- Read the MSDS sheets for sodium hydroxide and zinc before proceeding. Wear apron, goggles and gloves.
- Clean a pre-1982 penny with an eraser or steel wool (Brillo) until it is shiny OR clean chemically with 3.0 grams of table salt mixed with 15ml of vinegar and place the pennies into this solution until they are shiny on both sides.
- Place 1 gram of zinc dust into a glass dish.
- Add 3M sodium hydroxide solution to cover the zinc. 3M = 12g of NaOH/100ml of solution (slightly less than 100ml of water). You will only need about 25ml. of solution if you purchase it.
- Gently heat the zinc and solution and stir with a glass rod until it is near boiling. It should just start steaming.
- Using tongs or tweezers put the penny into the near boiling solution for about four minutes.
- Remove the penny, rinse in distilled water, dry with a paper towel (do not rub the coating off). Note the silver color.
- Using tongs or tweezers hold the penny in a Bunsen burner or propane torch flame until the gold color appears. Do not get too close with the flame as you will melt the penny. Dip into a new container of distilled water.
- Let the penny cool before taking off your gloves and handling it.
Note: Read MSDS sheets before doing this experiment. Go to the internet icon to find links to web sites that have the MSDS sheets. Pour the zinc solution into a large glass beaker and rinse the glass dish into the beaker. Add water to near the top of the beaker and let the zinc settle. Then slowly add more water until it overflows the beaker and let this continue for a few minutes to get rid of the sodium hydroxide. Pour off the excess water and collect the zinc. Let the zinc dry for later reuse or dispose of according to the MSDS sheets.
- When you added sodium hydroxide to the zinc solution you formed zinc zincate (Na2ZnO2). This reduced the penny to form a metallic zinc coating that looks like silver.
- Heating the silver penny allows the zinc to react with the copper to form brass which looks like gold. Brass is 60 to 82% copper and 18 to 40% zinc.
You can purchase the chemicals from many supply houses, but I like Flinn Scientific (http://Flinnsci.com) because you can get small volumes which reduces disposal problems.
Questions
- Show the redox equations for what occured.
- Why did the silver color occur without using the burner?
- Why did the penny need to be heated for the gold color to appear?
- What other elements are found in some brass?
- Why do pre-1982 pennies work best? Try the Coin Isotope experiment and some other chemical tests to see if there is a difference between these pennies and post-1983 pennies.
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- When you added sodium hydroxide to the zinc solution you formed zinc zincate (Na2ZnO2). This reduced the penny to form a metallic zinc coating that looks like silver.
- Heating the silver penny allows the zinc to react with the copper to form brass which looks like gold. Brass is 60 to 82% copper and 18 to 40% zinc.
- Show the redox equations for what occured.
- Why did the silver color occur without using the burner?
- Why did the penny need to be heated for the gold color to appear?
- What other elements are found in some brass?
- Why do pre-1982 pennies work best? Try the Coin Isotope experiment and some other chemical tests to see if there is a difference between these pennies and post-1983 pennies.
Back to top