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2003
Q. I am working on a science fair project to see how pennies corrode. I chose six liquids and air and put clean, bright pennies in them for seven days to see how they would corrode. The two most interesting results happened in bleach and vinegar [affil link]. The bleach corroded over the first night. The penny in vinegar [affil link] didn't really start to corrode until the vinegar [affil link] evaporated and then the penny turned blue. I am not sure why these pennies corroded the way they did could you tell me more?
Stephanie F. [last name deleted for privacy by Editor]
elementary - Los Alamos, New Mexico, USA
A. Hi, Stephanie. First off, I hope your teacher and your parents warned you at least 5 times not to mix anything in with the bleach. Adding vinegar [affil link] to it can release poisonous chlorine gas.
Bleach is highly alkaline and the zinc core of pennies dissolves readily in alkaline materials. Also, bleach is very high in chlorides, which are devastating corrosion-wise for most metals. vinegar [affil link] is an acid which cannot dissolve copper but can dissolve the zinc core of pennies. But, moreover, vinegar [affil link] can dissolve the brown oxide that is present on most older pennies, leaving a bright surface on the penny. If the vinegar [affil link] evaporates, the copper that it dissolved from the tarnish will dry out as a blue green copper salt. Good luck wrapping up the project.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April 30, 2012
This is great info! THANKS SO MUCH! My 5th grader did this same experiment and the bleach corroded the penny greatly! I love the internet. I typed in this question and someone was nice enough to not only already have asked this question, but another had it answered perfectly! A million thanks from a 5th grader's mom!
Stephanie M [last name deleted for privacy by Editor]
- Magalia, California USA
Ed. note: Students please search the site for similar letters or read our F.A.Q. on the subject. Good luck.
November 12, 2012
Q. Hello my name is Vita and I have a question:
Why does copper corrode in anything at all, and alsowhat corrodes it best Coca-Cola, vinegar [affil link], or muriatic acid
Thanks a million :)
Vita [last name deleted for privacy by Editor]
science fair - San Diego, California, USA
November 13, 2012
A. Hi Vita.
Who says it does corrode in any of those things? I'm quite sure it doesn't. Do the experiment first with Coca-cola and vinegar [affil link] and other household stuff. I'm not sure of your age and whether you can safely experiment with muriatic acid, but I would strongly discourage it except under the supervision of your science teacher.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
November 22, 2012
Q. Ok so in my previous Q's you stated that some of my substances will not corrode possibly. So why do copper pennies corrode at all? Thanks Mucho :)
Vita [last name deleted for privacy by Editor]
Sciencefair CONFUSION - Irvine California, US of A
November , 2012
A. Hi Vita. You have probably seen that brand new pennies are bright reddish copper color, but they eventually become dark brown. That brown coloration is tarnish or corrosion. So, yes, copper pennies corrode. In fact, all metals except gold, platinum, and similar precious metals corrode.
The basic driving force behind such corrosion is that the reaction product, corroded copper, is at a lower energy state than the uncorroded copper. If you touch a lit match to a piece of newspaper, you know what happens: the paper catches on fire, takes oxygen from the air, and gets hot; smoke floats off, and ashes are left behind. But if you touch a lit match to the ashes, nothing happens. While the burning newspaper was hot, it gave off heat, so it ended up in a lower energy state. There is no way to get from ashes back to newspaper without adding that heat back in.
In a somewhat similar but much slower way, copper combines with oxygen from the air, very slowly releases a small amount of heat, and you end up with copper oxide on the surface of the penny. You can't convert that copper oxide back to uncorroded copper except by adding heat back in while excluding oxygen. If you look into how copper is made (or other non-precious metals like iron), ores are melted (heat is added back in) while oxygen is excluded.
So, yes, the oxygen in air will slowly corrode copper by combining with it and releasing heat.
Your situation is to determine by experiment whether you can speed up or worsen that corrosion with coca-cola or vinegar [affil link]. Don't ask why they speed it up until you know from experiment whether they do :-)
Please note that you must find pennies from 1982 or earlier because after that they are not solid copper, but copper coated zinc. Using a copper coated zinc penny changes everything because there may be pinholes or porosity in the copper plating, so your ingredients will then be working against zinc instead of copper. Good luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April 16, 2015
Do zinc pennies dissolve in vinegar [affil link]? And if they do, why?
Alex R [last name deleted for privacy by Editor]
- aurora,ON,Canada
April 2015
Hi Alex. Why do polar bears frolic in yellow & blue canoes on the Amazon ... if they do?
Don't even think about trying to get an answer to why zinc pennies dissolve in vinegar [affil link] until your experiment determines whether they do or not. It's silly. Plus, if we tell you that they do or don't, then you won't trust your own experimental data and will be tempted to fudge it -- that's called "junk science" and should only be practiced by starving climatologists. Please describe your experimental method. Thanks.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April 22, 2015
Q. Hello
My name is Brad and although I'm not a student experimenting in the corrosion of pennies, I have a question that I believe you will have the right answer to ... I included pics for you to view of samples of the big bucket of pennies that may or may not be salvageable. Some time ago a friend's child was going to help me clean them and left them in either bleach or something and therefore damaged them and they have been put aside until now. Could you please let me know if anything can be done at all?
bradley hawthorne
- Baton Rouge, Louisiana
April 2015
A. Hi Brad. We didn't get the pic ... you can email it to if you wish, but we don't have experience in that anyway. I suggest that you look at letter 25530 regarding how to attempt salvage or where to send the coins. People in the coin salvaging business will want to save as much of the coinage as possible because they get a cut of the salvageable coins. Good luck.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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