Chemistry
Decomposition Reaction-Electrolysis of Water
Introduction:
Demonstrate the decomposition of water in simple but very colorful and dramatic fashion on an overhead projector.
Concepts:
• Decomposition reaction • Oxidation–reduction • Electrolysis • pH
Materials:
Sodium Chloride/universal indicator solution, NaCl, 25 mL
Overhead projector
Pencil lead, 0.7 mm
Battery lead with alligator clips
Petri dish, disposable
Battery, 9-Volt
Graduated cylinder, 25- mL
Safety Precautions: Universal indicator is an alcohol-based solution and is flammable; do not use near an open flame. Wear chemical splash goggles, chemical-resistant gloves, and a chemical-resistant apron. Please review current Material Safety Data Sheets for addi-tional safety, handling, and disposal information.
Procedure:
1. Place the two halves of a Petri dish on the projection stage of an overhead projector. Pour enough sodium sulfate solution into each half of the Petri dish to just cover the bottom of each half dish.
2. Add 2–3 mL of universal indicator to each solution to give each a rich, transparent green color.
3. Break a pencil lead in half. Attach the leads to opposite sides of the Petri dish bottom with the alligator clips. Make sure the tip of each lead is submerged in the green solution and the alligator clips remain out of the solution.
Note:
The solution in the Petri dish top will serve as a control.
4. To start the demonstration, clip the 9-volt battery into the snaps on the battery cap (Figure 1).
5. Let the demonstration run for 5–10 minutes and note the changing colors over time and the production of gases (bubbling) at each electrode. A deep purple color forms immediately at the negative electrode, while at the positive electrode a red- orange color appears more slowly. Over time, a wider range of universal indicator colors—purple, blue, green, yellow, and red—may develop
Introduction:
Demonstrate the decomposition of water in simple but very colorful and dramatic fashion on an overhead projector.
Concepts:
• Decomposition reaction • Oxidation–reduction • Electrolysis • pH
Materials:
Sodium Chloride/universal indicator solution, NaCl, 25 mL
Overhead projector
Pencil lead, 0.7 mm
Battery lead with alligator clips
Petri dish, disposable
Battery, 9-Volt
Graduated cylinder, 25- mL
Safety Precautions: Universal indicator is an alcohol-based solution and is flammable; do not use near an open flame. Wear chemical splash goggles, chemical-resistant gloves, and a chemical-resistant apron. Please review current Material Safety Data Sheets for addi-tional safety, handling, and disposal information.
Procedure:
1. Place the two halves of a Petri dish on the projection stage of an overhead projector. Pour enough sodium sulfate solution into each half of the Petri dish to just cover the bottom of each half dish.
2. Add 2–3 mL of universal indicator to each solution to give each a rich, transparent green color.
3. Break a pencil lead in half. Attach the leads to opposite sides of the Petri dish bottom with the alligator clips. Make sure the tip of each lead is submerged in the green solution and the alligator clips remain out of the solution.
Note:
The solution in the Petri dish top will serve as a control.
4. To start the demonstration, clip the 9-volt battery into the snaps on the battery cap (Figure 1).
5. Let the demonstration run for 5–10 minutes and note the changing colors over time and the production of gases (bubbling) at each electrode. A deep purple color forms immediately at the negative electrode, while at the positive electrode a red- orange color appears more slowly. Over time, a wider range of universal indicator colors—purple, blue, green, yellow, and red—may develop