To show the properties of metal and the process of wet chemical plating through the process of plating a penny in zinc then heating it up to form a brass alloy.
Materials:
250mL beaker
400mL beaker
Bunsen burner
Hot plate
Tongs
Pre-1982 penny (cleaner is better)
Reagents:
Granular zinc (Zn(s))
3M Sodium hydroxide (NaOH)
Hazards and PPE:
Sodium hydroxide is corrosive to metals and can cause skin burns, particularly when heated. Handle with extreme care.
Wear approved safety goggles and gloves.
Protocol:
Preparation
Pour 200mL 3M NaOH into the 400 mL beaker.
Pour 100mL DI H2O into the 250mL beaker.
Place the beaker on the hot plate and heat over medium-high heat. Do not allow to boil.
Add 5g Zn(s) to the beaker.
Demonstration
Place penny in beaker and stir for 4 minutes.
Using tongs, remove penny from NaOH solution and place in beaker of water.
Remove penny from the water and rub with a paper towel to achieve a shiny silver look. The penny is now zinc plated.
Using the tongs, place the penny in the flame of the Bunsen burner, slowly moving it back and forth across the flame.
The heat will cause the zinc and copper atoms to mix forming a brass alloy, making the penny gold.
This step can also be achieved by simply setting the penny on the hot plate.
Additional Notes:
The penny used must be from before 1982 due to the differences in composition of pennies. From 1962 to 1981, pennies were composed of 95% copper and 5% zinc. Where pennies from 1982 and after are comprised of 97.5% zinc and 2.5% copper.
The process in this demo is one that was historically used by alchemist to try to fool people into believing they could change common metals into gold.
Disposal:
The remaining solution should be placed in a properly labeled waste container.
