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topic 6997

What is rust? and how does pH effect this?

A discussion started in 2001 but continuing through 2018


Q. 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 A [last name deleted for privacy by Editor]
- Morton Grove, Illinois


A. 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

September 2014

thumbs up signHi Ajit. Thanks for helping make this thread a good source of information for all readers. For 8th-graders like Alison, though, I think college level chemistry books may be impenetrable :-)


Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


A. 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 a long 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 P [last name deleted for privacy by Editor]
- U.S.S.R.


thumbs up signI have no doubt that you've given us 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 bucking 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 actually be in Jax, Florida. Please be careful on the internet because you are not as anonymous as you think.

Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


Q. 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!

Leah [last name deleted for privacy by Editor]
- Chalfont, Pennsylvania

sidebar (2003)

!! 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 [last name deleted for privacy by Editor]
future Doctor and Newswoman - Louisville, Kentucky


thumbs up signPeople 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!

Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, 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 [last name deleted for privacy by Editor]
student - Houston, Texas

Earth Science for Every Kid
from Abe Books


Kids Guide to Research
from Abe Books



Q. 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 [last name deleted for privacy by Editor]
- Calgary, Alberta, Canada


A. 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 [last name deleted for privacy by Editor]
- Taylor, Missouri


Q. 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 T [last name deleted for privacy by Editor]
Science and Technology - Butuan City, Philippines


A. 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 rust, it 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 longer ... it is not just because the metal is wet. Hope that helps.

R.G. [last name deleted for privacy by Editor]
- Port Hueneme, California


A. 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 metal and contaminates (electrically connected and carried by the electrolyte). The loss of metal atoms in the reaction causes rust.

R.G. [returning]
- Port Hueneme, California


Q. 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 F [last name deleted for privacy by Editor]
- Austin, Texas


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

Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

April 19, 2008

thumbs up signI'm doing a thing on rust too!

Emily S [last name deleted for privacy by Editor]
Student - Ottawa, Ontario, Canada

May 7, 2008

Q. 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 [last name deleted for privacy by Editor]

9th grade student - Hamer, Idaho

July 23, 2008

Q. 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 [last name deleted for privacy by Editor]
- Russellton, Pennsylvania

A. 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 positively charged particles (atoms from which one or more electrons have been removed, 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.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

January 4, 2009

Q. 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 S [last name deleted for privacy by Editor]
- San Francisco, California

January 5, 2009

A. 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 high chloride content and the way it generates nascent oxygen. In general, a high pH will tend to slow down or stop rust rather than accelerate it like bleach does. 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; 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. Acid dissolves metal, but it dissolves rust even faster. In industry, acid is used as a rust remover.

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. Also, the acid can eventually become exhausted from dissolving all the iron it can hold, then it will turn rusty.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

January 22, 2009

thumbs up signHey,
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 B [last name deleted for privacy by Editor]
- Louisville, Kentucky

February 27, 2009

thumbs up signlol. I'm in 5th grade and I'm doing it as well. This info given is very explanatory.

Oliver C [last name deleted for privacy by Editor]
- Singapore

March 14, 2010

Q. 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 Y [last name deleted for privacy by Editor]
- Sydney, NSW, Australia

November 9, 2010

Q. 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 N [last name deleted for privacy by Editor]
- Jax, Florida

February 8, 2011

Q. 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 J [last name deleted for privacy by Editor]
- Santa Rosa, California

February 8, 2011

A. Hi, Victor

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

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


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

June 7, 2011

Q. 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

A. 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 really don't think they are.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

sidebar March 14, 2012

Q. 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

A. Hi, Glenn.

You shouldn't use CLR, vinegar, or HCl on rust for that application because, although it initially dissolves the rust, it leaves the steel very active and prone to immediate re-rusting ("flash rusting"). What you want is Rust Converter [linked by editor to product info at Amazon], also called Naval Jelly [linked by editor to product info at Amazon], 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.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, 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. [last name deleted for privacy by Editor]
- San Ramon, California, USA

pH Paper

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.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

May 10, 2012

Q. 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 H [returning]
San Ramon, California, USA

May , 2012

A. Hi again Simon. 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. Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

September 28, 2014

Q. I'm a college student in an energy class and I'm wondering if an iron pipe will tend to rust if stored in soil with pH=6?
I think it will...

Holly Lacey
student - College Park, Maryland, USA

September 2014

thumbs up sign Hi Holly. I also think it will tend to corrode or rust. But this thread talks about testing and research, and it may be better to employ one or both of those ideas than to guess. Best of luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

September 29, 2014

A. In my area of Florida, you cannot run natural gas to a house in galvanized pipe. You can use black pipe. I think that the reason for this is some galvanized pipe is seam welded and fails with time in some soils. Nearly all of the "gas" companies now use fusion welded plastic pipe which makes it virtually a continuous pipe.

James Watts
- Navarre, Florida

January 13, 2016

Q. Hi I'm a high school student and I'm doing how pH values affect iron rusting rate. I used the pH3 to pH11 solution to do this lab but my result was not very accurate. I'm not sure if my idea is correct but I thought the more acidic acid rust more quickly than the pH6, pH7 solution. And pH11 solution rust quick as well. Is that true?

Celia Wang
- Ottawa,Canada

January 2016

thumbs up signHi Celia. One of the world's most respected teachers, nuclear/quantum scientist Richard Feynmann, said:

Richard Feynmann

"It doesn't matter how beautiful your theory is, it doesn't matter how smart you are. If it doesn't agree with experiment, it's wrong."

The most important lesson you should be learning from your science class is how to properly conduct an experiment. If your "result was not very accurate", you should be focusing on re-doing the experiment so that your results are trustable.

A. In general, low pH corrodes iron faster than high pH but, as previously explained, low pH also dissolves rust even better than it dissolves iron. So you can't use visible rusting as a measure of how fast or how much the iron is corroding. Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

Metal Samples

June 4, 2016

Q. I'm in grade 8 as well and I'm researching the effects of higher or lower pH levels and how it effects the speed of corrosion. I'm just wondering if you have any suggestions for types of metals and liquids that I could use for an experiment?


Ethan Waller
- Australia, Queensland

June 14, 2018

thumbsdown Firstly I would like to refute Sam F's response on this thread in his saying that is was his own research. That response was copied & pasted from the "DOE FUNDAMENTALS HANDBOOK - chemistry", U.S. Department of Energy, 1993. I am requesting his response be removed from the thread.

Q. Now, I personally have conducted my own experiments involving the corrosion rates of solutions with varying pH levels (4-9) using solutions of water, salt and an acid (HCl) and base (NaOH) and found no relationship between pH and corrosion rates which did not support my hypothesis. Research led me to many many conclusions varying from ion concentrations, dissolving of rust in acidic solutions (which was found in the above mentioned handbook) and the substitution of water for hydrogen ions within the initial RedOx reaction for rust. I am seeking clarity from any expert on this topic as to what is the definitive relationship between pH and corrosion as well as an in-depth description of WHY there is a relationship.

a very confused student

Markus Ayma
- Brisbane, Queensland, Australia

June 2018

thumbs up sign Hi Markus. Thanks! Sorry, I don't have easy access to the book you cite, so if you have time, please photograph that paragraph and e-mail it to us.

If I were Sam's teacher I would be very concerned about possible plagiarism. But I'm not, and I see the same paragraph quoted without attribution several other places on the web, including at, but with dates long after Sam F's posting. So who knows whether Quora and others copied from this page or from the book or from some other source? Because it's only one paragraph, it's probably 'fair use' anyway, and something that happens on the web all the time (our chrome plating article has been copied without attribution on more than a dozen sites). So we've printed your claim as to its source, and your admonition of Sam, but I see no value in removing the paragraph.

A. In response to your question, low pH means a lot of acid (H+ Cl-) in solution. Iron is a cation like H and competes with it to combine with the Cl into iron salts. Two H ions then combine to form H2 gas and evolve from the solution, making the reaction one directional. At higher pH, the iron cannot successfully compete with the Na in NaOH because Na is such an active metal, so no substantial corrosion occurs.

But there is a lot to it! Reactions occur faster at higher temperatures, reactions occur slower as solutions become saturated, common ion effects and precipitation have some effect on speed. If the metal wasn't spotlessly clean, organic contamination can slow the reaction; in fact there are proprietary chemicals sold as "inhibitors" designed to prevent the acid from attacking the raw iron, and other proprietaries sold as "acid extenders" designed to make the dissolved iron precipitate.

If you'd like to look deeply into the reaction rate of iron with acids, especially HCl, please search for "Kleingarn reaction". Our on-line library includes a very interesting article on that topic, generously provided by Barlow R. Campano.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
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