What is rust? and how does pH effect this?

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

Thanks

Hi 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 :-)

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
September 2014

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.

A. I'm doing that science fair project too! We used Lemon Juice, Water, and ammonia ⇦this on eBay or Amazon [affil links] , because they have different pH. ammonia has the lowest pH and it rusted the most. Hope this helps!

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.

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.

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

I'm doing a thing on rust too!

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.

Regards,

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 ⇦in bulk on eBay or Amazon [affil links] , 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 ⇦this on eBay or Amazon [affil links] , also called naval jelly ⇦this on eBay or Amazon [affil links] , 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.

Regards,

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.

Regards,

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!!!

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.

Regards,

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.

Regards,

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.

Hi 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.

Regards,

 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 Quora.com, 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.

Regards,