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topic 48959, p2

How does pH affect rust



1       2



A discussion started in 2008 but continuing through 2018

November 23, 2014

Q. I'm trying to help my son with this project. We put 3 small pcs of steel I-beams into 3 different plastic containers.
First we had 50% ammonia 50 % water,
second we had 100% water,
and the third we had 50% battery acid with 50% water.

After two weeks the first container had a very little rust color the second was very rusty and the third had no rust at all. We didn't measure the weight of the steel pcs. I'm not sure how to explain the amount of corrosion. The most corroded steel has no sign of rust! Please give us a hint!

Stephen Domonkos
- Bay Shore, New York, USA


December 2014

A. Hi, Stephen. It's actually not complicated, just a little anti-intuitive: acid attacks rust more readily than it attacks solid metal. So as long as the acid has acidity available to dissolve steel, it has acidity available to dissolve rust. Acid is widely used in industry to remove rust, and only rarely to dissolve steel.

The iron is indeed dissolved in that acid, but you won't see it come out as rust until the acid is exhausted or evaporated.

On the other hand, water does not dissolve rust, so the oxygen in the water and air combines with the steel to form iron oxides (rust). Ammonia is a mild alkali, and alkalis tend to reduce the corrosion of steel, so it probably doesn't rust as quickly as in pure water. Good luck.

Regards,

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



December 12, 2014

Q. Hello, my son has completed his science project. The project is which liquid corrodes steel nails the most...

He placed the nails in water, salt water, lemon juice, and Coke for 14 days. The water and salt water lost the most mass -- the other two liquids weighed the same as day 1. I have read the comments but did not see, or missed, comments on well water. We used well water with a pH of 7.8- could this be why it lost more mass than the acidic lemon juice? We did not take this into account at the beginning. Thanks

melissa corley
parent 6th grade science project - usa


December 2014

Hi Melissa. Well water is not much different from "city water". Both are drinkable, and monitored for other ingredients; "city water" can come from a number of places, including wells.

"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."
    -- Richard Feynmann, dec., Nuclear Physicist (and considered by some to be the world's greatest teacher)

Although your son's results sound unlikely, they are his results -- and the point of a science experiment is to record the results you actually got, not what you expected to get. Most likely either 1). something was recorded wrong, or 2). your weighing procedure doesn't actually measure the mass lost to corrosion correctly, or 3). the weighing equipment isn't precise enough and leads to measurement variations that are random rather than causal. Or maybe 4). water corrodes steel nails more than lemon juice or coke.

But my guess is that it may be "2)." Rust and other corrosion products weigh more than the iron from whence they came because the corrosion products have all the original iron plus oxygen or whatever is in the corrosion compounds. If your procedure weighs the corrosion products attached to the nail, rather than just the uncorroded iron, you can get this sort of result. So how do you determine the amount of mass lost? Did you clean the nails with sandpaper or in any other way after their exposure to the corroding medium so that you were weighing just the remaining un-corroded steel? Good luck.

Regards,

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


sidebar July 13, 2015

thumbs up signI don't have a question but I have to say this after reading how you replied to the others. I have to say the way you put time to answering questions like this is awesome. Thank you.

Caleb Huntington
- Morayfield Queensland Australia


October 14, 2015

I agree with Caleb Huntington, even though I've only been looking at the thread for help on my own project for a couple of hours now. I'm very (and weirdly) sentimental about things and the fact that you've kept up with responding to these questions for many years now astonished me, and also how quickly and efficiently you've answered them. You're doing a fantastic job Mr. Mooney, keep up the good work.

*p.s. these things just interest me, and have a good day sir.

Christopher T.
- Carrollton, Georgia


Hi Caleb. Hi Christopher. Thanks so much for taking the time to send along your kind words!

Regards,

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



November 29, 2015

Q. I thought that because of vinegar's low pH level it would rust my steel wool the most, but as I was observing the steel wool in bleach and Hydrogen Peroxide it had noticeably more rust. Though my temperature recordings show that the vinegar produced the most chemical change, this makes me certain that the steel wool should have the most rust after an hour. The steel wool is still in the vinegar. What am I failing to do?

Carolina Herrera
- Chicago, Illinois, USA


December 2015

A. Hi Carolina. We're not there to look over your shoulder, so you have to be careful explaining yourself or you can quickly lose us. But it seems that you are you wondering why you are not seeing rust in the steel wool in vinegar? Please see my first answer on this page: Vinegar, like other acids, dissolves the iron in rust even more readily than it dissolves the iron from steel wool. You won't get rust as long as the solution is still acid, but the acid will eventually start dissolving the steel wool. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



January 13, 2016

Q. So I was wondering about the affect on steel wool and pH levels?
So basically I have vinegar, lemon juice, orange juice, black coffee, and water. I don't have these supplies however I need to know how long each one takes to make steel wool completely corroded. Thanks in advance!

Ritvik D
- Herndon, Virginia, USA


January 2016

Hi Ritvik. Sounds like a fascinating science project: ask a stranger to guess the result of an experiment you don't feel like doing :-)

A. I'd say one minute for vinegar, 2 hours for lemon juice, 3 days for orange juice, 4 weeks for black coffee, 5 months for water. I'm pretty sure I'm right.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


October 9, 2016

Q. Hello, I have done an experiment immersing different type of metals (paper clip, thumbtack, one sen coin, can top and stapler pin) in a different solutions (vinegar, detergent water, oil, and tap water). And the experiment was conducted for 30 days. It has been observed that the tap water changes from colourless to blue solutions when a coin is immersed in it. Can I know why the solution turned blue?

Thivina Jayaraman
- malaysia, seremban, negeri sembilan


October 2016

A. Hi Thivina. Copper ions (Cu++) tend to be blue. I'd say some copper from the coin dissolved into the tap water, which is probably slightly acidic. What happened to the copper coin in the vinegar?

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



March 3, 2017

Q. Hello. I have a science fair coming up. I'm doing it on does pH effect the speed of rust? I don't understand how pH effects the speed of rust.

Ellis Guo
- Markham, Ontario, Canada


March 2017

A. Hi Ellis. As asked earlier on this page, please tell us what grade you are in because the explanations needs to be very different for 3rd graders vs. seniors in high school. Try to read some of the answers on this page and tell us what you understand and don't understand. Are you 100% sure that you know exactly what you mean by "pH" and by "speed of rust"? It wouldn't make any sense to try to provide an answer if you don't understand the question. Good luck; we'll be here.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


March 29, 2017

thumbs up sign As a high school (homeschool) chemistry teacher, I really appreciate your posts, especially your recommendation to read the entire posts (i.e., do your research), present all your data and explain your results--what you observed, not what you should have seen. This is how I want my kids to learn and approach science. Thank you for such a great resource!

Nancy Lawless
- Gaithersburg, md


May 2017

Thank you for the kind words, Nancy :-)

I would never have the patience to be a teacher :-)

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



September 18, 2017

Q. I'm somewhat confused by the first response, so please forgive any misunderstanding.

I work at a paint and coatings company, and am told higher pH coatings will cause steel substrate to rust less than if the coating were lower pH.

If I understand the explanation here, low pH, at least acetic acid, causes oxidized iron *already present* to dissolve and when dried will 'agglomerate' on the substrate giving the appearance of rusting?

Please correct that understanding. Also am curious if there is any validity to the claim higher pH paints rust less than the same paint with lower pH (using amines).

Thanks for any reply.

Rick Moore
- Chicago, Illinois, USA


September 2017

A. Hi Rick. I was answering a question about a student science project, and I can't claim expertise in paint formulation :-)

Students wonder why they see less rust in acidic solutions than in neutral or alkaline solutions despite the acidic solutions being more corrosive, and the answer is simply that acids dissolve rust as readily as raw metal, in fact more readily.

But, yes, I would expect a high pH paint to deter rusting more effectively than a low pH paint.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


September 26, 2017

Q. Hi
I just wanted to know how does the pH of a liquid remove the rust. I need to know because I have to write the answer to this question in my report and I can't find the answer anywhere.

So please can you answer this question with the most detail and why low pH removes rust.

Edward James
- america, La


September 2017

A. Hello Edgar Z from Stockholm, Sweden. On the internet you are not as anonymous as you think, so be careful out there.

wikipedia
Rust

Per Wikipedia, rusts are hydrated iron oxide and hydroxide compounds like
Fe+++2O--3, Fe+++O--(OH)-, and Fe+++(OH)-3,

whereas acids are compounds like
H+Cl-, H+2SO4--, and (CH3COO)-H+

When one of the forms of rust, for example, Fe+++2O--3 reacts with one of the acids, for example, H+Cl-, the formulas are of the form:
Fe+++2O--3 + 6H+Cl- => 2Fe+++Cl-3 + 3H-2O--

In the given example, the iron from the rust becomes dissolved in the solution as ferric chloride. The H+ from the acid is what makes this dissolution possible, and pH is a measure of the available H+, the lower the pH the more H+. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



October 19, 2017

Q. Hi,
I am in 9th grade and I'm doing an experiment on .. The Effect of the pH level of a solution on the rate of corrosion. My levels of IV is lemon juice, saltwater, distilled water, black coffee, and orange juice. I'm sorta stuck on how to execute the experiment since I will be using the corrosion formula to measure the rate of corrosion. This is what I have :The corrosion rate formula is 87.6 x (W/DAT). Where W is the weight loss in milligrams, D is the steel wool density in g/cm^3, A is the area of steel wool in cm^2, and T is the time of exposure of steel wool in hours.
I would like to know how to execute my experiment.
Thank you!

Anu B.
- Chantilly, Virginia


October 2017

A. Hi Anu. What do you mean by "My levels of IV..."? Sorry, that means nothing to me.

The formula which you mention predicts how many millimeters of thickness a plate will lose to corrosion in a year based on the results of a short term experiment, but I think you would find this formula difficult to implement at best because there's probably not a practical way to determine either the area or the density of your steel wool, being comprised as it is of thousands of very small diameter wires and a lot of air space. More practical would be to just use the same amount (the same weight) of steel wool for each of your liquids, and just plot weight loss to corrosion vs. pH.

So you measure the pH of your 5 liquids, weigh the chunks of steel wool before immersion, and weigh them again after you take them back out of the corrosive solutions. There are, of course, other practical difficulties with this experiment: other things besides pH may affect the corrosion rate; and I don't know how you're actually going to remove the adhering corrosion products from the steel wool after immersion so that you can weigh how much raw steel you have left. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



November 17, 2017

Q. Hi,
I am researching how salts in hard water (coolants) tend to corrode the material being machined (the work piece). Ions like chloride, sulfates, sodium in sulfate tend to corrode the work piece, whereas phosphates, carbonates, bicarbonates tend to increase the alkalinity of the coolant. Could you explain this?
Regards

nithin reddy
- hyderabad, india



December 12, 2017

Q. Hello, I am doing a science project for my 8th grade science fair. The project involves immersing steel wool in liquids with different pH levels, and all liquids but the pure water I am using are acidic. I am trying to test whether or not the speed at which rust forms on the steel is affected by how low or high the pH level is, and am comparing this rate with the speed at which rust forms when affected by "normal" water, with a pH of 7. I have read this whole thread to the end (I am surprised by its consistency through several years) and don't understand the reason why iron would corrode faster in the presence of substances with a lower pH. Why does the acidity cause iron oxide to form faster? What is the acidic substance doing to the steel to make a it react this way? Sorry for the long question, I wanted to sum up some of the questions from this thread so others with the same problem don't have to go look. Sorry if I'm simply being unintelligent and there is a simple answer to this question; I am just stuck and can't find other sources on the internet.

Thanks, Albert

Albert H [last name deleted for privacy by Editor]
- San Francisco, California United States


December 2017

A. Hi Albert. Good luck with it.

pH is a measure of acidity, the lower the pH the more acidic. And what that really means is the lower the pH or the more acidic the acid is, the more hydrogen ions available to dissolve metal. Hydrochloric acid is a very strong acid which we abbreviate as HCl; using HCl as the example because it's easy to write, it spontaneously separates or 'ionizes' to H+ and Cl-: positively charged hydrogen ions and negatively charged chlorine ions.

Steel wool is primarily made of the element iron, which we abbreviate as Fe. If you put steel wool into hydrochloric acid, the positively charged hydrogen ions are searching strongly for electrons to balance them and they have a stronger pull on the electrons than iron does. So they will 'steal' an electron from the iron they touch, converting it from Fe0 to Fe+, or two hydrogen ions may between them steal 2 electrons converting the iron to Fe++, or 3 hydrogen ions might steal 3 electrons and convert it to Fe+++. Exactly which form the iron goes to depends on some other stuff and is beyond 8th grade science, but in any case this converts the Fe atoms into positively charged Fe ions which dissolve into the solution and combine with the chlorine atoms to form somewhat soluble salts like FeCl3. That's how acid dissolves metal, but it's also what it does to rust (Fe2O3). So you don't immediately see more rust with stronger acids, you see less because the iron in the rust as well as the iron in the object gets ionized into soluble salts like FeCl3.

So a point I have been trying to make is that acid attacks and corrodes steel, but generally this is not seen as rust because the acid dissolves rust even more readily than it dissolves steel.

What you could do is try to dissolve the steel wool in pyrex bowls of acids for a fixed amount of time, say 2 days, then dry the bowls of liquid and steel wool in a warm oven so the ferric salts cannot remain dissolved; the lower the pH, the more rust you might now see.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


December 12, 2017

Thank you, I've never once seen a site that automagically has answers for my questions like this, and I'm super grateful! I managed to come up with a hypothesis; I may need to analyze your answer and research some more to make it more accurate. My hypothesis is:

"If iron is affected by acidic substances, it will corrode at a higher rate than it would when influenced by pure water, because substances with a high acidity (a pH lower than 7) have more hydrogen ions available to dissolve metal than pure water (which has a pH of 7)."

If this is not accurate information and I misinterpreted/misread the answer, I'll rewrite. Thanks so much.

Aloha,
Albert

Albert H [returning]
- San Francisco, California United States


December 2017

thumbs up sign Aloha Albert. I'm not sure that 'affected' and 'influenced' are exactly the best words, but this is science class not English class, and I think your hypothesis is perfect! Thanks for the kind words.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



February 7, 2018

Q. Hi, I performed an experiment to determine which solution corrodes steel wool the most in 5 days. I submerged the wool in the liquid for 5 days and measured the overall weight loss. I found that vinegar (acid) corroded it the most, whereas the ammonia (base) had no effect. I am currently In 9th grade but I can't find the reason ammonia didn't affect it. Please explain my results, all the other websites had really complicated answers.

Thank You,

Katie R [last name deleted for privacy by Editor]
- Seattle, Washington, The United States of America


Richard Feynman (dec.), one of the world's greatest teachers:
February 2018

A. Hi Katie. Lots of things will not corrode steel wool, including most liquids which don't contain water, like oils & alcohols, and most liquids which do contain water but are alkaline (high pH) like bicarbonate of soda, sodium hydroxide, calcium hydroxide, and, yes, ammonia (with its pH of about 11). The question is not quite "why doesn't ammonia corrode steel wool?", because who says it should really? The better question is why did those other substances corrode steel wool.

Vinegar corroded the steel wool because it is acetic acid, and acids (low pH) are materials which will dissolve metal because they contain hydrogen in an active form which is hungry to steal electrons from metals when it has the opportunity. When hydrogen succeeds in stealing those electrons (with their negative charges) from the metal, the atom of metal stops being a neutral atom of metal, and becomes a positively charged ion which dissolves into the watery solution as a metal 'salt'.

The best known salt is sodium chloride (NaCl), which is table salt and the most prevalent of the salts in the ocean. One theoretical, although impractical, way of making table salt would be to put sodium metal (Na) into hydrochloric acid (HCl); the hydrogen in the HCl would steal an electron from the Na metal, which would produce free hydrogen gas plus NaCl metallic salt. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



February 16, 2018

Q. Hi Ted
I wanted to thank you for keeping up with all of these questions.
I'm a chef by trade and hobbyist machinist .
I have been experimenting to come up with a clean biodegradable cutting fluid that has water and does not cause Rust.
Especially machining equipment is very expensive; rust will destroy them quickly.

I mixed 1/3 cup of tap water + 2 cups of vegetable oil + xanthum gum to emulsify the solution.
Tested the mixture on a piece if scrap metal, and it started to rust.
So I added baking soda to raise the pH make it more alkaline.
Metal did not rust.

I intend to replicate my experiment each time I need more fluid. My question is, does this make sense chemically or I just got lucky ?
Thanks in advance.

Giovanni Bouderbala
Chef - Salt Lake City, Utah, USA


February 2018

A. Hi Giovanni -- interesting idea. I am not a chef nor a machinist nor a chemist, so I can't comment on the practicality of this mix, but I would agree that baking soda reduces the pH and thereby discourages rusting. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



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