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TE Activity: Two-Cell Battery

In this hands-on activity, students build their own two-cell battery. They also determine which electrolyte solution is best suited for making a battery.

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.

Learning Objectives
Materials
Introduction/Motivation
Vocabulary
Procedure
Attachments
Safety Issues
Troubleshooting Tips
Assessment
Extensions
Activity Scaling
References

Grade Level: 4 (3-5)	Group Size: 3
Time Required: 60 minutes	Activity Dependency : None
Expendable Cost Per Group : US$ 3.50
Keywords: electricity, battery, circuit, current , voltage, electrolyte, ammeter

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Colorado Math
- 1. know, use, describe, and estimate measures of length, perimeter, capacity, weight, time, and temperature; (Grades 0 - 4) [2005]
- 1. construct, read, and interpret displays of data including tables, charts, pictographs, and bar graphs; (Grades 0 - 4) [2005]
Colorado Science
- Standard 1: Students understand the processes of scientific investigation and design, conduct, communicate about, and evaluate such investigations. (Grades 0 - 12) [1995]
- 2.1 Students know that matter has characteristic properties, which are related to its composition and structure. (Grades 0 - 12) [1995]
- 2.2 Students know that energy appears in different forms, and can move (be transferred) and change (be transformed). (Grades 0 - 12) [1995]

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
1 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; see Procedure section)
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
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
Paper towels (optional)

Before starting the activity, ask students to brainstorm: From where does electricity come? (Answer: A wall outlet, power plant, photovoltaic/solar cells, batteries, etc.) If no student mentions a battery, ask the students: 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?

Next, ask students to brainstorm what is inside a battery that helps produce current electricity? (Possible answers: Chemicals, paste or a bunch of electrons.) Explain to students that inside a battery there are two metal plates or posts called electrodes where chemical reactions take place and produce electrons. There is also a solution called an electrolyte, which allows charge to move in the solution and balances the movement of electrons. Tell students that during the activity they will build their own two-cell battery and learn how engineers determine what type of electrolyte is best to use in a battery!

Show students a battery. Ask the students: 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). Let students know that during this activity they will learn how to determine the number of volts a battery produces.

You may want to remind students that 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.

Explain to students that engineers conduct research to improve the efficiency of rechargeable batteries. Battery 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. Engineers also are developing an extremely small battery that will fit in microelectromechanical systems (MEMS). MEMS devices, which will be used in medical and aerospace industries, are smaller than the width of a human hair and batteries will be needed to power these devices.

Background

A typical wet-cell battery has two terminals, a liquid electrolyte and two electrodes, called the anode and the cathode.

During this activity students make their own two-cell batteries with aluminum and copper electrodes immersed in a prepared electrolyte solution. We use two cells connected in series (one after the other) to make this battery because the voltage produced by each cell is so low; connecting the two cells in series doubles the voltage produced.

In each cell, the aluminum foil serves as the anode. The aluminum foil oxidizes, producing aluminum cations (Al³⁺) that go into the solution and leave the aluminum electrode with excess electrons. These electrons move through the foil in container A, up to the copper wire (which is connected to the ammeter), and through the ammeter to the coiled copper wire in container B.

In each cell, the copper wire is the cathode. Electrons combine with copper cations in the solution and form elemental copper. The same oxidation process takes place at the aluminum anode in container B as was described for container A. Therefore, there is a movement of electrons from the foil in container B through the copper wire to the coiled wire in container A. Again, these electrons combine with the copper cations in the solution in container A. The electrolyte in both cells serves to balance the movement of electrons by providing ions. Each cell produces a voltage of about 2 V, so the total voltage for the battery is about 4 V.

Before the Activity

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):

Weak solution: 5 ml (~1 teaspoon) of [vinegar or citrus juice or salt] for every 100 ml water
Medium solution: 15 ml (~1 tablespoon) of [vinegar or citrus juice or salt] for every 100 ml water
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 will use the weak solution, one will use the medium solution, and one will use 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.

With the Students

Have each team construct their two-cell battery at a desk. After all the teams have finished, have the class gather around the battery testing station to observe what happens when electrolyte is added to each team's battery.

Constructing the Battery:

Put a piece of tape on each glass container. Label one container A and the other B.
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.
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.
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).
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.

A photograph shows the bottom of a glass jar containing a rolled aluminum foil column bent at a 90-degree angle across the bottom of the jar. Past the bend, some of the foil is crumpled against the bottom of the glass jar. On top of the crumpled aluminum foil is an upside down paper cup bottom.

Figure 1. The aluminum foil column (anode) crumpled at the bottom and covered by a paper cup bottom.
click for copyright

Coil about 22-24 in (55-60 cm) of the 31.5 in (80 cm) 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.
Coil about 22-24 in (55-60 cm) of the second 31.5 in (80 cm) piece of wire into a ball. Place this ball on top of the paper cup bottom in container A. Make sure the copper wire is not touching the aluminum foil.
Carefully wind the free end of the third piece of copper wire (the 31.5 in wire in container A) around the top of the foil roll in container B. Again, make a couple winds with the wire to get a good connection.

Figure 2. Activity set up: A completely assembled battery ready for testing.
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Testing the Battery. Repeat steps 9-15 for each team.

Have students put on goggles when they test their battery.
Connect the free end of the wire from container A to one of the ammeter connections.
Connect the free end of the wire from container B to the other ammeter connection.
Obtain an electrolyte solution. Pour about 50 ml of the electrolyte solution into container A and about 50 ml of the same solution into container B. The solution should cover the wire coils in both containers completely; if not, carefully add more of the solution.
Measure the current produced by the battery using a DC ammeter. Have one student from each team record the electrolyte concentration and current.

A photograph displays the completed battery (described in Figure 2) being tested with a lemon juice/water electrolyte solution. Container A and container B are filled with just enough of the electrolyte solution to cover the coiled copper wire. An ammeter is connected to the two copper wires that are wrapped around the top of the aluminum foil columns. The ammeter reads 0.06 Amps.

Figure 3. The current generated by an approximate 4mL/100mL solution of lemon juice.
click for copyright

Disconnect the wires from the ammeter.
Pour the electrolyte solution back into its correct source container.
After all the students have tested their batteries, have each team disassemble their battery. Have one member of each team take their materials to the Cleaning Station. Students should gently rinse containers A and B with a small amount of water. Pour this water in the sink or into a container provided for this purpose.
Have each team report the electrolyte concentration and current produced by their battery on the board.
In teams, have students complete the Two-Cell Battery Worksheet.
As a math exercise, using the chart on the Two-Cell Battery Worksheet, have students construct a graph of current as a function of concentration and use the graph to predict what the current might be at intermediate electrolyte concentrations.

Make sure students 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 (which is a low-resistance connection established by accident between two points in an electric circuit, causing the current to flow through the area of low resistance [aluminum to copper wire] and bypass the intended circuit [the solution]). If a short circuit is created the students will not get any current reading (0.00 A) or will not obtain an accurate current reading on the DC ammeter for the solution.

Be sure to prepare enough electrolyte solution. Some containers may need up to 200 mL of solution, depending on their size.

Pre-Activity Assessment

Brainstorming: In small groups, have the students engage in open discussion. Remind students that in brainstorming, no idea or suggestion is "silly." All ideas should be respectfully heard. Encourage wild ideas and discourage criticism of any ideas. Ask the students:

From where does electricity come? (Possible answers: A wall outlet, power plant, photovoltaic/solar cells, batteries, etc.)
What is inside batteries that helps produce current electricity? (Possible answers: Chemicals, paste, or a bunch of electrons.)

Activity Embedded Assessment

Question/Answer: Ask students questions and have them raise their hands to respond. Write answers on the board and discuss as a class.

What causes the needle to move on a DC ammeter? (Answer: Chemical energy in the battery is converted to electrical energy in the copper wire, which causes the needle to move on a DC ammeter.)

Worksheet/Pairs Check: Have one student from each team record on the board the electrolyte concentration and current while using the DC ammeter. Have students work in groups to answer questions on the Two-Cell Battery Worksheet. After student teams finish their worksheets, have them compare answers with a peer group, giving all students time to finish their worksheets.

Post-Activity Assessment

Question/Answer: Ask students questions and have them raise their hands to respond. Write answers on the board and discuss as a class. Ask the students:

Explain the role of the aluminum foil and copper wire in the battery circuit. (Answer: Copper and aluminum are the electrodes in the battery. Chemical reactions take place at the electrodes producing electrons that move through the wires.)
Was there an ammeter reading for the battery before you added electrolyte? (Answer: No. There is no ammeter reading for the battery until you add the electrolyte.)
Which electrolyte solution produced the highest current reading? (Note: This depends on which electrolytes you use and on their concentration. Using a strong salt solution should give the highest current. A strong vinegar solution will produce the next highest current.)
Why do we need an electrolyte in a battery? (Answer: The electrolyte allows charge to move in the solution balancing the movement of electrons.)

For lower grades, conduct the activity as described, but do not completes the Two-Cell Battery Worksheet. Instead, have students measure and record the battery current for each electrolyte using a DC ammeter. Then, have 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 Two-Cell Battery Worksheet, and construct a graph of current as a function of electrolyte concentration. Use the constructed 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.

Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder Xochitl Zamora Thompson, Sabre Duren, Joe Friedrichsen, Daria Kotys-Schwartz, Malinda Schaefer Zarske, Denise Carlson © 2004 by Regents of the University of Colorado.
The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation GK-12 grant no. 0226322. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.

Last Modified: April 27, 2006