Two Cell Battery. 6. Masking tape 7. Wire cutters 8. Vinegar 9. Salt 10. Lemon Juice DC ammeter

Transcription

1 Your Activity Build a two-cell Wet battery Materials ml beakers 2. 2 pieces aluminum foil (8 X 12 inch) 3. 2 small paper cups, cut ¾ from bottom inch of non-insulated copper wire gauge AWG Water 6. Masking tape 7. Wire cutters 8. Vinegar 9. Salt 10. Lemon Juice DC ammeter Create 1. Create the battery using the detailed instruction sheet a. Note Make sure you do not touch the copper wire and the aluminum foil. If the copper wire and aluminum foil contact each other, it produces a short circuit. If a short circuit occurs, you will not be able to obtain an accurate reading on the DC ammeter for the solution. 2. Test the battery using different solutions a. Water/Vinegar b. Water/Salt c. Water/Lemon Juice 3. Complete the worksheet Science Topics Chemistry, Chemical Reactions, Industrial Chemistry, Earth Science What s going on? The battery created in this activity is called a wet cell, or voltaic cell, because a liquid (citric acid / vinegar) is involved. Car batteries are usually wet cells. Aluminum foil and copper wire are the electrodes in this battery and a citric acid solution is the electrolyte. The aluminum foil oxidizes and positive aluminum ions go into solution, leaving an excess of electrons on the aluminum electrode. The citric acid electrolyte facilitates the electron flow. The electrolyte is needed to get a transfer of electrons. Without an electrolyte the electrons cannot move and current (amps) would not be produced. So, have you wondered what is inside the battery that helps produce electricity?

2 Activity Lead Notes Introduction Students build their own two-cell batteries. They also determine which electrolyte solution is best suited for making batteries. Students should recognize the essential parts of a voltaic (wet) cell. These include two pieces of different metals and a solution to assist in conducting electricity. The solution is called an electrolyte, which can be an acid, a base or a salt. Fruit juices and vinegar are acids, ammonia is a base and baking soda is a salt. Learning Objectives After this activity, students should be able to: Describe the energy transformations that take place when a battery is connected in a circuit. Explain that an electrolyte is needed for a battery to produce current electricity. Construct and interpret a graph of current produced by a battery as a function of electrolyte concentration. Relevance For some engineers, designing amazing batteries is their specialty. Electrical engineers continually conduct research to improve the efficiency of rechargeable batteries that are used in laptops, cell phones, digital cameras and electric cars. Some engineers are developing extremely tiny batteries that are smaller than the width of a human hair. These batteries provide power for microelectromechanical systems (MEMS) located in devices for specialized use in the medical and aerospace industries.

3 Background (Before starting the activity, ask students to brainstorm.) From where does electricity come? (Possible ideas: A wall outlet, power plant, photovoltaic/solar cells, batteries, etc. If no student mentions a battery, ask them the next question.) Do you think electricity can come from a battery? (Answer: Yes) Have you ever wondered what is inside of a battery? How do engineers decide what liquid or paste to use in this can full of chemicals? What is inside a battery that helps produce current electricity? (Possible ideas: Chemicals, paste or a bunch of electrons.) Well, inside a battery are two metal plates or posts called electrodes where chemical reactions take place and produce electrons. Also inside is a solution called an electrolyte, which allows charge to move in the solution and balances the movement of electrons. During today's activity, you will create your own two-cell batteries and learn how engineers determine what type of electrolyte is best to use in batteries! (Show students a battery.) Have you ever looked closely at a battery and seen a small number with the letter "V" next to it? What does the letter represent? (Answer: Volts) During today's activity, you will learn how to determine the number of volts a battery produces. (Remind students.) Remember when we learned about atoms...? Atoms are made of smaller parts called protons, neutrons and electrons. The electrons carry a negative electric charge, move from atom to atom, and create current electricity. How many different applications can you think of that use batteries? (Listen to student ideas.) How do you think that engineers might be involved with batteries? (Listen to student ideas.) Well, engineers design all the types of batteries that we use every day. Some engineers conduct research to improve the efficiency of rechargeable batteries. Other engineers work to improve rechargeable lithium batteries that are used for laptops, digital cameras and electric cars so they last longer and are able to be re-charged for additional cycles. Grade Level 4 Materials Each group needs: 2 pieces aluminum foil: 8 in x 12 in (20 cm x 30 cm) 2 wide-mouth glass jars (must be able to hold at least 150 ml) 2 small paper cups (such as Dixie cups), cut at ¾ in from the cup bottom, or 2 plastic caps from milk jugs 3 pieces (one: 12 in [30 cm] and two: 31.5 in [80 cm]) of non-insulated copper wire (gauge AWG 20) (available at most hardware stores); a total of 75 in (200 cm) per group. Or, if you have insulated wire, it will work if you strip the insulation off the ends. masking tape wire cutters marking pens Two-Cell Battery Worksheet For a Battery Testing Station for the entire class to share: containers for the electrolyte solutions (must be able to hold at least 150 ml); wide-mouth glass jars work well electrolyte solutions (make in advance with water and vinegar, citrus juice [such as lemon] or salt a few graduated cylinders (10-25 ml) or liquid measuring cups or jars with volumes marked on the side 3 pairs of safety glasses or goggles

4 1 DC ammeter (to measure current in amperes) (available at most hardware or electronics shops) paper towels For a Cleaning Station for the entire class to share: water and sink, or, if no drain is available, a large empty container to collect the used electrolyte solutions (optional) paper towels Preparing Materials Cut two 8 in x 12 in (20 cm x 30 cm) pieces of aluminum foil for each team. Cut one 12 in (30 cm) piece and two 31.5 in (80 cm) pieces of wire for each team. Note that insulated wire can be used, as long as it is stripped at the ends. Decide which electrolytes to use. (Suggestion: For a class of 27 students working in nine teams of three students each, use three different electrolytes [vinegar, citrus juice, salt] in three different strengths [weak, medium, strong].) Prepare the electrolyte solutions, making about 400 ml of each solution. Make sure to label them. The whole class can use the same type of solution at different strengths, or different teams can have different types of solutions at a range of strengths (see examples below): o Weak solution: 5 ml (~1 teaspoon) of [vinegar or citrus juice or salt] for every 100 ml water o Medium solution: 15 ml (~1 tablespoon) of [vinegar or citrus juice or salt] for every 100 ml water o Strong solution: 40 ml (~2.5 tablespoon) of [vinegar or citrus juice or salt] for every 100 ml water If the number of teams is not a multiple of three (one team using the weak solution, one using the medium solution, and one using the strong solution), prepare more electrolyte solutions for the remaining teams, making them incrementally stronger. Prepare a Battery Testing Station for the entire class to use: 3 pairs of goggles, a DC ammeter, graduated cylinders, all the containers of prepared electrolyte and paper towels. Set up a Cleaning Station. Make copies of the Two-Cell Battery Worksheet, one per team. Make copies of the Two-Cell Battery Detailed Instructions, one per team. Procedure Have each team construct its two-cell battery at a desk. After all the groups have finished, gather the class around the battery testing station to observe what happens when electrolyte is added to each team's battery. Construct the battery 1. Put a piece of tape on each glass container. Label one container A and the other B. 2. Have students roll each piece of foil so the long side of the roll is about 12 in (30 cm). Crumple about 1/4 of one end on each roll. 3. Place one aluminum foil roll in each container, placing the crumpled end on the bottom of the container. Carefully flatten the rolled part of the foil against the side of each container. 4. Place a paper cup bottom (or milk cap) on top of the crumpled foil in each container; the aluminum foil column should go up and around the side of the paper cup (or milk cap) (see Figure 1). 5. Carefully wind one end of the 12 in (30 cm) piece of copper wire around the top of the foil roll in container A. Make a couple winds with the wire to get a good connection. Leave the other end of the wire free. 6. Coil about inches of the 31.5 inch piece of wire into a ball. Place this ball on top of the paper cup bottom in container B. Make sure the copper wire is not touching the aluminum foil. 7. Coil about inches of the second 31.5 inch piece of wire into a ball. Place this ball on top of the paper cup bottom in container B. Make sure the copper wire is not touching the aluminum foil.

5 8. Carefully wind the free end of the third piece of copper wire (the 31.5 inch wire in container A) around the top of the foil in the container B. Again, make a couple winds with the wire to get a good connection. Test the battery 1. Have students wear goggles when they test their batteries. 2. Connect the free end of the wire from container A to one of the ammeter connections. 3. Connect the free end of the wire from container B to the other ammeter connection. 4. Obtain an electrolyte solution. a. Pour about 50 ml of the electrolyte solution into container A and about 50 ml of the same solution into container B. b. The solution should cover the wire coils in both containers completely; if not, carefully add more of the solution. 5. Measure the current produced by the battery using a DC ammeter. Have one student from each team record the electrolyte concentration and current. 6. Disconnect the wires from the ammeter. 7. Pour the electrolyte solution back into its correct source container. Measurement & Analysis 1. In teams, have students complete the Two-Cell Battery Worksheet. Takedown Clean up the experiment area and all reusable materials Return all equipment and supplies to the storage. Safety Require students to wear safety goggles at the Battery Testing Station in case any electrolyte splashes. Watch that students do not play with the copper wire, so they do not cut themselves or others. Activity Scaling For lower grades, conduct the activity as described, but do not completes the worksheet. Instead, have students measure and record the battery current for each electrolyte using a DC ammeter. Then, let them explain which electrolyte concentration produces a battery with the highest current. For higher grades, have students measure current using a DC ammeter, complete the worksheet, and create graphs of current as a function of electrolyte concentration. Use the graph to predict the current at intermediate electrolyte concentrations. Ask students to draw conclusions about how the current produced by a battery depends on the concentration of the electrolyte in the battery. Source and Additional Information TeachEngineering.org n03_activity2.xml

6 Detailed Instructions Make the battery 1. Put a piece of tape on each glass container. Label one Container A and the other Container B. 2. Have students roll each piece of foil so the long side of the roll is about 12 in (30 cm). Crumple about 1/4 of one end on each roll. 3. Place one aluminum foil roll in each container, placing the crumpled end on the bottom of the container. Carefully flatten the rolled part of the foil against the side of each container. 4. Place a paper cup bottom (or milk cap) on top of the crumpled foil in each container; the aluminum foil column should go up and around the side of the paper cup (or milk cap) (see Figure 1). 5. Carefully wind one end of the 12 in (30 cm) piece of copper wire around the top of the foil roll in container A. Make a couple winds with the wire to get a good connection. Leave the other end of the wire free. 6. Coil about inches of the 31.5 inch piece of wire into a ball. Place this ball on top of the paper cup bottom in container B. Make sure the copper wire is not touching the aluminum foil. 7. Coil about inches of the second 31.5 inch piece of wire into a ball. Place this ball on top of the paper cup bottom in container B. Make sure the copper wire is not touching the aluminum foil. 8. Carefully wind the free end of the third piece of copper wire (the 31.5 inch wire in container A) around the top of the foil in the container B. Again, make a couple winds with the wire to get a good connection. Test the battery 1. Wear goggles when you test the battery 2. Connect the free end of the wire from container A to one of the ammeter connections. 3. Connect the free end of the wire from container B to the other ammeter connection. 4. Obtain an electrolyte solution. a. Pour about 50 ml of the electrolyte solution into container A and about 50 ml of the same solution into container B. b. The solution should cover the wire coils in both containers completely; if not, carefully add more of the solution. 5. Measure the current produced by the battery using a DC ammeter. Record the electrolyte concentration and current. 6. Disconnect the wires from the ammeter. 7. Pour the electrolyte solution back into its correct source container.

7 Worksheet 1. Complete the following chart Solution # Electrolyte Concentration DC Ammeter Reading 1 Water/Vinegar 5 ml / 100 ml solution of vinegar 2 Water/Vinegar 25 ml / 100 ml solution of vinegar 3 Water/Salt 5 ml / 100 ml solution of saltwater 4 Water/Salt 25 ml / 100 ml solution of saltwater 5 Water/Lemon Juice 5 ml / 100 ml solution of lemon juice 6 Water/Lemon Juice 25 ml / 100 ml solution of lemon juice 2. What solution produced the lowest current? Why? 3. Which solution produced the highest current? Why? 4. What is the role of aluminum foil and copper wire in the battery circuit? Answer: Copper and aluminum are the electrodes 5. Why do we need an electrolyte in a battery? Answer: The electrolyte allows charge to move in the solution balancing the movements of electrons