Do you ever look at that change in your pocket, particularly coins? Sometimes you get lucky enough to get a newly minted coin that’s nice and shiny. Do you ever wonder why those other coins looked darker? The copper atoms in the coin are attracted to the oxygen atoms in the air to form copper oxide. The coins look dull and dirty because they are covered with copper oxide. We are goingto try an experiment to see if we can clean the copper oxide.
What You Need:
❑ 20 dull and dirty copper coins
❑ ¼ cup white vinegar
❑ 1 teaspoonful of salt
❑ A clear shallow bowl (not metal)
❑ Paper towels
❑ Spoon
What You Do:
- Put the salt and vinegar into the bowl and stir until it dissolves.
- Put the coins into the bowl for about 5 minutes. Watch them when they first go in. What do you see?
- Take half the coins out and place them on a paper towel.
- Take the second half out and rinse them off very well. Place them on a paper towel and mark it as being “rinsed”.
- Wait about an hour and then check back on your two piles. What differences are there between the two? Record the differences and make some guesses about why they are different. The rinsed coins will be bright and new-looking.
What Happened?
When vinegar and salt dissolve the copper oxide, they make it easier for the copper atoms to join with the oxygen in the air and the chlorine in the salt. When the coins are not rinsed, it allows the chemical reaction to occur. This makes up a compound called malachite which is what coats the dark coins.
