Introductory Lessons on Galvanic Cells

Cells are an abstract concept to introduce in middle school classrooms. So, lessons must be accompanied by practical explanation which supports the theory. Lessons on galvanic cells are not an exception. This lesson plan on Galvanic cells introduces students to the basic concepts about galvanic cells.

Galvanic cells, which generate electricity through the chemical reactions, are named after Luigi Galvani. He was a famous scientist in the 18th century who made the first observation on the formation of electric energy through chemical reactions. Each galvanic cell has two half cells which are connected by a salt bridge. Each half-cell is composed of a metal electrode which is immersed in a salt solution of the same metal. One of the metals acts as the anode where oxidation occurs and thus it becomes negatively charged. The other metal electrode acts as the cathode where reduction reaction happens and it becomes positively charged. The two cells are connected externally through electric wires to a voltmeter and internally through salt bridge. The salt bridge completes the circuit by acting as path for the flow of anions while at the same time keeps the two salt solutions from mixing.

Materials:

• Copper plate
• Zinc plate
• Salt solutions of zinc and copper like zinc (II) nitrate, copper (II) nitrate
• Voltmeter
• Ammeter
• Filter paper Sodium nitrate solution (saturated)
• Emery cloth
• Glass beakers of same size
• Crocodile clips
• Wires

Procedure:

• Begin the class by outlining the chemistry behind the galvanic cells and instruct students to see the activity and write down their observation.
• Clean the copper and zinc plates with the emery cloth so that there is no dirt or other material in it.
• Take one beaker and fill it half with salt solution of copper and the other beaker with salt solution of zinc. Immerse copper plate in copper solution and zinc plate in zinc solution.
• Connect crocodile clips on two ends of each wire. Place both the glass beakers adjacently. Take one of these wires and connect its one end to copper plate and other end to the voltmeter. Repeat the same with zinc plate. Now both the electrodes are connected through the voltmeter.
• Instruct your students to check the voltmeter readings and write it down. Now connect the ammeter in the place of the voltmeter and instruct your students to repeat the above activity.
• Take the filter paper and immerse it in the saturate sodium nitrate solution. Carefully remove it from the solution and slowly immerse one end of it in the zinc (II) nitrate solution and the other end in the copper (II) nitrate solution.
• Instruct the students to check the readings of ammeter. Connect the voltmeter and record the readings. If the voltmeter readings show a negative measurement then reverse the connections in the voltmeter so that the needle deflects in the positive direction.

From the first observation they will notice that neither ammeter nor voltmeter shows any readings. Whereas, on placing the soaked filter paper, both ammeter and voltmeter needles moved. From this observation they will understand that the salt bridge is a must for the proper functioning of galvanic cells. Keep the galvanic cell as such for one or two hours. This will help students to understand the changes occurring to (omit) the electrode as one gains and the other lose electrons. These lessons on galvanic cells outline the basic principle behind the galvanic cells. While teaching this lesson care should be taken so that the not even a small amount of chemicals spill on children.