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What is Oxidation?

Oxidation is a chemical reaction where a substance loses electrons, often leading to its combination with oxygen. This process can result in rust on metals or the browning of an apple slice exposed to air. It's a fundamental concept in chemistry that affects everything from our cells to the stars. How does this invisible force shape our world? Let's explore further.
Michael Pollick
Michael Pollick
Michael Pollick
Michael Pollick

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.

Oxidized copper often develops a green hue or patina.
Oxidized copper often develops a green hue or patina.

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.

Oxidized metal gears.
Oxidized metal gears.

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.

A rusty I-beam.
A rusty I-beam.

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.

Rusty tractor.
Rusty tractor.

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.

Rusted truck.
Rusted truck.

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.

Michael Pollick
Michael Pollick

A regular AllTheScience contributor, Michael enjoys doing research in order to satisfy his wide-ranging curiosity about a variety of arcane topics. Before becoming a professional writer, Michael worked as an English tutor, poet, voice-over artist, and DJ.

Learn more...
Michael Pollick
Michael Pollick

A regular AllTheScience contributor, Michael enjoys doing research in order to satisfy his wide-ranging curiosity about a variety of arcane topics. Before becoming a professional writer, Michael worked as an English tutor, poet, voice-over artist, and DJ.

Learn more...

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Discussion Comments


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


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?


What material causes oxidation in a biochemical reaction?


Who discovered oxidation?


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.


Where do I find the two kinds of oxidation?


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


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?


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?


does the age of the penny contribute to the oxidizing?


what is the oxidation of benzene?


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?


I got what I needed! thanks!


is oxidation the same as patina?


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


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?


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?


Can you please tell me the date of the document.


what is rancidity?


how can you oxidize aluminum to alumina?


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?


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


this is great for kids. it's understandable.


can you make painted fabric look oxidized?


what is the difference between scale and rust?


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


Please give 10 example of oxidation reactions.


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


please give five examples of oxidation.


What is the most common form of oxidation?


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


excellent definition.


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?


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


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!


88 Rust is a type of oxidation.


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


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


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.


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!


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.


are oxidation and rusting the same thing?


Does oxygen oxidation kill bacteria in water?


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?


What type of change is oxidation?


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.


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


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


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


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


Thanks for the info guys but next time be specific.


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


good explanation. do more!


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


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?


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?


How can we speed up oxidation on living tissue?


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?


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.


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?


tell me about the oxidation process in textile printing.


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


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.


Does pH effect the oxidation of apples?


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


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?


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


why is corrosion considered oxidation?


does the age of the penny contribute to the oxidizing?


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.


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


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


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?


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?


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?


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


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.


How do we increase the rate of oxidation in apples?


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.


why do humans take antioxidants?


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


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?


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


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?


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 ?


I am doing my science fair project on oxidation.

Could you tell me some things that are affected

by oxidation? Thanks!


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

How is it involved?


"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.


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!!!!


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?


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!!!


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!


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


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


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:(


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!


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?


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!


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


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


Is there a difference between oxidation and oxidization?


Why must oxidation be accompanied by a reduction?


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?


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?


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.


is copper sulfate and copper oxide the same thing?


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


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?


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.

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    • Oxidized copper often develops a green hue or patina.
      By: SVLuma
      Oxidized copper often develops a green hue or patina.
    • Oxidized metal gears.
      By: psyberartist
      Oxidized metal gears.
    • A rusty I-beam.
      By: slgckgc
      A rusty I-beam.
    • Rusty tractor.
      By: Daniel Parks
      Rusty tractor.
    • Rusted truck.
      By: Michele Ursino
      Rusted truck.
    • Galvanized metal, like this bucket, resists oxidation.
      Galvanized metal, like this bucket, resists oxidation.
    • A freshly-cut apple will turn brown when it oxidizes.
      By: denphumi
      A freshly-cut apple will turn brown when it oxidizes.
    • Oxidation occurs when substances come in contact with oxygen molecules.
      By: nmcandre
      Oxidation occurs when substances come in contact with oxygen molecules.
    • The process of oxidation, or rusting, produces heat.
      By: jahina_photos
      The process of oxidation, or rusting, produces heat.