Have you ever wondered?
Why some pennies are shiny and other pennies are dull? Pennies are shiny when they are new but get dullerwith age.
What you will do –
Discover ways to make the penny shiny again.
Materials needed: (Get these things together first)
Your science journal
3 dull looking pennies (not shiny ones)
Piece of paper
Pencil
vinegar
salt
water
4 cups (any small cup will be good, including bathroom cups, paper cups, plastic cups, glass cups)
plastic spoon
paper towels
What you do:
You will test ways of removing the dull coating to make the penny shiny again.
1. Put about a ½ inch of vinegar in the first cup. Place the cup on your paper next to the word vinegar. This is to remind you what is in your cup. ( A V will also work, to remind you it is Vinegar)
2. Put about a ½ inch of water in the second cup. Place the cup on your paper next to the word water beside it. This is to remind you what is in your cup. ( A W will also work, to remind you it is Water)
3. Make some salt water by adding about ½ inch water in the third cup and add a spoon of salt to it and stir. Place the cup on your paper next to the words water + salt beside it. This is to remind you what is in your cup. ( W +S will also work, to remind you it is Water plus Salt).
4. Put about a ½ inch of vinegar in the fourth cup. Add a spoon of salt to it and stir. Place the cup on your paper next to the words vinegar plus salt beside it. This is to remind you what is in your cup. ( V +S will also work, to remind you it is Vinegar plus Salt)
5. Predict which liquid(s) will make the penny shiny again. If more than one, which will work fastest?
6. Place a dull penny in each cup and observe for three minutes.
7. Remove each penny, one at a time, rub with paper towel, and then rinse with water before putting the penny on the paper next to its cup.
JOURNAL:
Write what you observed when you removed the penny from the solution. Was it shiny or still dull? Was there any color left on the paper towel after you rubbed it with the penny? If yes, what was the color of left behind?Which solution did the best job of cleaning the penny?
Extension:
Try other liquids you have in your house.
You might try things like coke, sprite, coffee, milk… There are a lot of choices.
Fun Facts about pennies:
Until 1982, the composition of U.S. pennies was 95% copper and 5% zinc. By that time the value of copper had increased to the point where the penny was worth more than one cent. Since zinc is less expensive than copper, the composition of the penny was changed in 1982 to 97.5% zinc with a 2.5% coating of copper.However, a penny now costs 2 cents to produce so attention is again focused on how to produce pennies cheaper, or even the possibility of eliminating the use of pennies For example, Canada has withdrawn the Canadian penny from circulation.
Since 1982, Jarden Zinc Products, located in Greenville, Tennessee, has supplied the penny blanks – the zinc metal discs that become pennies after being coated with copper. Since the outside coating of the penny is copper, the penny looks like copper metal and has the properties of copper metal.
A new shiny penny gets dull looking after a few years.
Explanation for more mature folks – what is really happening?
The dull color is caused by a coating of copper oxide. 2Cu+O2–>2CuO
When sodium chloride dissolves in water, the sodium ions and chloride ions are free to move around. As a result, electron transfer can occur easily. Vinegar is a 5% solution of acetic acid, which is a weak acid and slowly dissolves the copper oxide coating to give Cu2+ ions and oxide ions.The chloride ions in solution do not bond strongly to Cu2+ ions, but do bond strongly to Cu+1 ions. In vinegar solution, the Cu2+ ions react with Cu atoms on the surface of the penny to give Cu+1 ions. Although this reaction is very slow in vinegar, the chloride ions in the vinegar/salt solution bond to the Cu+1 ions to form [CuCl2]-1. Therefore, the sodium chloride can be regarded as a catalyst because it speeds up the reaction of vinegar with copper oxide on the surface of the penny. Salt solution doesn’t work by itself because acid is needed to produce Cu2+ ions in solution.