Lesson 4: The Fourth physics lesson with a native speaker of English
The topic is “Daniell Cell”
- Zinc bar
- Copper bar
- Oxidation reduction reaction
- Zinc sulfate solution
- Copper sulfate solution
- To dissolve
- Moving electrons
- A salt bridge
- To pull electrons (a pull for electrons)
- Neutral atoms
- Solid metal
- To attach to = to stick to
Voltaic/Galvanic cell is a device that uses chemical reactions to create electricity. In this case the type of a chemical reaction that they use is called an oxidation-reduction reaction.
There are two containers:
1) One with zinc sulfate solution and a piece of zinc (or a zinc bar) placed into this solution. This container is called Anode.
2) The other container has copper sulfate solution with a piece of Copper (or a copper bar) in it. This container is called Cathode.
The pieces of zinc and metal are connected with a metal wire, through which electrons start moving. Moving electrons create electricity. The solutions in the containers are connected with a salt bridge.
Why do electrons move?
When you connect two pieces of metal with a wire, they start attracting each other’s electrons. Copper has a stronger pull for electrons and starts pulling them away from zinc. In this way zinc loses electrons and becomes positively charged. It changes a lot of things because neutral atoms make up a solid metal. When these atoms become positive, they are no longer a part of the solid metal but start dissolving in the solution. This is what happens in the Anode part of the cell. This chemical reaction is called Oxidation.
In the Cathode part, Copper gains electrons and becomes negatively charged. It then starts attracting positive ions from the solution and they turn into neutral atoms which can no longer be a part of the solution, but stick to the solid copper metal. This reaction is called Reduction.
Oxidation (electron loss) and Reduction (electron gain) create together what is called Oxidation-Reduction reaction.
Salt bridge is used to balance two solutions. In the anode part of the cell, a positive charge builds up and in the cathode part a negative charge builds up. To avoid building up too much of positive and negative charges in the parts of the cell a salt bridge is used.
Salt bridge has a porous structure and is filled with NaCl (Sodium Chloride) solution. Positively charged Na+ will be attracted by negatively charged copper sulfate solution and negatively charged CL- will move to positively charged zinc solution, balancing them. Otherwise, the cell will not work.
Cut two potatoes in halves and make notches in them with a knife. Then, place one of the zinc washers and one of the copper pennies into each of the potato sections. Take one of the test cables with clippers at the end and connect one end to the zinc washer and the other end to the copper penny. If you touch your multimeter cables to the pieces of zinc and copper inside the potato, you will see that it conducts electricity.
Special Thanks to Olena Shlap (native speaker of English)