Materials Included In Kit

Additional Materials Required

Safety Precautions

Sodium hydroxide is a corrosive liquid, is dangerous to the eyes; skin burns are possible. Review the Material Safety Data Sheets before beginning this activity. Wear chemical splash goggles, chemical resistant gloves and a chemical-resistant apron. Please consult current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The sodium hydroxide solution should be disposed of according to Flinn Suggested Disposal Method #10.

Teacher Tips

• Running the experiment with distilled water at first expresses the need for a catalyst in some reactions. Deionized water can be used in the first part.
• Preparation of the “electrolysis water” is simply making a 1 molar solution of sodium hydroxide (40 g/1000 mL of solution).
• Be sure to use fresh batteries or a 9-V DC transformer. Using battery holders or connector cords may make connecting the battery to the electrolysis apparatus easier.
• To construct electrodes, see the Dual-Tube Electrodes part of the Procedure.

Sample Data

Answers to Questions

1. What is the volume ratio of the gases (hydrogen and oxygen) collected?

   There is about twice as much hydrogen gas being produced as there is oxygen gas.

2. Testing of the Smaller Quantity of Gas: Describe your observations. What gas is it? What color is this gas?

   The glowing splint glows brighter for a moment. The gas is colorless. The gas is oxygen.

3. Testing of the Larger Quantity of Gas: Describe your observations. What gas is it? What color is this gas?

   The glowing splint does not glow any brighter. The gas is colorless. The gas is hydrogen.

4. Collecting and Testing of a Mixture of Hydrogen and Oxygen Gases: Describe your observations.

   In both tests, there is an explosion (popping sound) when a flaming splint or toothpick is brought close to the mouth of the tube.

5. With the use of electricity, what was learned about the composition of water?

   Answers will vary from student to student; however, in general, oxygen and hydrogen gases are produced, there is about twice as much hydrogen produced as oxygen and, finally, oxygen supports combustion.

Introduction

The decomposition of a compound into simpler substances by means of an electrical current is called electrolysis. During the electrolysis of water, electricity is passed through water which separates water molecules into hydrogen and oxygen gases.

Concepts

• Electrolysis
• Decomposition of water
• Catalysts

Materials

Safety Precautions

Sodium hydroxide is a corrosive liquid, is dangerous to the eyes; skin burns are possible. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

Note: Before beginning lab, refer to the Dual-Tube Electrodes Procedure to make dual tube electrode.

Electrolysis of Pure Water

1. Obtain a plastic cup half full of distilled water.
2. Fill the two gas collecting tubes of the electrolysis apparatus with distilled water (see Figure 1).
   {12572_Procedure_Figure_1}
3. Place the tubes into the plastic cup and connect the electrodes from the two tubes to a 9-volt DC battery (see Figure 2). Record your observations.
   {12572_Procedure_Figure_2}

4. Discard the distilled water from the previous trial.
5. Repeat steps 1–3, except this time use a 1 M sodium hydroxide solution instead of distilled water. Record your observations.

6. Continue collecting the gases until one of the two collecting tubes is filled with gas.
7. Immediately disconnect the wires from the battery. Seal the ends of both tubes with your fingers and remove from the plastic cup. One end of the tube will be sealed with the cork, the other end with your finger.
8. Mark the level of the gas in the tube containing the smaller quantity of gas. Record your observations.

9. With both collecting tubes still sealed with your finger and the cork end of tube facing down, bring the tubes to a flame.
10. Remove your finger ONLY from the tube containing the smaller quantity of gas and quickly place a glowing toothpick into the gas. A glowing toothpick has no flames, only red embers. Record your observations. Was this gas hydrogen or oxygen?

11. Unseal the other tube of gas and quickly place a glowing toothpick into this gas. Record your observations. Was this gas hydrogen or oxygen?

1. Once again fill the two gas collecting tubes with water from the plastic cup and begin to collect the hydrogen and oxygen gases.
2. When the collecting tube that is filling faster is ⅔ filled with gas, switch the wire connected to the positive terminal of the battery to the negative terminal of the battery, and that connected to the negative terminal to the positive terminal. Continue running the current until the tubes are filled with gas.
3. Disconnect the wires from the battery. Seal the ends of both tubes with your fingers and remove from the plastic cup. With both collecting tubes still sealed with your fingers, bring the tubes to a flame. Caution: Hydrogen and oxygen form explosive mixtures. Follow the directions of your teacher when testing this mixture.
4. Unseal only one of the tubes of gas and carefully place a flaming toothpick at the mouth of the tube.
5. Repeat with the other tube of gas. Record the observations.

1. Insert a pin, such as a T-pin, through each #00 cork to form a passageway for the copper wire electrode. Note: DO NOT insert the entire pin through the cork but just enough so that the pin’s point barely exits the other end of the cork. Doing this will help reduce the chances of the hole being too big, thereby causing leakage of the liquid or gas (see Figure 3).
   {12572_Procedure_Figure_3}
2. Remove the T-pin and insert a 12-cm long copper wire electrode through the hole in the cork so about 4 cm of wire protrudes from the wider end of the cork (see Figure 4).
   {12572_Procedure_Figure_4}
3. Reinsert the T-pin through the wider end of the cork just enough so that the pin’s point barely exits the other end (narrower end/electrode end). Finally, wrap the shorter protruding wire around the T-pin (see Figure 5). Do not solder the wire to the T-pin—just wrap the wire around the T-pin. Then give the wire (electrode end) a tug to tighten the connection between the wire and the T-pin.
   {12572_Procedure_Figure_5}
4. Prepare two of these electrodes and insert them into the dual tube (see Figure 6)
   {12572_Procedure_Figure_6}

Student Worksheet PDF

12572_Student1.pdf