To rust and trust -- school science experiments with rust

A. Hi Ari, interesting results! J Maywald on thread 13329 and Ron Beckett on thread 0139 say that molasses is a slow but remarkable rust remover; I don't know why either, offhand, although it apparently keeps fermenting and keeps producing citric and lactic acids in the process -- a good thing to research further.

I don't think the size of the rusty object matters except ...
remember that this is a chemical reaction between your source of acid and the rust, so acid is consumed in the process and with a big enough item and a small enough quantity of acid, the acid might start getting exhausted.
Good work.


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

A. Given this is for a science experiment, I would suggest you look at the cleaning/rust removing agents you used and consider what the active reagent is in them.
Another interesting angle to look at would be to do a time based analysis.

If you consider what it is you are doing by removing the rust, you are dissolving it (at least in the acids). After the rust is removed you have fresh metal to oxidize then dissolve. You may find that the vinegar, and coke both dissolve the rust quickly but then start to attack the base metal, i.e., creating more rust.

Another point, you will find that screws will have more rust than a wrench per unit mass. Rust is essentially a surface effect so more surface area will mean more rust, all other things being equal.

A. This sounds like a well done project, Marilyn. I think, however, that there is an assumption in the way you are phrasing your question that is a problem and is causing you difficulty. You are assuming that the amount of corrosion and the amount of visible rust are one and the same thing (or at least you are using those terms interchangeably). That is not true, and it probably explains your results.

The problem is that it is possible for iron to corrode, and to dissolve into the liquids in question without forming visible rust. In fact, low pH liquids like hydrochloric acid (pH less that 1) are used in industry to remove rust because they dissolve rust faster than they dissolve metal -- with the result that the metal that started out rusty comes out of the acid rust-free even though the iron can dissolve into this very corrosive acid.

So I think your old hypothesis was proven wrong and your new hypothesis could be that water will cause "more and quicker visible rusting" than the other liquids (but not necessarily more corrosion). An alternate hypothesis might be that low pH liquids cause more corrosion (but not more rusting). That is a good hypothesis but may be difficult to prove or disprove unless your school has a very sensitive scale called an analytical balance [on eBay or Amazon] (the most accurate ones are enclosed in lucite boxes so breezes or breathing on them don't disturb the readings) to measure how much metal has been dissolved away. If you have the money and a strong interest, you can buy a quite accurate electronic pocket scale, measure the weight of the nail before the experiment, and after wiping any rust off after the experiment, and see if you can determine how much iron corroded away. Good luck forward.

A. Close but not exactly, Marilyn. The nail is iron. When iron reacts with oxygen in the air or in water it forms an iron oxide which is visible brown rust. But the iron can also react with an acid like vinegar or lemon juice and dissolve into the liquid, like salt is dissolved in sea water; in this case the dissolved iron may not be visible and obvious. The acid will actually dissolve rust (iron oxide), effectively stopping you from seeing the corrosion as a brown corrosion product. Either way the iron is corroding, but in one case the corrosion products are very visible as brown rust and in the other case they are less visible as a dissolved salt in the liquid.

Based on your findings, again I think your hypothesis is that water will cause more visible rust on a nail than vinegar or lemon juice (but that is not the same thing as saying that plain water is more corrosive). I think you'd find the vinegar and lemon juice caused more corrosion than water, even though it's not visible as rust. This you could determine by weighing the nail before the experiment and weighing it again afterwards. Good luck.

A. Hi again. Your assignment may be to "answer all the questions", Marilyn -- but that's not our job or our goal. My goal is to try to assist in a way that will help make your quiet contemplation be most productive :-)

Again I'll say that you have done a great job on your project so far. Tell your mom that pH and 'how much acid' are pretty much the same thing. The lower the pH, the more acid a liquid is. So, if your pH readings were correct, the lemon juice is the most acid, orange juice the second most, vinegar the third most acid, and water the least acid.

The thing to do now is to restrict your conclusions to what you actually learned, and to separate your conjectures from your conclusions. You have learned that the nails in the water rusted fastest, and the nails in the vinegar rusted second fastest. And the nails in the orange juice and lemon juice did not rust. Those are valid conclusions. It is only a conjecture, though, that if the test were run for a longer time that the nails in either the lemon juice or orange juice would rust at all, and it's only a conjecture that the nails in the orange juice will rust next and the lemon juice will rust last. It's okay to make those conjectures (guesses, hypotheses), but don't confuse them with actual experimental results!

Finally, be careful that words you have been using interchangeably as synonyms are not really synonyms. Your experiment measured, by eye, the appearance of visible brown rust; it did not measure the amount of corrosion. And the fact that you saw no rust in two liquids does not mean that there has been "no physical/chemical change" in the nails, it only means there was no visible brown rust. It is possible that some physical/chemical change occurred that you have not monitored; that is not faulting your excellent work, it's just saying that a 7th grader observing rust by eye cannot really make quite so strong a statement as that.

Your bar graph could show pH of the four liquids versus days until rusting occurred. The "days until rusting" for two of the bars would read "no rust observed in xx days".

A. You are right in saying the lower the pH the more acid is present, and this explains your observations. "Rust", as you are considering it, is a complex mixture of insoluble iron oxides and hydroxides - it is usually brown or grey/black/brown in colour.

However, because you don't see this in an acidic solution doesn't mean the nail hasn't been attacked. Since there is so much acid present, the acid will react with the iron and rust to form a soluble salt, so you won't see it as a solid lump of crud. One thing you may want to do is to repeat the experiment but weigh the nails very accurately before you start and at certain times during the experiment. Make sure the nails are dry before you reweigh them!. You will see a weight loss with time, and this is corrosion, although it is not necessarily "rusting". Rusting is only one form of corrosion.

Your comments about orange and lemon juice are interesting - are they real fruit juices or stuff you got out of a cheap supermarket bottle? If they are the real things, these contain both citric acid and ascorbic acid (vitamin C). Citric acid is a mildly strong acid and can be used under some conditions to protect metals, especially stainless steels. However, ascorbic acid is a much weaker acid and is a mild reducing agent, so it too may offer some protection to the nail. For good rusting corrosion you need lots of air or preferably oxygen, so perhaps you have prevented the air getting to the nail. I like the effort you have put into the work and the degree of interest it has generated in you. I hope you get the rewards you deserve for all your effort.

I would like for you to find out, too, Collin. Do you have a galvanized nail immersed in the coca cola yet? :-)

The first lesson to be learned from a science project, no matter what grade you are in, is that you must never try to bend the experiment to get the results you are "supposed" to get. Instead you must record your actual results first and then attempt to explain those actual results.

A. Ack! Unfortunately you may fail if you are not more careful to express yourself more clearly than you have done so far, Tawney :-)
You have not told us what the chain letter said, nor what was said in the contradictory evidence you came up with. No one but a mind reader can help you know whether the facts claimed in the chain letter are true based on what you have told us so far :-)

Please tell us what the chain letter said, and what your other research said. Most importantly, tell us what happened when you tried to dissolve a nail with Coke. Thanks.

A. You have formulated your hypothesis, Eric, and now you must conduct an experiment to support it or refute it.

Never ask what answer you are supposed to get from the experiment before you do the experiment! That is called "junk science"! Junk science means deciding what you would like the answer to be, or what result would make you feel good, and then you keep redoing the experiment, dismissing the results you don't like, and phonying up the experiment and making it wackier until you finally get a result you wanted in the first place. It's a curse and I would hope your science teacher would never let his/her students get away with it.

Put your nails in vinegar, lemon juice, and soda and carefully record your results. After the results have been RECORDED IN WRITING you then can go back and try to explain them. Get back to us after you have recorded at least some results in writing. Good luck.

A. Well, Kryska, give us your hypothesis and your experimental observations and we'll be happy to help you with your conclusion. A conclusion without these is as silly as trying to top off a Christmas tree with a star or an angel before you have the tree :-)

Neither Christmas tree toppers nor conclusions can just hang up in the air with nothing supporting them.

A. Hi, Abbey. Acid dissolves metal but it also dissolves rust -- in fact, rust dissolves faster and easier in acid than the raw metal does. So acid is often used to remove rust from metal. Is that clearer? If you weigh the nails before and after immersion in acid you will find that they are lighter after immersion because the acid dissolved some of the metal.

If you dip a nail in vinegar or lemon juice for a few minutes it will remove rust. If you leave a nail in it for weeks it will probably eventually come out rusted because iron will keep dissolving until the solution is completely saturated with iron, and the iron cannot stay dissolved anymore as the acid and water evaporate.

A. Please tell us your hypothesis, your experimental procedure, your results, and your conclusion, Logan. Then someone can comment on it. To tell you what the result should be before you do the experiment would be to encourage you to practice 'junk science', and that would likely get you an 'F'. Has your teacher told you the point of this experiment? Have you been told or found out what bleach is and what coca-cola is? Good luck.

A. We've given the reason for that several times just on this one page, Mary. I'll be more than happy to try again if you are having difficulty understanding it, but your question may be reflecting the attitude "just give me the answer" :-)

So, try to express your question in terms of what we've already said about it, and then I will be happy to try to reword it so you get it. Thanks.

A. Steel wool has far greater surface area than a nail, Victoria, so it will react much faster and is probably better if you are going to judge visible rust. I would use just a little steel wool in each jar because you don't want so much that the liquid becomes saturated or "exhausted". I'd probably weigh equal amounts of steel wool to put in each jar. The steel wool will both gain weight as rust starts agglomerating on it, and lose weight as the steel dissolves and as rust flakes off. So I think you'd have a hard time making a quantitative measurement. But if one of the three pieces rusts really badly you could pour the remains through a colander or tea strainer and say that it dissolved so much that it passed through. I think if you started with soap-free steel wool [on eBay or Amazon] from the furniture refinishing section of a store rather than Brillo pads, it should rust really quickly (a few days). Good luck.

A. Rusting is an electrochemical process, Victoria, so the process can proceed faster when the liquid is a better electrical conductor, and saltwater is a better electrical conductor that plain water because the salt ions dissolved in it can carry electrical charges from one place to another. Acids cause corrosion or dissolving of the steel, but they generally don't cause rusting (while still immersed) because acids dissolves rust faster than they dissolve the metal.

A. It is good that you made the observation that Coke turns gooey and Sprite gets yellow, and wrote it down, Madelyn. But those observations do not address the question. You were asked which of the three cause nails to rust, and apparently your answer is: only water.

You will not find research on exactly your question. No real research is done on it because it's just not important: people don't dissolve nails into Coke or Sprite in real life (outside of grammar school science projects). But you will find that acid dissolves rust (because that's important in real life) and that soft drinks contain a mild acid. Then you have to put two and two together. But I think you'll make faster and much better progress with your librarian's help than on the web. Good luck.

A. Even if someone knows about it, if you're doing a science project you should try it yourself, I have recently done a science project and posted it- it's above yours, anyway don't ask about it ... you should try it and see how long it takes. If you don't have enough time to finish your project take what you have and use that, but keep the project going.

P.S. if you really want to know look it up more (likely in library I found lots of information there).

Thanks, Madelyn. Your advice to turn in what you have but keep the experiment going sounds very good, and I agree that a library is a great source for the research.

A. I am amazed that they didn't rust in a month. Are you sure they are not stainless steel nails? Assuming they are not stainless steel, use very clean sandpaper on them while wearing gloves to avoid finger oils to give them a clean, raw finish and they will rust within a day or so.

A. Hi, Trent. When doing science there's nothing wrong with using what you already know when forming your hypothesis. You eat with stainless steel flatware every day. Your parents don't buy new flatware every few days, do they? Do you really think it rapidly rusts when exposed to water? So don't be surprised that your hypothesis that it will rapidly rust was proven wrong. The rust probably came from the steel wool, so it rubbed right off the foil and the spoon.

Regards,

A. Hi, Michelle. It would be best if your school had an analytical balance. This is a very precision scale that even has a glass door on it to keep dust & breezes from affecting the weight. But if you have the money and enjoy the subject, you can get very accurate pocket scale on line for under $25 ⇨

I think you misunderstood your teacher; I don't think you can measure rusting in a useful way with a voltmeter.

Cover your experiment dish with Saran wrap to keep the acid from evaporating from the vinegar. Common alkalis include bleach (don't mix with other stuff except water), laundry detergent, and antacids like Milk of Magnesia or Mylanta. You probably could mash up a Tums or Rolaids if you don't have a liquid antacid.

Regards,

A. Hi, Kenny. Just use the word corrosion instead of rust, and you're back on track. Yes, the nails will lose weight because you'll rub off any rust before weighing them and will be weighing only what's left of the metal.

Regards,

A. Hello, Lydia. If he's allowed to pick the liquids he wants to use, it makes no difference whether he picks distilled vs. apple vinegar, or real lemons vs. bottled lemon juice. If you're asking whether one of these is more corrosive than the other, though, isn't that the kind of thing these experiments are supposed to determine?

Glass is best, but plastics that are used for cups and bowls and food containers are unlikely to be affected by these liquids. A postal scale will not have anywhere near the precision necessary to gauge corrosion; but an electronic pocket scale might. Good luck.

Regards,

A. Hi, Letty.

What do you mean by 'attract the ions to the water molecule'?

If your experiment assumes Fe + O2 --> FeO2, would you expect the Fe to weigh the same as the FeO2? I certainly wouldn't.

I would put the steel wool [on eBay or Amazon] in the beaker, warm it to drive out moisture and weigh it. At the end of the experiment I would let all the water dry out, warm it, and weigh the remains in the beaker. The only thing is, the salt in the saltwater will not evaporate, so you must separately weigh the salt in the water before you begin.

Regards,

A. Hi, Ben. I suspect that you don't have a clear picture in your mind of exactly what you mean by rust. Assuming the school doesn't have an analytical balance, appearance is all you have to go by, and it will be a bit subjective.

I would leave the nails in the liquids until one of them shows a little rust, then pull it out and write down how many days it had been. Pull out the next one when it shows a little rust, and write down how many days. Continue until all (or all but one) have rusted. Then graph the name of the liquid vs. the number of days until first rust.

Regards,

A. Hi, Jennifer

Start with a "lab book". This is a composition book, rather than loose pages. The first thing you do is number the pages because this will remind you that you never rip a page out and you never erase. If at any point you write something that doesn't belong, strike it through but leave it legible. Now you write the date and time in it and you start writing . . .

You have three objects to test and three solutions to test. Three times three is nine, so you'll need 9 testing cups. You write that plan down and date it.

Have your parents help you find or buy 9 testing cups; maybe the disposable thin plastic bathroom cups would be good. Partially fill three cups each with the three liquids, and put a penny in one cup of each different liquid, and the same with the paper clip and needle.

Now every day for a week or two you simply look at the nine cups, see what you see, and write down the date and time and what you see in whatever words work for you.

As you start seeing things happen, some ideas and theories will start bubbling up; let them take you where they take you and start doing some research to try to puzzle out what you are seeing. Good luck.

Regards,

A. Yes, Kris.

You weigh the rusty nail, then treat it, then remove the pili pulp oil with an appropriate solvent, and weigh it again to see how much (if any) rust was removed. But I'm not sure how you would decide that removing the rust was a good and beneficial thing by weighing it :-)

It would seem to me that the rust is either a functional problem or an appearance problem, and the question I would have is whether the pili pulp oil improved the function or appearance.

Regards,

A. Black coffee has a pH of 5

A. Hi, Rinah. Thanks for the kind words.

Yes, how fast the iron corrodes and how much it rusts will depend upon the liquid that you expose it to. Your science teacher should have pH paper available for you. You dip it into the liquid and it turns different color depending on the pH.

It's cheap, fast, easy, safe ... and makes much more sense than trying to research the answers on the internet and trusting dubious sources :-)

Regards,

A. Hi, Rinah.

Has the teacher given you pH paper and shown you how to use it? What pHs have you tried? Are your questions 100 percent clear in your mind?

What liquids have you tried, and what were the results. I think we can help you reconcile your results with theory if you tell us your results; but to simply tell you the answers would be to defeat the purpose of the assignment.

Regards,

A. Hi. Sprite Zero is a secret formula. Without knowing what is in the secret formula, nobody can tell you for sure. But do you really mean "black" as opposed to rusty? Are the nails steel? Are they rusting in the other liquids as they should?

Regards,

A. Hi Taylor. Please very slowly read the first question and answer on this page and do your best to try to understand it. Acids like lemon juice will attack and dissolve the steel wool more and faster than less aggressive liquids, but they attack and dissolve rust even faster than metal.

Your temperature measurements indicated that the lemon juice was attacking the steel wool the fastest, and it probably was. But the acid is keeping the rust dissolved. If the rest of your experiment is over, you could try evaporating the liquids in oven set at about 225 °F. As you do, the rust won't be able to remain dissolved, so you should see a rapid buildup of it although the solids from the pineapple juice might disguise it somewhat.

Regards,

A. Hi Sara. Simply guessing wouldn't make for a very scientific science project, so see if you can go beyond that.

Iron and steel contain carbon that will not dissolve in acid, so if you've dissolved some steel, it might possibly be carbon left behind. See if it wipes off on a white cloth; if it leaves a black smut somewhat similar to carbon black, and if you can prove that the lemon juice is an acid, and if you can find a reference that says that acid can produce smut on steel, you will have moved from wild guess to reasonable probability (but not proof) that it is carbon. Good luck.

Regards,

Hi Mandy. Curiosity is a strong driver of scientific progress, but let's remember that this lesson is not for me or you -- it's for the kids. So my question back to you is whether this is the first and most important thing that the kids (rather than you or I) noticed and were curious about?

This is pretty advanced for me, let alone your kids, but I believe the black gunk is "black rust". I understand that it's what forms when iron/steel rusts but there is limited oxygen available, so instead of becoming red rust Fe₂O₃ (which requires 3 atoms of oxygen for each 2 atoms of iron), you get black rust Fe₃O₄ (which requires only 4 atoms of oxygen for each 3 atoms of iron).

Vinegar fumes are coming off of the liquid, and corroding the iron above the solution level, and because this action is inside a test tube rather than out in the open, not enough oxygen can get to the nail to form that much red rust, so you get black rust.

Regards,

A. Hi Ethan. This is a long page, and probably hard for fifth grade, but your exact questions are already answered on this page, some of them 3 or 4 times already. So the page should be a good exercise in reading for science, with slow and thoughtful contemplation :-)

Regards,

A. Hi Lucas. People smarter than you or I tell us that the more we learn, the more we realize how little we know. This can be a terrible frustration in science class, or it can be an inspiration because you'll forever have the fun of learning new stuff no matter how long you've been at it :-)

You've probably figured out that I'm about to deliver some bad news about what you've learned. Yep, just when you think you've learned that "pH = how acid or alkaline something is", I'm going to pull the rug out from under you and say "well, not really". There is a concept called alkalinity which might be accounting for you seeing more heat with vinegar even though you believe the pH of lemon juice is lower. There is probably "more acid" in the vinegar than in the lemon juice even though it's not reflected in the pH measurement. This video is a start towards understanding it, and you can go on from there into further researching "alkalinity" if you are interested.

Regards,

A. Lucas,
"Most acidic" can mean a lot of things. Keep in mind that you are dealing with two different acids here. (Bonus points if you know what they are called.)

Acids are molecule that let go of H+ ions when they are in water. pH is a number that tells us how many H+ ions are floating around in that water. However, there are a lot of other factors here. Some acids let go of all the H+ they have. Chemists call these strong acids. Other acids let go of some H+ but keep some of it too. We call these weak acids. (Both of yours are weak acids.) There are a lot of different weak acids and they don't all hang onto their H+ in the same amount. If you have two beakers of different weak acids with the same pH value, it means the H+ they let go of is the same, but the amount of acid needed to get that result is different. Chemists have to be very clear when they say a number about an acid solution as to what that number represents.

Then you throw in the wrinkle of reacting with a metal, and again, it depends on what type of acid you have. Solutions of different acids with the same overall amount of acid, or the same pH, can have drastically different effects on a piece of metal.

Keep in mind that at your level of schooling, you are not expected to know everything about chemistry. The point of this is to teach scientific method. You put together an experiment, you probably said what you expect to happen, and then you did it. Now you get to say if the real data matched your expectation or not. Scientists learn a lot when the real data is something other than what they expected. Typically your report would end by suggesting another experiment to help learn more about why your expectation was wrong. For instance, you might remove the variable of different acids by only using two types of vinegarwith different acid strengths. You don't have to actually DO that experiment, just say that's what you WOULD do as the logical next step.