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topic 48959

How does pH affect rust



A discussion started in 2008 but continuing through 2018

June 5, 2008

Q. I'm doing a science project, and I'm doing it on how pH effects rust, I have water (pH 7), bleach (pH 13), and vinegar (pH 4), it is rusting steel wool [linked by editor to product info at Rockler], and I thought the acid will rust it the most, because that is what I researched, but the vinegar destroyed it and the bleach is rusting it tonnes, so what rusts better a base or acid?

Nathan P [last name deleted for privacy by Editor]
student - Australia


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June 5, 2008

A. Hi, Nathan. This question has been asked and answered many times on this site, but the threads grew painfully long, so I guess it's okay to take it from the top again :-)

It might surprise you to know that acids are most commonly used in industry to remove rust, not to eat away steel. Although acids are capable of dissolving metal, they are even much more capable of dissolving rust (that is, the rust will dissolve into an acid much faster than the raw steel will). So vinegar, which is about 5 percent acetic acid in water, will tend to remove rust rather than cause it. But, if the vinegar dries out, the metal that dissolved into it cannot stay dissolved with no acid and water left, so it will become rust. That is why "spritzing" steel with vinegar can make it rust. And if you allow your experiment dish to dry out, it will be a rusty mess.

Bleach is sodium hypochlorite (NaOCl), which releases large quantities of oxygen and chlorine gas as it decomposes. These oxygen and chlorine gases are very powerful oxidizing agents. Rust is oxidized steel, so these oxidizing agents are very good at oxidizing steel into rust. Bleach is very effective at rusting steel, but it is not because of its pH! In fact, the pH of bleach is high because alkali (NaOH) is deliberately added to bleach to slow down this decomposition (bleach wouldn't be as useful if it instantly decomposed). That is also why you are warned never to add other chemicals to bleach. If you add vinegar (acid) to bleach you would lower its pH and the ability of the chlorine gas to stay in solution. So massive (and dangerous) amounts of toxic chlorine gas could be released. People have died from this; be very careful to not mix vinegar and bleach when you do your experiments. Good luck.

Regards,

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


June 6, 2008

A. As dangerous as chlorine gas is, it will also release OCl's which are the basis of several war gases, as is chlorine gas.

James Watts
- Navarre, Florida


August 2, 2008

A. I think Ted's explanation is correct to some extent. Chemistry can give path to think on this subject.
Vinegar which is said to be weak organic acid has lesser dissociation power than that of inorganic acids like HCl, H2SO4, HNO3, which has high ionisation power in solvent like water. So if you want to compare you should use strong acid and strong base like HCl and NaOH, both having equal dissociation approx.
Secondly pH is not the only criteria for rusting. You can test even common salt NaCl, which is neutral pH.
Rusting may be directly proportional to the electrolyte in the solution.

You will get good info about this in ACID AND BASES IN CHEMISTRY.

Sagar Deshpande
- India


December 12, 2009

Q. Hello there fine sir! I have also done an experiment similar to this. My partner and I tested how pH effects the corrosion of regular and galvanized nails. We used 5 liquids (with different pH) but the only ones that seemed to show noticeable corrosion were water and vinegar. This was a bit puzzling because one has a neutral pH and the other is pretty acidic. Can you tell us why these affects came out the way they did?

David F [last name deleted for privacy by Editor]
- Wilmington, Delaware


December 12, 2009

A. Hi, David. You can't give people just a small part of the data and expect them to explain it :-)

What were the other 3 liquids and their pHs? What was your test: immersion? How many hours, days, or weeks? Your question seems to imply that steel nails and galvanized nails reacted exactly the same, which sounds highly unlikely to me. You have to explain what happened before we can explain why it happened; please get back to us.

Regards,

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


January 26, 2010

Q. So pH does affect the level that it rusts or it doesn't. Please answer back. I have a conclusion due by tomorrow and there is nothing on the web that can help me so this is my LAST RESORT! Please help me! PLEASE PLEASE PLEASE WITH CHERRIES ON TOP! :O! Thanks to whoever out there willing to help me! PLEASE HELP!

Eunice S [last name deleted for privacy by Editor]
- Chicago, Illinois


January 2010

A. Hi, Eunice. Yes, pH affects rusting. Steel tends to not rust at high pH, whereas steel rapidly corrodes at low pH.

But how can you write a conclusion without doing the experiment? And if you did the experiment, base your conclusion on it :-)

Regards,

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


February 8, 2010

! Thanks so much! I thought so because my project DID support it but I thought I did the project wrong! I'm going to regionals!

Eunice S.
- Chicago, Illinois


November 30, 2010

Q. Hi. If anyone is out there, I need help.

I have a research report I have to hand in. Right, well, I don't know what types of liquids effect the process of rust "corrosion". If you tell me some of the liquids that are effective that would be great, thanks.

P.S. My spelling sucks. Thanks so much.

james u [last name deleted for privacy by Editor]
- Priddis Alberta Canada


December 1, 2010

A. Hi, James.

Yes indeed, your spelling sucked, and your punctuation and capitalization, too -- but we corrected it. Still, if you take the time to ask well thought-out questions, we'll certainly try to answer anything you are stuck on. However, you seem to be asking us to write your essay for you because you don't want to do an experiment or any research either :-)

I'm not trying to be mean and make science class more unpleasant for you -- but you don't seem to like science, and continuing on your present course you never will. Whereas if you actually do the experiment and study up on it, there is at least a chance you'll start to enjoy it :-)

Start with the first question on this page and the answer we offered, as it seems to cover what you are asking. Good luck.

Regards,

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


January 4, 2011

Q. Hello guys.
I'm doing an experiment now on how acids affect the rate of corrosion. I'm having hard time for now.
I'm using a meat thermometer but it wasn't giving an accurate reading because the only readings can be seen on there is almost about 120° F. but I didn't reach that one.

Can you simply tell me how vinegar affects steel?

e-jhaiye g [last name deleted for privacy by Editor]
- Philippines


January 4, 2011

A. Hi, E-jhaive. You are not really doing an experiment yet. So far, you are simply playing with vinegar and metal and with a thermometer that you know is not useful (and if it's metallic, it's maybe even messing up your reactions).

For example, you don't have a data point for temperature, and rather than getting one when you have realized that you should have it, it looks like you intend to fudge that data point to look plausible. And rather than relying on your experimental data for the effect of vinegar on steel, it looks like you intend to rely on someone else's guess of what might happen ("simply tell me how vinegar affects steel"). Please describe the procedure you used in your experiment, and what results you got, and then we can actually help you with your conclusions. Thanks!

Regards,

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


February 28, 2012

Q. Please help. I am doing an experiment where I put a coiled copper wire and a rusty nail into a glass bowl filled with vinegar. Does vinegar speed up or get rid of rust. Also does it matter if the bowl is not glass or does it change the effects of the experiment.

Tim Dockin
- Miami, Florida, U.S.


February 28, 2012

A. Hi, Tim.

The bowl doesn't actually have to be glass. It can be plastic or china. It just can't be metal: because metal conducts electricity, thereby connecting the nail to the coil of copper wire, allowing electric currents to flow between them, corrupting their independence; and because the vinegar or other ingredients may react with metal. So, after you put the objects into a non-metal bowl, tell us, did vinegar speed up rusting or get rid of rust?

Regards,

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


April 28, 2012

Q. I'm doing an experiment on the effect of pH on the removal of iron rust. My teacher put a note on my paper and asked me to explain why pH would affect rust. I don't know what to say, if you have any tips that would be awesome.

Joshua Lytle
- Palmer, Alaska, USA


May 1, 2012

A. Uhhh, Tim ... you haven't told us "the effect of pH on the removal of iron rust" as determined by your experiment, yet you are asking us to explain why you got those results :-)

What were your results? Please tell us what grade you are in so it can be phrased in proper terms (we don't want to talk way over the heads of third graders, nor speak baby talk to twelfth grade chemistry students). Thanks.

Regards,

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


July 20, 2012

Q. Hi,

I was wondering if you could explain the reasons why the rate of corrosion is increased by lower pH? I've probably got it wrong but I thought that the H+ would react with the OH- ions and slow down the reaction? I have quite limited knowledge on rust and I just thought that you might be able to help me understand it a bit more... I did an experiment that proved that rate of corrosion increases in acidic solutions, but I can't really get my head around why. And it's a small part of a report that I'm doing. Thank you!!

Samara Griffin
- Perth, WA, Australia


July 22, 2012

A. Hi Sam.

If the pH is low (acid), there will be a lot of H+ ions and few OH- ions to neutralize or balance them.

The H+ ions will tend to react with metals, giving up their positive charge, giving it to the metal so the metal can oxidize (have its oxidation state raised) and go into solution.

For example, if the acid is hydrochloric acid, the reaction will look like this:

2H+Cl- + Fe0 => H2^ + Fe++Cl-2

Good luck and Regards,

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


May 28, 2013

Q. Hello,
I have just done an experiment to test which conditions will produce the most rust. I tested this by putting iron nails in HCl, NaOH and NaCl solutions of 10M, 5M and 1M. The results I had was that 10M NaOH produced the most rust, then 10M NaCl, and 10M HCl. But really, I think that's mostly due to errors, since there were residues of solid NaOH and NaCl included when weighing and since the HCl reacted with the nail and no nail were left in the end. Could you please tell me whether my information is correct? And, if not, what is it suppose to be? And why?

Issy Teri
- Chiang Mai, Thailand


May 31, 2013

A. Hi Issy. Steel should not corrode in NaOH whether 1M, 5M or 10M, so your results are indeed hard to understand. I think you must repeat it.
Salt is corrosive, so you should expect some corrosion in 10M NaCl.
When you say 10M HCl produced the least rust, yet the nail completely dissolved, i.e., lost 100% of its weight, you are obviously saying that your interpretation of your experiment is quite wrong.

Here's what I think you were trying to do:
- weigh the dry nail before the experiment - immerse the nail in the solution for a given time - clean off any non-steel stuff, rinse and dry the nail - weigh the nail to see how much mass was lost, i.e., how much corrosion occurred.

Good luck.

Regards,

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


June 5, 2013

Q. Hi I've also done a similar experiment in which I put identical iron nails in 5 different liquids: lemon, vinegar, orange, water and bleach. I have read that the lower the pH the higher the rate of rusting would be. But my result shows that bleach is causing the fastest rusting. Can you please explain this thing for me please? If you can, please try and do so ASAP because it's due tomorrow! :)

Many thanks,

Sam

Sam W [last name deleted for privacy by Editor]
- California, United States


June 5, 2013

A. Hi Sam. I answered this exact question at the top of the page. If you did not understand my explanation, please try to frame your question in terms of what you were not able to follow, and I will be very happy to try again. But if you didn't read the page, you are not yet understanding the "research" portion of science learning :-)

Regards,

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



June 11, 2014

Q. Hi, I did an experiment on rusting iron. I used acid solutions and base solutions. For my bases I used Bi -Carb soda & water, and Sodium hydroxide. My base solutions caused the iron nail to gain weight, but no rust was formed on the nail. It was like the same condition for both solutions. Everywhere I've read it says the bases don't affect the metal, but they caused the nail to gain weight, Why?

Chelsea Scott
- Brisbane, Queensland, Australia


June 2014

A. Hi Chelsea. It doesn't seem correct to me. Are you sure you weren't just measuring wetness or being fooled by poor calibration of your scale? What is the appearance of the nail? Is there anything that resembles some sort of coating?

Is there any chance that the solutions are contaminated with copper or some some tramp metal that is immersion depositing on the less noble iron nails?

Regards,

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



Why doesn't iron react with bases like it does with acids?

September 2, 2014

Q. Hello, I have also completed a practical based on pH levels and rusting. I understand the science behind why acid accelerates rusting, but why do bases not? Is there an equation which could explain this?

Kind regards,
Jack

Jack Stevens
- Melbourne, Victoria, Australia


August 2014

A. Hello Jack. Okay, you understand the reaction of iron with acid; a typical equation for it, as already shown on this page, is:

2H+Cl- + Fe0 => H2^ + Fe++Cl-2

So, here's iron with an alkali/base/caustic:

Na+OH- + Fe0 => ?

The iron is not going to combine with the sodium because neither sodium nor iron can have a reasonable negative oxidation state to accommodate the positive oxidation state of the other. And the iron is not going to grab the OH- ions and cause sodium to be reduced to metallic state because sodium is an extremely active metal that won't do that. In fact, sodium is such an active metal that, if exposed to water, it will burn explosively.

Regards,

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


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