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What is rust? and how does pH effect this?


I'm doing a science experiment on how pH level effects rust I want to find out how rust forms? and how different levels of pH might effect this. If you have any information please tell me. (8th grader)

Alison Adeleted
- Morton Grove, Illinois


All the information that you have requested will be available if you refer to Ellingham's diagram or the E-pH diagrams. You will certainly find these in college level chemistry books.

I hope this information helps you


Ajit Menon
Alden, New York


Alison - Rust is the natural state of iron (ferrous oxide). Rust occurs when an exposed area of a ferrous (iron-containing) alloy (like steel) drops below a pH of about 8.2 or 8.3. Rust inhibitors provide an environment that combats the pH drop on the surface - thereby protecting and preserving the surface finish. Different types of rust inhibitors provide different ways and durations of corrosion protection. By the way - water is the culprit that starts the rusting process. The water doesn't even have to be in a liquid state - it can be the humidity in the air. That is one reason cars in Chicago rust faster than cars in Phoenix - because Phoenix has very low atmospheric humidity compared to Chicago. Hope this helps.

Dan Brewer
chemical process supplier - Gurnee, Illinois


Once along time ago there were only two animals, The fish and the bat. The bat ate the fish, but the bats had to stay close to the land. So the bats ate a lot of pond, lake, and river fish. But they could only go so far out to sea. So when winter came very few fish lived in the fresh water because all the bats ate them. So there were a lot of uneaten fish at sea. So when winter comes the fresh water becomes frozen and the ocean water is not this is because the fish warm the water.

Dura Pdeleted
- U.S.S.R.

sidebar ++

I have no doubt that you have given a very good explanation of why the oceans don't freeze, Dura. But the question was how pH level affects rusting, and I got thrown off the sequitur somewhere along the line :-)

P.S.: I don't think there is a U.S.S.R. anymore, Dura, and your IP address shows you to be in Jax, Florida. Remember to be careful on the internet because you are not as anonymous as you think.

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Ted Mooney, P.E. RET
Brick, New Jersey

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Hey, I'm in 9th and I'm doing the same project, whether different pH's affect iron and the rusting process of it, hhahaa COOOOOLLL!

- Chalfont, Pennsylvania

sidebar +++

I am doing a project on rust too. This is so weird. I am here researching my project and I stumble onto this site which ROCKS!

Katmie F deleted
future Doctor and Newswoman - Louisville, Kentucky


People have from time to time offered a generous assessment of our efforts here, Katmie. But this is the first time we old fogies have been told that our site Rocks. Thanks!

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Ted Mooney, P.E. RET
Brick, New Jersey


I did a project on that too. I won 2nd place in science fair. Thank you so much for your help!

Marilyn F deleted
student - Houston, Texas


Hi. I'm doing a science fair project along the same lines as this conversation. I am testing a number of pops ie. Coke, Pepsi, Sprite, etc. for how much they will rust an iron nail. I would like to know if in fact these pops will rust an iron nail and if so how they are doing so.

Thanks a lot!

Adam F deleted
- Calgary, Alberta, Canada


I'm doing that science fair project too! We used Lemon Juice, Water, and Ammonia, because they have different pH. Ammonia has the lowest pH and it rusted the most. Hope this helps!

Jewel B deleted
- Taylor, Missouri


Hi! I'm a 3rd year High school student and I doubt why the rate of rusting is fast if you place it in a pH level below 7.

Sol Tdeleted
Science and Technology - Butuan City, Philippines


I wanted to make a small correction to the comment made by Dan in regards to water and rust. Water is not the culprit in is the pollutants and contaminates carried in the water. The oxidization process is caused by such things as electrostatic charge caused by contaminates like acid...pure water does not do that. The Chicago/Arizona comparison has many other factors...Chicago and snow states utilized salt to deice roads which is carried in the water and sticks to your care causing the electrostatic process to begin. Pollution carried in the water is also a major factor. The humidity in Chicago allows the contaminated water to stay on the surface is not just cause the metal is wet. Hope that helps...

- Port Hueneme, California


After my previous reply, I dug out my old engineering manuals and this is generally what it states about corrosion. You need three things to occur to have rust:
1.The metal needs to be in contact with an electrolyte (something that conducts electricity -- water or gases can be electrolytes). These carry electric currents.
2.The presence of corrosive agents. Pure distilled water does not function as an electrolyte and will not corrode metal.
3.The electrical connection where the metal becomes charged through the chemical reaction between the mental and contaminates (electrically connected and carried by the electrolyte). The loss of metal atoms in the reaction causes rust.

- Port Hueneme, California


Hi. I am doing the same project and I am also in 8th grade. Interesting what the 4th result on google for "does pH effect the rusting of iron?" is. Anyway, I've been doing some research myself... here goes... (This is NOT copy-pasted, it is in MY OWN words)

Rust occurs when an area of an iron-containing substance drops below a pH of about 8.2. is common because iron combines very readily with oxygen. So readily, in fact, that pure iron is only rarely found in nature. Contrast to popular belief, water is not the actual cause of rust. Pure water will not cause rust to form on the iron. It is contaminants and alien particles in the water that cause electrostatic charges (electrolytes), such as acid. For pH values below 4.0, iron oxide (FeO) is soluble. Thus, the oxide (oxygen) dissolves as it is formed instead of depositing on the metal's surface. With the oxide gone, the metal surface is in direct contact with the acid solution, and the corrosion reaction proceeds at a greater rate than it does at higher pH values. For pH values greater than pH 10, the rusting rate seems to fall as pH is increased.

Sam Fdeleted
- Austin, Texas


That's great work for an 8th-grader, Sam. Now a little testing to confirm or refute what your research claims . . .

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Ted Mooney, P.E. RET
Brick, New Jersey

April 19, 2008

I'm doing a thing on rust too!

Emily Sdeleted
Student - Ottawa, Ontario, Canada

Earth Science for Every Kid


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Pop Bottle Science


Award Winning Science Fair Projects


May 7, 2008

Hi, I am a Freshman in high school.
I have been trying to figure out a way to make a generator using the water cycle, and I was wondering if metal rusts faster when the water is applied with pressure in the form of steam or liquid. I was also wondering if pure water still won't rust the metal when applied with a lot of pressure.

Spade A deleted

9th grade student - Hamer, Idaho

July 23, 2008

Heys, I'm also doing a project on corrosion, but if pure water isn't supposed to cause corrosion, then why does it in reality?

Tyler E deleted
- Russellton, Pennsylvania

Hi, Spade; Hi, Tyler. Water conducts electricity in a different way than metals.

In a metal, electrons can be made to sort of bounce from one atom to the next to the next to the next, effectively carrying current.

Water is not of a structure that allows electrons to bounce along from atom to atom that way. Rather, the way water carries electricity is that charged particles (called ions) drift through the water from one place to another, carrying a charge with them. But if the water is truly pure, with nothing dissolved in it, there are no ions dissolved in it, so it can't conduct electricity.


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Ted Mooney, P.E. RET
Brick, New Jersey

January 4, 2009

So reading some of the responses...I'm getting confused to when rust occurs. Does it occur at a acidic level or basic level. Below a pH of 8.2 would make it lean toward the acidic scale right?

Linc Sdeleted
- San Francisco, California

January 5, 2009

Yes it is confusing, Linc, that doesn't mean that anyone is trying to mislead you, just that it is a bit of work to understand it all.

For example, bleach is murderously corrosive and quickly causes rust, even though the pH of bleach is somewhere around 12. But the corrosivity of bleach is not because of it's pH, it's because of other properties of the bleach including it's chloride content and the way it generates nascent oxygen. In general, a high pH will tend to slow down or stop rust. Iron or steel will last just about forever sitting in a vat of pH 12 water (water to which sodium hydroxide / lye has been added and nothing else). Iron (steel) doesn't dissolve in alkali, it remains iron.

But at the low pH end (that is, the acid end), iron or steel dissolves into the acid. So acids are very corrosive! But guess what . . . you may not see rust. That's because rust will dissolve into the acid even more readily than the iron. If you were to put slightly rusty steel into vinegar, the first thing you would see is the rust dissolving. But if you were to spritz vinegar onto steel, the vinegar will dissolve a little of the steel and, as it dries, that steel can no longer remain dissolved, but will become rust. Similarly, the acid can become exhausted from dissolving all the iron it can hold, then it will turn rusty.


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Ted Mooney, P.E. RET
Brick, New Jersey

January 22, 2009

I am doing a similar science project...and your comment was very helpful Ted! I was confused at first but now I understand. Thanks!

Kate Bdeleted
- Louisville, Kentucky

February 27, 2009

lol I'm in 5th grade and I'm doing it as well. this info given is very explanatory.

Oliver Cdeleted
- Singapore

March 14, 2010

I'm doing corrosion with iron too. For my solvents, I will be using hydrochloric acid, lemon juice, beer, corn, milk, pure water, baking soda, hand soap, lime, and sodium hydroxide. Are these solvents a good independent variable for the experiment of: Does the pH effect the corrosion rate of iron?

Angela Ydeleted
- Sydney, NSW, Australia

November 9, 2010

I'm doing a similar project, and I was wondering: If I use a chemical to change the pH of the solution in which I'm soaking the iron, how can I be sure that a part of the compound, and not the pH, is what's changing the rate of reaction?

Blaise Ndeleted
- Jax, Florida

February 8, 2011

First of all, thank you Mr. Ted Mooney for this site and your input, but I have a question on the pH effect on rust. I use distilled water with a pH of 7 but I can see that the water turns more rusty as compared to the vinegar with pH of 4. I cannot explain this. Can someone help please?

Victor Jdeleted
- Santa Rosa, California

February 8, 2011

Hi, Victor

The vinegar is, as you note, an acid. Just as salt can dissolve into water and sort of disappear, acids dissolve rust. The formula is probably something like this:

Fe2O3 + 6HC2H3O2 ==> 2Fe(C2H3O2)3 + 3H2O


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Ted Mooney, P.E. RET
Brick, New Jersey

June 7, 2011

Hi. I've conducted an experiment varying the pH (2 to 6) in which corrosion of a steel takes place. For my result, I found out that pH 2 and pH 5 corroded the most while pH 6 corroded only slightly better than pH 3 and 4. I know that HCl (the acid I used) can be used to remove rust at a low concentration, is that why pH of 3 and 4 did little corrosion? If so, is there a chemical proof of why pH 5 works, pH 3 and 4 don't but pH 2 does again?

Thank you so much.

Allison R
- New York City, New York, US

June 6, 2011

Hi, Allison.

Before attempting to explain experimental results, you need to be really sure of them. "Explaining" why something happens, if it fact it doesn't, is a pretty clear road to a failure. Your results might be right, but I don't think they are.


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Ted Mooney, P.E. RET
Brick, New Jersey

March 14, 2012

Hello, I'm glad I found this site, it helps understanding the reactions that happen since I wasn't able to ever be in a real chemistry class.
I'm a senior in HS and I'm currently fixing up a car to use during college. It has many rust spots and (of course) I'm trying to rid it of them. I have seen compounds like CLR literally wash rust away and we used toilet cleaner on shower rust lines when everything else couldn't scratch it. I believe both are heavy acids (could be wrong about CLR) and I was wondering: Would such fluids help in my case or make it worse?
Also, Would any heavy alkali, such as Lye, do the job?

Glenn Cherry
- Ohio, U.S.

March 15, 2012

Hi, Glenn.

You shouldn't use CLR, vinegar, or HCl on rust in this application because, although it may initially dissolve the rust, it leaves the steel very active and prone to immediate re-rusting ("flash rusting"). What you want is Rust Converteramazoninfo, also called Naval Jellyamazoninfo, which is based on phosphoric acid and has the capability of converting the dusty, flaky red rust to stable "black rust".

Alkalis like lye are good at dissolving oil and grease, but don't convert rust.


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Ted Mooney, P.E. RET
Brick, New Jersey

May 3, 2012

Q. Hi, I'm in 6th grade, and doing a project about pH and rust.
But I don't understand why baking soda and water doesn't cause rust to form?

Simon H.deleted
- San Ramon, California, USA

May 4, 2012

A. Hi Simon.

Since your project is about pH and rust, what did you find the pH of the baking soda and water to be? Then we can talk about your question and its relationship to your project.


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Ted Mooney, P.E. RET
Brick, New Jersey

pH Paper

May 10, 2012

Well, we didn't have the pH strips, so I just looked it up, and found that the pH is 9, which, according to my experiment, would be rusting, but I did another two, one with less baking soda and one with more baking soda, but still got the same result. So, I don't get it. Please, this is very urgent!!!

Simon Handeleted
- San Ramon, California, USA

May , 2012

Hi again. So, you are asserting that the pH of water with baking soda is 9.0 for all three of your concentrations. That may be true although it sounds high to me.

I'm not sure what you mean by "according to my experiment, would be rusting" -- because, you just finished saying that according to your experiment there was no rusting. Do you maybe mean that the instructions or notes for your experiment suggested that there would be rusting?

I would not expect baking soda to cause more rust than plain water, because alkaline pH (greater than 7.0) tends to retard rust. I'm not sure how deeply you covered pH for your "pH and rust" experiment, but the pH indicates whether there is an excess of H+ or OH- in the solution, and by how much. At pH 7.0 there is an even balance. At pH less than 7.0 there is an excess of H+, the lower the pH, the more H+. At pH over 7.0 there is an excess of OH-, the higher the pH, the higher the OH- concentration.

Usually, low pH solutions, with their excess of H+, will react with iron and dissolve it, whereas high pH solutions, with their excess of OH, do not react with iron.


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Ted Mooney, P.E. RET
Brick, New Jersey

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