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Rate of penny corrosion



A discussion started in 2004 and continuing through 2017 . . .

(2004)

Q. Our lab is currently conducting experiments on the nature of acid corrosion on the 1989 U.S. penny. In one of our tests, we are submerging the penny in 300 ml of Coca-cola, in an Ehrlenmeyer flask, and measuring change over time. My question is, do you know of any empirically supported documentation showing the rates of corrosion and/or at what rate the penny will actually dissolve (if at all)?

Thank you,

Kevin J. [last name deleted for privacy by Editor]
microbiologist - Los Angeles, California


(2004)

A. Hi Dr. Kevin. I can't decide if you're posing your question in this style to trick people into doing your homework for you, or if you are enthusiastically playing the role described for your hypothetical science research project. But you sound pretty cool :-)

But why 1989 pennies rather than 1988 or 1990? What do you think them different?

Why Coca-cola, which is a hodgepodge of secret ingredients, and whose acidity is supported by volatile carbonic acid, rather than a repeatable and documentable reagent like .01 N HCl or something?

After you do your trial, let us know what corrosion rate you got; it would be fun to discuss. But the thing is, trying to look up the answer first when you're still in school seems like carefully training students in the art of "junk science": the kids look up what the answer is "supposed to be", and learn to fudge their experiments to interpret them that way -- chalking up their real observations to experimental error, or otherwise discrediting them, giving far too much weight to the scantest result that supports their preconceived notions, etc. I suggest you somewhat alter the scientific method by doing the experiment first and recording your results, and then do the research after you know what happens :-)

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


(2004)

A. Will you see some long term attack on the penny, Yes. Far too much depends on how clean the penny was when you started (oxides, grease, etc.), the temperature that it is kept at, the amount of agitation, can the Coke effectively get to both sides, how often are you cleaning the resulting smut off of the penny, the effect of the increasing sugar content as it slowly evaporates. Too many variables and no one cares enough to document (publish) the results if they had done any work. Coke certainly is not going to talk about it. If you want a real life shock, put a 1" cube of lean steak in the same 300 mL of Coke and put cover on the flask or beaker.

James Watts
- Navarre, Florida


(2005)

Q. Dude, I need to know about how long it takes for the penny to show a change.

Katherine R. [last name deleted for privacy by Editor]
- Austin, Texas


(2006)

A. How long does it take for the hour hand on a clock to move, Katherine. How big a change? How long have your coins been immersed without showing any change? Coins wouldn't be very useful if they quickly corroded away. Good luck.

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


(2006)

Q. My daughter is in 3rd. grade and would like to do her science project on the corrosion of a penny. She's 9 years old so this is new for us. I am trying to help her and we thought we would put the pennies in small cups with some general items she can work with such as water, Coke, lemon juice, bleach, and maybe hydrogen peroxide [linked by editor to product info at Amazon]. I will have her watch the changes and note what takes place first. Am I on the right track? Any other liquids you could suggest would help and do I need to cover the cups? And she only has three weeks -- is this long enough? Thanks so much for all the help you can provide.

Christina D. [last name deleted for privacy by Editor]
student - Swartz Creek, Michigan


(2006)

Q. Hi I'm in 8th grade I'm doing a science fair project on penny corrosion; my question is as follows:

My question is for my science fair. I'm doing a project on which a penny corrodes faster in: coke-cola, lemon juice, and orange juice. I was thinking of putting the pennies into 3 different cups each filled with 3 tablespoons and the 3 different liquids into each cup. I am going to try and time the amount of time it takes for each penny to corrode. I will check on it every 5 min stopping at 15 min. Is that too short of time? well please get back to me as soon as possible? Thank you.

Mercedes A. [last name deleted for privacy by Editor]
Student - Chicago, Illinois


(2006)

A. You're doing fine, Christina. Cover the cups if you expect the test to last longer than about 2 days.

I think every day for 3 days is much more reasonable than every 5 minutes for 15 minutes, Mercedes. I'd suggest using post-1982 pennies, and cutting them into pieces.

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


(2006)

Q. I am doing my brother's sixth grade science fair project. Yes, he is getting away with murder because I am in 10th grade. Anyway, sodium hydroxide is a great base to test penny corrosion. It is a base with a pH level of 13 and it really surprised me. Try it. Anyone got any tips?

Andrew d [last name deleted for privacy by Editor]
- Irvine, California


(2006)

A. Hi Andrew. Sodium hydroxide is very strong and dangerous; I don't think even a tenth-grader should use it, but if you do, be careful to wear goggles [linked by editor to product info at Amazon]. Sodium hydroxide probably has less effect on solid copper pennies (before 1982), but I'm sure that you are right that it is murder on zinc core pennies (after 1982). I suggest you chop them into pie slices before putting them into your liquids.

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


May 13, 2009

Q. Thank you Ted for adding some humor to this thread. :-)

I am an archaeological student and during our lunch break I found many interesting items on the beach (we're digging more inland). Of the many things I found there were about 5 handmade rusted spikes. My instructor said I could keep everything I had found there and that I should soak the items in vinegar or Coke. I threw a penny into my test bowl for fun to see it get its shine back. Just for reference sake, how long (approximately because I know there are MANY factors) would it take for the Coke to do serious damage. I'm aware that the artifacts and penny are different materials, but I was just wondering. I was also just very curious about how long it would take to corrode a penny and I also wanted to post on this thread...

Melinda Maclean
- Portland, Maine


May 14, 2009

A. Hi, Melinda. I think Coke will have little effect on solid copper pennies (before 1982). It would seriously corrode (make pits in) the zinc core of post-1982 pennies in a few days depending upon finding any holes in the copper plating.

Iron spikes, unfortunately, I'm not very familiar with firsthand. I'm sure it will dissolve a good portion of the rust on them though. I would not expect it to attack the base metal while there is still significant rust on it because rust dissolves into acid much faster and easier than metal does. Good luck.

Regards,

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


April 21, 2010

Q. I am in 5th grade. I'm using pickle juice, ketchup, coke, water, and salt water to corrode pennies how long will it take and will any of them corrode?

Jordan S
student - Perryville, Kentucky, USA


April 22, 2010

A. Hi, Jordan. Make sure your pennies are 1983 or later. Ask your parents for help cutting them with tin snips to expose the zinc core. Some of them will corrode. A week is enough time to see what you've got, but I doubt that any are in danger of disappearing in that length of time. Good luck.

Regards,

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



November 17, 2014 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I'm doing a project on Crystallization on pennies with bleach, vinegar, water and dish detergent and I can't seem to get anything on it for research. Any tips for an eighth grader?

Halona W [last name deleted for privacy by Editor]
Science fair - Canton Ohio USA


November 2014

A. Hi Halona. My advice on this subject is always the same. Please share my answer with your teacher and I think s/he will agree --

1. If you don't know the answer to a question, that's what research is for and about -- get busy.

2. But if you don't understand the question, tell your teacher and get clarification; because nobody else can clarify the question for you ... all they can do is take wild guesses that will certainly confuse you and possibly mislead you.

My *guess* is that you misunderstood the teacher's question and are trying to bull on through anyway. It probably won't turn out well unless you go back to him/her and ask what s/he means by "crystallization on pennies" :-)

Regards,

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



February 23, 2017

Q. Why does lemon juice disintegrate pennies; answer asap, thanks.

violet chen
- nyc, New York


February 23, 2017

A. Hi Violet. Does it? Please don't ask why it happens until you've put pennies in lemon juice and found for yourself whether it does in fact happen or not. As the renowned physicist and wonderful teacher Richard Feynman said: "It doesn't matter how beautiful your theory is, or how smart you are, if it disagrees with experiment, it's wrong." =>

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"

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