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Types of Reactions Lab Demonstration (continued)
Background Information, Activity Setup:
I typically do this lab during a chemical reactions unit after we have learned how to balance and classify reactions. I usually set
up lab stations on cafeteria trays containing a test tube rack, test tubes, dish soap, food coloring, dropper bottles of KI, dropper
bottles of 3M HCl, 25 mL Erlenmeyer flask, and a 400 mL beaker.
Step-by-Step Procedure:
1. DEMO: Magnesium reacts with oxygen gas to produce magnesium oxide.
2. Lead(II) Nitrate: Lead(II) nitrate reacts with potassium iodide to produce lead(II) iodide and potassium nitrate.
a) Place 10 drops of potassium iodide into a test tube.
b) Add 4 drops of lead nitrate.
3. Hydrogen Peroxide: Hydrogen peroxide (H2O2) decomposes to produce oxygen gas and water.
a) Place 1 mL of hydrogen peroxide in a 25 mL Erlenmeyer Flask.
b) Place flask inside 400 mL beaker
c) Add 2 drops of dish soap and 2 drops of food coloring.
d) Add 5 drops of potassium iodide (it's used as a CATALYST to speed up the reaction).
4. Magnesium and HCl: Magnesium reacts with hydrochloric acid to produce magnesium chloride and hydrogen gas.
a) Place about an inch of hydrochloric acid into a test tube.
b) Drop magnesium into test tube
c) Wait 30 seconds then hold lit wooden split over top of test tube to perform the Burning Splint Test.
Safety Tips:
• Use a piece of steel wool or emory cloth to carefully remove the outer, dull gray oxidized layer from the magnesium ribbon.
This reduces "misfires" when it is ignited.
• Use a large, thin piece of material—such as fadeless paper or a bedsheet to block the burning magnesium from direct view.
Or, have students view it in the reflection of a fume hood.
Expected Results:
Results may vary based on materials used, setup, procedure, and other factors, however, here are a few examples on what to expect:
• Magnesium burns very bright and becomes a whitish gray ash
• Lead(II) Iodine is a yellow precipitate. PLEASE NOTE: LEAD IS TOXIC! DO NOT PUT DOWN SINK! I typically collect all the PbI2
in a container and let the water of evaporate…once the container is full—have it picked up by a chemical supply company.
• H2O2 should get hot and bubble over into the 400 mL beaker
• H2 should make a popping sound. The reaction is exothermic as well.
Teaching Notes:
• Magnesium burns really hot and needs to be lit with a Bunsen burner.
• Wait a few seconds on the Mg + HCl for enough H2 gas to build up…it will make a "pop" sound with the lit wooden splint.
