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    Chemistry Of The Penny: Influenced By Economics And Medicine
    By Enrico Uva | February 12th 2012 07:51 AM | 8 comments | Print | E-mail | Track Comments
    About Enrico

    I majored in chemistry, worked briefly in the food industry and at Fisheries and Oceans. I then obtained a degree in education. Since then I have...

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    Over the years, economic and even medical considerations have influenced the composition of pennies. At one point they were almost pure copper, but presently copper is only a veneer used to maintain an illusory link to the past.

    Why copper in the first place? Unlike iron, copper does not become more prone to oxidation in water. It even resists the action of certain acids such as vinegar and dilute hydrochloric acid. Copper does react with oxygen, but only gradually, leading to the darker and duller brown color of older pennies. But if kept in a pocket or piggy bank, pennies do not bind to hydroxide(OH-), sulfate(SO42-), or chloride(Cl-) to make the compounds of the patina found on statues and roofs. 

    In 1974 the United States toyed with the idea of an aluminum penny. Aluminum, like chromium and titanium, oxidizes quickly, but the shiny oxide coating clings tightly to the rest of the metallic structure, thus protecting it from further damage. Aluminum is also less expensive than copper. But although over 1.5 million pennies were minted, they were never released into circulation. Not only did copper and vending machine industries lobby against it, but pediatricians argued that if lodged in air passages or in the gastrointestinal tract,
    aluminum pennies would be difficult to pick up.

    In recent decades, the price of copper has risen substantially. In February 2012, copper was valued at about $3.80 US per pound, zinc at $0.96 and steel at $0.39. There are 16 ounces in a pound and 28.3 grams per ounce, so that minting a 3.24 gram 1990 Canadian penny would now cost $ 0.027 per penny in materials alone. By dramatically reducing the copper content, the mint has reduced the raw material cost of a 2012 Canadian penny to less than a cent.

    The total cost of minting each penny, however, still exceeds a cent, regardless of whether the core is mostly steel, as it is in Canada and Europe, or zinc in the United States. (This is why only American pennies have remained nonmagnetic.) The high cost of minting pennies is just one of the arguments in favor of eliminating the penny. Due to inflation,
    a nickel today is worth what a penny was in 1970.
     COUNTRY YEARS COMPOSITIONMASS (grams)
     Canada 2000-present 94% steel
    1.5% nickel
    4.5% copper-plated zinc
     2.35
      1997-1999 98.4% zinc
    1.6% copper plating
     2.25
      1942-1996 98% copper
    2% tin-zinc mixture
     3.24
     United States
     1982-present 97.5 % zinc
    2.5% copper
    (but less copper in plating)
     3.1
      1864-1982 95% copper
    5% zinc or zinc-tin
     3.1
     Eurozone copper plated steel
     2.30
        

    Sources for table: various Wikipedia
    articles

    On the subject of elimination, aside from using a magnet, another way to reveal that copper only coats a Canadian penny is to expose it to concentrated nitric acid (
    HNO3)for a couple of minutes. Nitric acid contains both acid(H+) and an oxidizing agent(NO3-), a combination that quickly converts copper metal into ions, leading to a deep blue solution. But the small percent of nickel in the steel gives the core longer protection against the corrosive action of HNO3. So what comes out is a silvery penny(just in color, of course!). As an alternative, cutting a penny will also reveal that the inside is not brown. Another experiment suggested by an American reader: cut a Lincoln penny with pruning scissors, then expose it to HCl. After a few hours, the zinc will all be gone, and the only thing  left will be a thin copper outer shell. Neither method is recommended since I'm not sure about the legality of destroying coins. But I wonder. If writers have poetic license to adulterate spelling, split infinitives and force rhymes, do chemists have a license to damage pennies in order to reveal their true composition?

    Postscript
    **First I followed instructions and then I didn't to create brass-covered pennies and one gone completely awry!

    Comments

    The copper coins are generally worth 2-3 times their face value for the base metal. 

    Even the 5c "nickel" is worth a little bit more. Banks should give you bags of them for change, no questions asked so there's foolproof arbitrage there - if you can find a company willing to accept nickels as scrap at spot prices.
     
    http://www.coinflation.com/
     
    UvaE
    Thanks for the link, Derek. They have $0.025 (rounded for significant figures)as a value for the almost pure American penny. I had calculated $0.027 for a Canadian one. That's pretty close. As my table reveals, the 98% Canadian penny was a little more massive. The two currencies are currently close to par.

    Also, I apologize for the editing errors in the original article. It's been patched up.
    I have cut post 1982 pennies in my chem class, and placed them in HCl. Zinc gone, copper left behind. Weighing before and after gives them an idea of just how little copper is used. Can use for activity series, moles, etc.
    They are also shocked that you could cut metal that thick with a scissor.

    Thanks for the posts BTW...as a fellow son of Italian immigrants, I also appreciated the wine making one.

    UvaE
    Thanks for the posts BTW...as a fellow son of Italian immigrants, I also appreciated the wine making one.

    Let's each a raise a glass of wine, and as they say,
    "Per cento anni!"
     

    And to chem ed of course.
    UvaE
    Coincidentally, less than two months after writing this article, the Canadian government announced that it will stop producing pennies.
    The Royal Canadian Mint in Winnipeg will stop making pennies for Canada next fall, Finance Minister Jim Flaherty said Thursday. The measure was one of the highlights of the 2012 federal budget, even garnering its own glossy brochure in the budget documents.
    http://www.winnipegfreepress.com/local/penny-scrapped-martin-applauds-145086075.html
    The equation is simple, produce penny coins is too expensive for the benefit. Nice tip:"On the subject of elimination, aside from using a magnet, another way to reveal that copper only coats a Canadian penny is to expose it to concentrated nitric acid (HNO3) for a couple of minutes. "

    http://www.nitricacid.info/nitric-acid/uses/

    I still regard the penny as valuable, or more valuable, than the cost to produce it compare to it's "face-value". I look around me and find a penny that is from 1972 and realize that this is indeed one heck of a durable item. I wonder just how many times it has been "used"? And yet, it's still worth a penny.! If it were like most other items nowadays, where things are used once or maybe twice, then i would agree it would seem invaluable and worth less than a penny. HipHipHooray for the penny!

    UvaE
     I look around me and find a penny that is from 1972 and realize that this is indeed one heck of a durable item.  


    Nice, contrarian view!