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The effect of citric acid on steel


Q. I was just wondering if ordinary (household) citric acid has a corrosive effect on steel, aluminium, iron and copper. This is for a school assignment.


Brendan Mdeleted
- Sydney, N.S.W, Australia


A. I recommend trying the experiment yourself. Go get some lemon juice and put it on the various metals and record the results. Your testing may take anywhere from a few minutes to a few days, and you will have the satisfaction of discovering the answer on your own.

Good luck.

Dan Brewer
chemical process supplier - Gurnee, Illinois


A. Brendan,

Dan Brewer sure beat me to the punch! Yes, try things out yourself ... but to get some faster results, what about heating up the citric juice, this increases the molecular activity (so someone once said to me) and being lazy and as a teenager (well, I was one once, long, long ago) I'd want a fast answer.

Others follies teach us not
Nor much their wisdom preaches
But most of sterling worth is what
Our own experience teaches. (by ANON, not by me!)

You might remember those lines. Very true, too. And by doing something like this YOURSELF, you'll always, always remember it which you won't if you are given a simple answer.


freeman newton portrait Freeman Newton
- White Rock, British Columbia, Canada
freeman newton died

Science Fair Projects for Elementary Schools

Science Fair Projects

Does lemon juice rust steel?


Q. I am doing a science fair project on the corrosion effect of different substances on steel. One of the substances I chose was lemon juice (citric acid). I have to say what is in the citric acid that's causing the steel to rust. I have no idea. Can you tell me?

Thanks heaps,

Emma R.deleted
Student - Wellington, New Zealand


A. Hello,

Citric acid reacts very quickly with iron, but does not in itself rust the iron. The water in the lemon juice will help to rust the iron, however, in the presence of air. A steel nail dropped into a citric acid solution will dissolve in a matter of hours. The same thing happens if you drop it in a bottle of "Coke", which has citric acid, phosphoric acid, carbonic acid and other things in it for flavor.

If you need help with your project, let us know. We work with citric acid products every day and have a lot of data.

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois

Thanks Lee. "Dissolve" is probably too strong a word though; let's say "begin to dissolve". I've found that a bowl of Coke will not completely dissolve even the innards of a copper plated zinc penny in a month, let alone a nail :-)


pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

Why does juice clean copper?


Q. I work with pure lime, orange, lemon and grapefruit juice (which I understand contains citric acid) for a science project in school. I tested the pH value of the respective fruit juices and placed separate pieces of copper strips in each fruit juice. After a while I saw that the copper strips turned shinier than before. Is there an explanation for this?

Nas Wdeleted
- Singapore


A. Pure citric acid does not corrode iron. In fact, it is a very effective rust remover and used widely for that purpose! As you have noticed, it will remove corrosion and leave clean, bare metal. Corrosion will set in due to the contact with air and humidity afterwards. I have myself cleaned rusted, chalked up cast iron cylinder heads by dumping them in citric acid solution and they came out like new.

Holger Kneisner
- Braunschweig, Germany


Q. To whom it may concern,

I am doing an experiment regards on citric acid and rust in school. As I was doing my experiment, I was curious of what is the chemical equation of the citric acid and rust or either the product of the citric acid and rust when its being reacted together. It would be appreciated if you know any of references or websites that would help me to get more information about my experiment.

Thank You.

Ramona Pdeleted
student - Pago Pago, AS, American Samoa

A. Hi Ramona. The thing is, acids will attack ("begin to dissolve") metals, with variable success depending on the particular acid and the particular metal ... but they will dissolve the "tarnish" or "rust" (metal oxides) easier and faster than they dissolve raw metal. So the first thing you usually will see is tarnish removal or rust removal. That is because the metal oxide that was on the surface is now dissolved in the acid. But if you let the acid evaporate so the metal that was dissolved in it cannot stay dissolved, you'll see a rusty mess :-)


pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

Does citric acid dissolve copper?


Q. Hi I'm wondering for a school project will citric acid rust away a strip of copper and if so how long would it take?

Jessica J.deleted
student - Port Stephens NSW AUST

March 2014

A. Hi Jessica. In science class we have to use words more carefully than around the house. Copper doesn't "rust" because "rust" is defined as the corrosion product of iron; and copper is not iron and doesn't contain iron -- but copper can dissolve or corrode or tarnish.

As Lee says above, the citric acid itself doesn't cause rust, it's a bit complicated. The acid can dissolve copper, but it's oxygen in the water that combines with the dissolved copper to form copper oxide tarnishes. A large bowl of citric acid might completely dissolve a very thin and very small piece of copper foil in a reasonable number of days.


pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey


Q. In a book called "400 Hints for Homes" the following sequence sequences is given for the removal of a rust stain: "Moisten with lemon juice, add salt and dry in the sun. Rinse off and repeat if necessary". Can I know the chemistry and physics of this operation

student - Batu Caves, Selangor, Malaysia


A. Hi,

I believe all depends on concentrations. The nail in citric acid may be true at 100% concentration, but we actually demonstrate the OPPOSITE. At around 0.2% (2000 ppm) of citric acid in water, a nail actually coat itself gray and ABSOLUTELY NO rust appears. Pure tap water results in comparison in ugly corrosion.

I did no detail study on concentrations and their impact.

Does anyone know at what concentrations citric acid acts corrosive, and at what concentrations it acts inhibitive on corrosion? Citric acid is actually termed to be an ANTI-OXIDANT. Go figure.

Looking for any clarifications.


Hans J.Krause
- Montreal, Quebec, Canada

February 25, 2012

Q. I'm working on a project to find out why lemon juice can remove rust on a paper clip. Can anyone give me a help? I'll really appreciate that. Thanks.

Ruth Ydeleted
- Hong Kong, China

February 27, 2012

A. Hi Ruth.

Acids like citric acid dissolve metals but they dissolve rust (metal oxide) faster. Your chemistry book may tell you that an acid plus metal will yield hydrogen plus a salt of that metal.


pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

February 28, 2012

Q. Chinese old folks believe cooking lime juice or vinegar in a steel pot is bad for health.
So is this a myth or it is true? As there is a chemical action between citric acid and steel when heat is added, we are consuming the rust and whatever deposit in the food that are harmful of our body.

Q Susandeleted
- Singapore

March 2014

A. Hi Susan. Sounds like a great topic for you to do a research paper. Surely the acid will dissolve some iron, but iron is an essential nutrient, not a poison. So, does it dissolve so much that it could make for a harmful overdose, or such a minimal amount that it has no effect on health? You'd have to experiment to figure out how much it dissolves, and study up on what a normal daily intake of iron should be. Good luck.


pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

January 5, 2013

Q. What happens when you put copper, steel, aluminum, and brass in pure lemon juice? And why does it happen.

Jonah deleted
- New York, New York, USA

January 6, 2013

A. Hi Jonah. Yes, that sounds like a good topic for a project. Let us know what happens when you do it, and we'll try to help you explain your results.


pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

November 3, 2013

Q. What liquid will make a steel nail rust faster: orange juice, vinegar, salt water, or tap water? Please help. : )

Anna deleted
- Weehawken, New Jersey, U.S.A.

November 4, 2013

A. Hi Anna. Yes, that should be a good project too. Get four non-metal bowls, put those four liquids in the bowls, put a nail in each (fully submerged) and start recording what you did and what you saw in your lab book (a notebook where you've pre-numbered the pages, so you are not tempted to rip a page out). If you think you recorded something incorrectly, strike it through once but leave it legible.

Then come back in a week with your observations and we can comment on them. But please don't make the mistake of trying to figure out which of the four liquids should cause the most rust until you've actually done the experiment. Because if you do, you will be tempted to discount contrary observations and give too much weight to observations which agree with your expectations. You would learn a lesson in "junk science" instead of real science; junk science should be avoided until you are a hungry climatologist looking for a grant :-)
Best of luck.


pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey
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