How does pH affect rust

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,

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.

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.

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,

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,

! 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!

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,

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,

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,

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,

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:

Good luck and Regards,

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,

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,

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,

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,