Gold Pennies (Demo)
Pennies are turned to silver and gold.
Reference: “Chemical Demonstrations, Volume 1,” by Lee R. Summerlin and James L, Ealy, Jr., Second Edition, American Chemical Society: Washington, 1988; p. 137.
Place 5 grams of zinc dust in a beaker.
Add 6M NaOH (24 g NaOH / 100 ml water) to cover the dust thoroughly.
Heat the solution to almost boiling by using a hot plate.
Prepare a penny (minted before 1983) by cleaning with steel wool.
Using tongs, place the cleaned penny in the hot solution and heat for 3-4 minutes.
Remove the silver penny, rinse with water and pat dry with paper towels.
Using tongs, place the penny directly on the hot plate.
Remove from hot plate as soon as it turns gold, rinse and dry.
Explanation: The silver coating on the penny is plating of sodium zincate. The heat causes a fusion between copper and zinc to form the brass alloy.
Tips:
Magnesium Burn (Demo)
Magnesium ribbon is burned in air.
Reference: “Chemical Demonstrations, Volume 1,” by Bassam Z. Shakhashiri, University of Wisconsin Press: Madison, 1983; p. 38.
Procedure: Light a burner and adjust the flame to light blue.
Hold a piece of magnesium ribbon with tongs.
Place the ribbon into the flame until it ignites.
Do not look directly at the burning ribbon as the light is bright enough to cause harm.
Explanation: The magnesium needs lots of energy to start combustion but more is given off once the reaction has started. Approximately 10 percent of the energy produced is given off as light.
Tips:
Zinc to Copper (Hands-on)
Zinc is changed to copper in a solution.
Reference: “Chemical Activities,” by Christie L. Borgford and Lee R. Summerlin, Teacher Edition, American Chemical Society: Washington, 1988; p. 119.
Fill a test tube two-thirds full with a 1M CuSO4 solution (25 g CuSO4·5H2O / 100 ml water).
Add the required granular zinc or zinc powder to the test tube according to the ratio of 25 ml of solution to 2 grams of zinc.
Stopper the flask and shake vigorously for 10-15 seconds.
Observe what happened.
Explanation: The reaction is exothermic and the gray solid is replaced by a brown solid. The solution will go from blue to colorless. The zinc metal is being oxidized to cations and the copper ions are being reduced to copper metal.
Tips:
Magic Penny (Demo)
The inside of a penny is reacted leaving the copper shell.
Reference: “Chemical Demonstrations, Volume 2,” by Lee R. Summerlin, Christie L. Borgford and Julie B. Ealy, Second Edition, American Chemical Society: Washington, 1988; p. 63.
“Chemical Activities,” by Christie L. Borgford and Lee R. Summerlin, Teacher Edition, American Chemical Society: Washington, 1988; p. 77.
“Chemical Magic from the Grocery Store,” by Andy S. W. Sae, Kendall/Hunt: Dubuque, 1996; p. 83.
Use a file to scrape 4-6 notches on the edge of a penny minted 1983 or later.
Make sure the notch is deep enough to reach the zinc.
Put the penny into a small beaker with 20 ml of 6M HCl.
Observe what happens.
When the bubbling stops, which may take a few hours or over night, rinse the penny with water and pat dry with a paper towel.
Pass the penny around so the students can feel it and see what it looks like.
Explanation: Hydrochloric acid dissolves many different metals, including zinc, by reacting with them to produce hydrogen gas. However, it does not react with copper. The inside of the penny is zinc metal and will disappear in the solution leaving the outer shell made of copper.
Tips:
Blazing Bubbles (Demo)
Ignite bubbles of a gas.
Reference: “Chemical Demonstrations, Volume 2,” by Bassam Z. Shakhashiri, University of Wisconsin Press: Madison, 1985; p. 128.
Obtain a 500-ml filtration flask and attach rubber tubing to the side arm.
Add 8 grams of magnesium turnings to the flask followed by 20 ml of water.
Carefully, add 40 ml of concentrated sulfuric acid and stopper the flask.
Place the end of the tubing in a soapy solution.
Light the bubbles that form in the solution with a match.
A small flame and popping noise should result.
Explanation: The sulfuric acid reacts with the magnesium to produce hydrogen gas which is forced through the tubing and forms the bubbles in the soapy solution. The match ignites the hydrogen as it comes in contact with the oxygen of the air to form water.
Tips:
Purple Flask (Demo)
A small amount of water coats the inside of a flask purple.
Reference: “Chemical Demonstrations, Volume 1,” by Bassam Z. Shakhashiri, University of Wisconsin Press: Madison, 1983; p. 49.
Using a mortar and pestle, grind 2 grams of 20-30 mesh zinc and 7 grams of iodine together until they are intimately mixed.
Attach an iron ring to a ring stand above a test tube clamp.
Mount a large test tube vertically and pour the mixture into the test tube.
Invert a round-bottom flask and support it with the ring.
Adjust the ring such that the test tube extends well into the flask and the flask touches the clamp.
With one hand lift and hold the flask; with the other hand pour 3 ml of water.
Replace the flask immediately and observe what happens.
Explanation: The water provides a medium for the reaction between zinc and iodide. The product formed is zinc iodide. This reaction gives off enough heat to sublime the iodine and the vapor forms purple deposits on the inside of the flask.
Tips: