So my son and I came up with a good science experiment for his fourth grade science fair project. He is going to see which type of water causes metal to rust more quickly? Ocean, pond, tap, mineral or soda water. I need help though with a few things.
What metal will give the most dramatic results over a 45 day period? I’m thinking drywall screws maybe?
Also what’s the best environment for this type of experiment? I was thinking he could spray the samples twice a day and let them sit on the porch? Does this make more sense than leaving the metal in the cups of the water?
Would a better experiment be to get 5 types of metal and see which one rusts the most?
I’m looking to set him up for some dramatic rusting so it’s fun and he can take pictures and track progress over a 45 day period.
I’m a EE so I don’t really know much about this particular subject. Any help here?
I remember a demonstration in 7th grade using steel wool (without soap, obviously). Lots of surface area. The lesson was about catalysts. I don’t remember what my teacher used as the catalyst, but the steel wool rusted nigh instantly.
To be safe, I would run it in parallel in different environments, and use the one that shows the more interesting results. It would suck to be spraying for several weeks and end up with very little rusting.
I would not leave them submerged; they might not noticeably rust at all. The spraying should work, but it is possible then that they all might rust so much as to be indistinguishable, especially if you go on with it for too long. The idea of varying the metal samples rather than the liquid might work better, if you can find enough suitable samples of different types of ferrous metals.
My answers are based on what I learned working in an archaeological conservation lab, dealing with highly corroded items which had been, variously, in dry, moist, and submerged environments. But IANAChemist.
Rust is an oxidation process so I think for optimal results you do need corrosive material PLUS air. If the item is fully submerged it will still oxidize but I don’t think it will do so as quickly as if it were regularly exposed to air. I think the spray bottle + porch is a good choice.
Drywall screws have a lot of surface area, which is good, but they also have a phosphate coating that inhibits corrosion so I think they would a particularly poor choice. I believe the “worst” screw for outdoor applications (ie, the best screw for your application) is an uncoated steel screw which is NOT a stainless steel screw. Edited: Strike that, steel wool is a brilliant choice. It’s got tons of surface area and is easy to obtain in large pieces that will show results clearly (unlike a screw).
Its certainly a different project. The thing that makes an experiment an experiment, is that you don’t know the results when you start. When you see the results, you learn something about the process and can determine whether your initial hypothesis was correct. This is generally “the point” of 4th grade science fairs – to test a hypothesis. Since only ferrous metals can rust at all, I think the multiple metals project is a lot weaker because it will provide results that are already extremely common knowledge. If you know for a certainty what you’ll get when you start, you’re doing a demonstration, not an experiment.
If you use steel wool, you’ll get results overnight if not sooner. If you can acquire a sensitive scale, you could quantify the rusting. Iron oxide will weigh more than the original iron’s mass of approximately 56 g/mol. The rust will be a combination of iron (2) oxide and iron (3) oxide which have molecular masses of around 88 g/mol and 159.6 g/mol respectively. What this means in 4th grade speak is that rust weighs more than the iron it formed from, so the heaviest of the rusted samples is the rustiest.
Want really fast rust? Try seawater (3.5% salt by weight).
I was going to suggest taking a picture every day of all the samples for this very reason. My guess is that after 45 days they’ll all be totally covered in rust and look exactly the same.
How handy are you? How about some plywood with some samples on them?
I’m thinking, a row (across) of drywall screws. Another row of steelwool. Maybe some stainless steel (maybe with a nice gouge or scratch in it for fun). Some other metals as well. Then you could spray the different metals from top to bottom with the different waters and leave it propped up against the side of your house to drip dry. Also, you’ll have to decide if you’re going to give it shelter in between sprays or leave it out in the rain/weather like most rusting materials are.
If you did it this way, you might also want to route a slot between each row so the drops can fall to the back of the board and the rusty water doesn’t contaminate the sample below it.
At some point during his project you might help him ‘notice’ that brake disks rust in a matter of hours. It’s easily noticeable on the street or in a parking lot.
You can test it by doing some driving (might be helpful if it’s humid/damp out) point out how the disks are nice and clean and look for the rust spots in the morning. I’m not sure what it’ll prove, but you might be able to work it in somewhere. Maybe try to figure out what kind of metal the disk is made of.
BTW, don’t touch it after you drive it. It’s hot.
This. Here is the most important science lesson a practicing scientist needs. (Although may be a bit too abstract for the 4th grade level.) Do the experiments, then cherry-pick the results!
Another vote for steel wool, no soap, taking pics along the way. Glue several samples on a plastic background, label, and spray with the water samples. Then display with the pics showing the progress of the rust.
Metallurgist here, so this may be kind of cheating.
Get different metals with different finishes.
A common (10 penny or larger) nail generally has no finish at all.
A drywall screw (and some kinds of nails) has a black oxide finish.
A galvanized nail or screw has a zinc (obviously) finish.
A stainless steel screw.
A piece of copper wire (10 gauge electrical wire, which is about as pure copper as you will see)
A piece of aluminum wire (if you can find it, about the same gauge as the copper).
That should give you about a good assortment of metals as you can easily get.
Sea water (assuming you live where you can get it easily). You should be able to get a analysis from somewhere.
Mineral water (tough to get an analysis for, but if you do some research, you can probably find a brand that has an analysis).
Tap Water (get a water report from your water supplier).
Distilled Water.
If you know somebody who works in an industrial environment, some treated cooling water. They add chemicals to that water to prevent corrosion. The MSDS for the treatment should give information on what is in it.
A lot of jars with tops.
One metal and one type of water in each jar. Take a picture of each one every day.
This should give some very interesting results. Compare what is in the water with the corrosion results.
excavating (for a mind)
Even better…find some already rusted metals and and work backwards until you get to your hypotheses.
I can think of a few physics papers where the first thing the group started with was someone saying ‘What answer/percentage/deviation do we want to come up with?’ and then working all the equations backwards until the results we had the results of the ‘experiment’.
Might be interesting to see what you can add to the water to retard rusting too.
When my parents did Amway (that is, before it destroyed their lives), one of the demonstration aids for their laundry detergent was steel wool in a screw top jar filled with water and a little of the washing powder, alongside similar examples of store-bought brands - for some reason, the Amway washing powder completely inhibited rusting - the others all turned into really interesting chemical soups.
But I guess whatever it is that stopped the rusting is probably something quite simple,
Steel wool will be an unrecognizable lump of crap within a couple days, and a little bit of it will wash away every time he wets it. It will have to be in a container and there may not be much left after 45 days.
Steel wool would be good if his project is to see how everyday objects rust, but if his project is to compare different materials, they should all be a similar shape and size. Steel wool will rust into a pile of goo in 45 days while a piece of steel will just get a coat of rust.
I would use pieces of black iron pipe (Lowes or any good plumbing supply house). Clean off any coating. That way you avoid the effect of different steel alloys.
I’d really prefer cast iron, but I can’t think of a source for small bits.
A plumbing store would have it. A hardware store probably would as well. A couple of small diameter elbows would get the job done. I was going to suggest taking a bigger piece and smacking it with a sledge hammer a few times to shatter it, but I’d imagine that would leave sharp edges.
It’s probably going to be painted though, so the finish would need to be sanded off in one spot to let it rust. OTOH, I’d imagine any male connections would have visible and unpainted threads.
Peopel have suggested a range of material, but you said ‘different types of water’. If that`s the case, you need a fixed identical medium for the metal. I like the steel wool idea, it’s the material that IMHO rusts pretty good. I like the idea of weighing it. If you went with types of metal, you would have to know what metal each sample is.
My suggestion would be a set of disposable tupperware type containers. put a measured amount of steel wool and maybe a half or quarter inch of water. Seal after wetting. Maybe shake well every 6 or 12 hours to re-wet. Sealed container means the water does not evaporate, does not concentrate whatever impurities might aid rusting. Secondary observation might be whether immersed part rusts faster or slower, whether heat or sunlight makes a difference. Open every day to ‘refresh’ the air in case it is oxygen starved? Try some other choices, like add 2 drops of vinegar (nice acid) to one containers water. For another, add detergent or soap -something basic. Bleach? Sea water or salt water? 7-Up? Coke?
The digital camera to record progress would be good. Set up a nice white backdrop set and good lighting, take pics every day? Record it all in a journal.
In actual science fairs, I judged in a few, they are (I hope) looking for the standard hypothesis - experiment- results - conclusion, and an organized and critical thinking to ensure the experiment is clean and the results unlikely to be misdirected.
The experiment as written is to see how 5 different types of water cause a metal to rust. He can only have one variable so it has to be different metals or different waters.
Can he ‘cheat’ and use different metals anyways? You’d/I’d hate to get to the end and find out the metal dissolved completely in two days or hardly had any reaction to any of the waters after only 45 days because you chose the wrong metal. At least if you picked a few you could then take the one that should the biggest range of differences across the various types of water and present that.
He’s in forth grade, is he really expected to know that a handful of stainless steel screws that he found in the basement aren’t going to do anything in 45 days (for example).
If he really has to pick just one thing. I suppose I’d go with something like a chunk of electrical conduit or paper clips or rebar. Things that, if you see them outside somewhere, are typically rusty.