Kids, have you ever seen a copper-colored nail? In this month’s activity you will make one of your own. First you will need the solution left over from last month’s experiment (Metal Mania – Part I). If you didn’t save the solution or if it has degraded, have fun repeating that experiment now!
Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
While you are waiting for the pennies to do their thing on the paper towels, use the salt and vinegar solution to make some “Copper Plated Nails”. Place one clean ungalvanized iron screw or nail so that it is half in and half out of the solution you used to clean the pennies. If you have a second nail or screw, let it sit out on a counter for comparison (your “control experiment”). We also placed a masonry nail entirely in the solution. Do you see bubbles rising from the nail or the threads of the screw? Allow 10 minutes to pass and then take another look. Does the metal have two different colors? If not, return the nail or screw to its position and check it again after an hour.
Eventually, the copper in the solution from the pennies will coat the nail or screw. How does that happen? Copper exists in the salt/vinegar solution as positively charged copper ions. The reaction between iron metal and copper(II) ions is called an oxidation-reduction reaction. Iron is more active than copper in this reaction, which means it loses electrons more easily than Cu. In other words, copper(II) will take iron’s electrons, causing it to plate out as metal (it is “reduced”) on the iron nail (which gets “oxidized”). At the same time, the reactions involving the hydrogen ions from the acid and the metal produce some hydrogen gas, which bubbles up from the site of the reaction - the surface of the nail or screw. When you take the nail out of the solution, the copper will be somewhat sticky; you can set it on a paper towel to dry. Your nail might not be entirely coated, but it will have enough copper on it to see.
You might try this experiment again using only pennies made before 1982. These contain 95% copper as opposed to only 2.5% Cu in pennies since then. Did the nail get a copper coating more quickly or in the same amount of time? Was it a more complete coating? What happens if you use a stainless steel nail? Come to think of it, what exactly is “stainless” steel? First, steel is iron with some carbon added to make it harder and stronger. Adding a minimum of 12% chromium to the steel makes it resist rust, or stain 'less' than other types of steel. The chromium combines with oxygen in the atmosphere to form a thin, invisible layer of chrome-containing oxide, making a passive film. So, what does that tell you to expect from a copper plating experiment using a stainless steel nail?
NOTE: The accompanying photo on the website version of this article shows two types of iron nails and their controls; one was placed entirely in the solution and the other was in 1/3 of the way.
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Kathleen Carrado Gregar, PhD, Argonne National Labs
[email protected]
April 2006
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Reference:
Dr. Anne Marie Helmenstine at:
http://chemistry.about.com/cs/demonstrations/a/aa022204a.htm and
http://www.hometrainingtools.com/articles/metals-iron-conductivity-science-projects.html
