Published by Australian Academy of Science
Activity 1 | Fuelling the 21st century

Making a simple electrochemical cell

Electrochemical cells convert chemical energy into electrical energy. Fuel cells are a type of electrochemical cell.

Materials (for each small group)

• piece of zinc (about 8 cm x 1 cm)
• piece of copper (about 8 cm x 1 cm)
• emery paper
• distilled water (about 40 mL, for rinsing)
• 25 mL of 0.1 M zinc (II) nitrate in a 50 mL beaker
• 25 mL of 0.1 M copper (II) nitrate in a 50 mL beaker
• ammeter (centre-zero, 0-1 milliamps with 2 leads each with an alligator clip at the free end)
• filter paper strip (about 8 cm x 1 cm)
• saturated solution of sodium nitrate (to make salt bridges)

Procedure

Safety notes:

• Do not allow any solution to come into contact with your mouth or eyes.

• Notify your teacher immediately if a spill occurs.

Set up the equipment as follows:

1. Rub the surfaces of the piece of zinc and the piece of copper with emery paper then rinse with distilled water.

2. Place the piece of zinc into the zinc (II) nitrate solution.

3. Place the piece of copper into the 25 mL of copper (II) nitrate solution.

4. Place the beakers side by side making sure the zinc and copper are NOT touching.

5. Connect the alligator clip of one lead to the zinc; connect the alligator clip of the other lead to the copper.

6. Observe the ammeter needle.

7. Carefully immerse the filter paper strip in the saturated solution of sodium nitrate.

8. Suspend the wet filter paper so that one end is immersed in the zinc (II) nitrate solution and the other is immersed in the copper (II) nitrate solution. This will form a salt bridge. (Make sure that both ends of the strip are immersed.)

9. Observe the needle on the ammeter.

• Was there a difference in the ammeter reading before and after you added the salt bridge? Explain your answer.

Teachers notes

Safety notes

Make sure students read the safety notes outlined at the beginning of the activity. Ideally, students should wear safety glasses to protect against splashing of chemicals.

Preparation

To prepare 1 litre of 0.1 M zinc nitrate: weigh 24.3 grams of Zn(NO₃)₂-3H₂0 and add distilled water to make 1 litre. (For Zn(NO₃)₂-6H₂O, weigh 29.7 grams and add distilled water to make 1 litre.)

To prepare 1 litre of 0.1 M copper nitrate: weigh 24.2 grams of Cu(NO₃)₂-3H₂O and add distilled water to make 1 litre.

To prepare a saturated solution of sodium nitrate: dissolve approximately 900 grams of NaNO₃ in 1 litre of distilled water.

Background information

Before the salt bridge is in place, there should be no ammeter deflection - no current flow. After the salt bridge is added there should be current flow.

Electron flow is from zinc to copper. (Electrons are taken from the more reactive metal, zinc.)

The potential difference between the electrodes of an electrochemical cell when no current is drawn from the cell is called the electromotive force (emf). You can measure the force of the electrochemical cell by replacing the ammeter in this activity with a voltmeter. Connect one terminal of the voltmeter to the zinc, and the other terminal to the copper. If the voltmeter is deflected in the negative direction, reconnect the leads so that a positive scale reading is obtained. The emf of the cell should be about 1.1 volts.