon4516 — On Oct 21, 2007

What about oxidation in the body? Do antioxidants help prevent that process?

By anon4350 — On Oct 14, 2007

I was wondering if oxidation would have any effect on the pH.

By anon4267 — On Oct 10, 2007

Is there a difference between oxidation and oxidization?

By anon4210 — On Oct 08, 2007

Why must oxidation be accompanied by a reduction?

By anon4060 — On Oct 01, 2007

I'm doing this science experiment about whether oxidation occurs in apples in different levels of ph water. do you think that ph levels will have an effect?

By tu2dogs — On Aug 03, 2007

what about protection against the oxidation rxn between free O2 and steel by utilizing a cathodic protection mechanism such that a constant supply of electrons is emitted from the surface requiring protection. In the case of the classic experiment wherein steel wool is partly immersed in water, could not one test this hypotheses by passing a low level charge through the steel wool?

By anon2851 — On Jul 28, 2007

Ummm... Metals don't contain free radicals. Free radicals are involved in some oxidation processes, but the main reason some metals oxidize in air and others don't is that for many metals, once they are coated with oxide, they do not oxidize further. The reason stainless steel does not rust is that it is mixed with nickel and chromium, and these form a layer of oxide that prevents the bulk from oxidizing. Something similar occurs with aluminum; aluminum becomes coated with aluminum oxide, which under ordinary conditions prevents the metal from oxidizing further. However, if aluminum is powder and mixed with a powdered oxidizer, it can burn quite rapidly; in fact this is used as a "flash powder" for fireworks.

By juliette — On Jun 03, 2007

is copper sulfate and copper oxide the same thing?

By Este — On May 06, 2007

If a skin care product becomes rancid, is this considered oxidation?

By Este — On May 06, 2007

if you have an emulsion, and with the effect of time or temperature, it becomes thin and watery, what is the scientific term for this occurrence? It's not oxidation is it?

By anon414 — On Apr 24, 2007

Does oxidizing have anything to do with bacteria? I have an experiment and the question is "Does vitamin C prevent fresh food from rotting (oxidizing)? My teacher said the topic was bacteria.

Michael Pollick
Michael Pollick
As a frequent contributor to All The Science, Michael Pollick uses his passion for research and writing to cover a wide...
Learn more
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