Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Pour approximately 50 mL of solution into six 100-mL beakers. Place these beakers in a common chemical dispensing station.
2. Cut the aluminum foil into 12" x 12" pieces, enough for each lab group.

Safety Precautions

Charcoal is a flammable solid. Keep away from flames. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Be sure all circuit connectors and work surfaces are dry before conducting the experiments. Do not touch any part of the circuit with wet hands. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Sodium chloride solution may be disposed of according to Flinn Suggested Disposal Method #26b. Activated charcoal may be disposed of in the trash according to Flinn Suggested Disposal Method #26a. Alternatively, the charcoal may be saved, dried and stored for future use.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. This lab can be completed in one 50-minute class period.
• Save the charcoal for future labs. Collect the charcoal after the lab and allow it to dry before storing in the bottle.

Teacher Tips

• If lightbulbs and sockets are available, have students attempt to light them with the Dry Cell Battery. Some questions for the students: How many batteries will it take to light the lightbulb? What is the best battery configuration (series or parallel) of lighting the lightbulb with the fewest batteries? What seems to be the most important factor to get a lightbulb to glow—the voltage or the current?

• The half reactions for the aluminum–air battery are as follows:

  Al(s) → Al³⁺(aq) + 3e^–                                        E^o = 1.66 V (oxidation half-reaction)

  O₂(g) + 2H₂O(l) + 4e^– → 4OH^–(aq)                 E^o = 0.40 V (reduction half-reaction)

  The overall cell potential is positive, which means the electron transfer reaction will be spontaneous, with a theoretical value of 2.06 V.

• Do not store the Dry Cell Batteries. The reactions will continue and slowly dissolve the metal alligator clip. Be sure to disassemble the batteries after the lab.

Sample Data

Answers to Questions

1. Define oxidation. What substance in the Dry Cell Battery is oxidized?
   Oxidation is the loss of electrons. In the aluminum–air battery, the aluminum is oxidized.
2. Define reduction. What substance in the Dry Cell Battery is reduced?
   Reduction is the gain of electrons. The oxygen in the air is reduced by the electrons supplied by the oxidation reaction of aluminum.
3. What was the purpose of the saturated salt solution?
   The saturated salt solution provides the salt bridge for the oxidation–reduction reaction between the electrodes. Without the salt bridge, charge buildup would occur and the chemical reactions would stop.
4. Describe the flow of electrons through the dry cell battery and motor circuit. What part of the battery is the anode and what part is the cathode? Refer to the Background section.
   Electrons travel from the aluminum foil anode on the outside of the battery through the circuit. The electrons travel through the motor windings and cause it to spin. The electrons then travel through the conductive wire toward the cathode (charcoal) inside the battery. At the cathode, the oxygen inside the air pockets is reduced by the electrons. Anions and cations flow through the salt bridge to the anode and cathode, respectively, to prevent charge buildup.
5. What happened when the dry cell battery was pressed down? Explain.
   When the battery was compressed, the voltage and current output increased. This may have occurred because more air made contact with the metal alligator clip inside the battery, providing more reduction sites for the electrons traveling from the aluminum foil. Note: The limiting step in this reaction is the reduction step, which depends on the amount of oxygen present on the inside of the battery and how much is in contact with the metal alligator clip.
6. How did the voltage and current change when two batteries were connected in series? What happened when the batteries were compressed?
   In series, the two batteries produced more voltage and about the same current. The voltage was about double of that produced by the single battery while the current stayed about the same. When the batteries were compressed, the current increased by a large amount and the voltage only slightly increased.
7. How did the voltage and current change when two batteries were connected in parallel? What happened when the batteries were compressed?
   In parallel, the two batteries produced more current and approximately the same voltage as a single battery. The current nearly doubled compared to the two batteries in series and the single battery. Current increased greatly; voltage increased slightly.

References

http://www.exo.net/~pauld/activities/AlAirBattery/alairbattery.html (Accessed June 2018)

Introduction

Batteries provide electricity for nearly every small electrical device in the home—from flashlights and watches to power tools. The composition of a battery depends on the purpose for which it will be used. Some batteries, such as those in an artificial pacemaker, need to operate for a very long time. Other batteries need to be reliable and ready to supply electricity at any time, even after several years of storage.

Concepts

• Battery
• Voltage
• Oxidation–Reduction
• Current

Background

A battery is an electrochemical cell known as a voltaic cell. In a voltaic cell, a spontaneous chemical reaction releases energy in the form of electricity (moving electrons). The chemical reaction that generates electricity in a battery is known as an oxidation–reduction reaction. Oxidation is a term used to describe when a substance loses electrons. Reduction describes a process in which a substance gains electrons. When a substance is oxidized and loses electrons, the resulting oxidized species becomes more positive. In a typical “wet cell” battery, the oxidized substance is converted from a neutral metal atom into a metal cation, or an ion with a positive charge. During reduction, a substance gains electrons and becomes more negative. Again, using the “wet cell” battery example, the reduced substance is a metal cation that gains electrons to become a neutral metal atom.

To create a battery that provides electrical energy, a voltaic cell must be produced. The battery must have a substance that will be oxidized at one electrode, a substance that will be reduced, and a “salt bridge” that separates the two substances. The salt bridge contains an electrolyte (dissolved ions) that allows for the flow of ions between the two substances. When the two electrodes are connected together with a conductive wire, the electrons generated at the oxidized electrode (also known as the anode) flow toward the reduced electrode (known as the cathode) along the conductive wire. In the process of moving through the wire, the electrons can provide energy to materials connected between the two electrodes. This “electron energy” is more commonly referred to as electricity. During the spontaneous oxidation–reduction reaction, excess positive and negative charges can build up on the anode and cathode side, respectively. The “salt bridge” prevents the buildup of excess charge at the two electrodes. Without the salt bridge, the charge buildup at the electrodes would prevent the oxidation–reduction reactions from continuing (see Figure 1).

The name “dry cell” battery is a slight misnomer since this type of battery is not entirely dry. A modern 1.5-volt “alkaline” battery consists of a zinc anode (a granulated zinc mixture), and a moist cathode paste consisting of carbon (graphite), manganese dioxide (MnO₂) and sodium hydroxide (NaOH). The anode and cathode are separated by a paper sheath soaked in a concentrated sodium hydroxide solution. This mixture provides a spontaneous electrochemical reaction when zinc is oxidized to generate electrons, and the manganese dioxide is reduced. The carbon electrode provides a surface on which reduction occurs. Carbon is called an inert electrode because it is not consumed during the reactions.

The dry cell battery constructed during this lab is an aluminum–air battery (see Figure 2). Aluminum foil will be oxidized at the anode, while oxygen from the air is reduced at the cathode. Activated charcoal provides the surface for reduction to occur (just as in an “alkaline” battery) and because of its very finely divided nature, resulting in many air pockets, it also supplies the oxygen. In order for the reactions to proceed, an aqueous (water) environment is needed, so the materials must be damp. A piece of electrolyte-soaked chromatography paper will be used as the “salt bridge” to separate the anode from the cathode and allow for the flow of ions.

Experiment Overview

In this activity, a simple dry cell battery will be constructed from ordinary household items. Experiments will be performed to determine the battery’s electrical properties.

Materials

Safety Precautions

Charcoal is a flammable solid. Keep away from flames. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Be sure all circuit connectors and work surfaces are dry before conducting the experiments. Do not touch any part of the circuit with wet hands. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

Dry Cell Construction

1. Obtain a sheet of chromatography paper, paper towel, pipet, and a 12" x 12" sheet of aluminum foil.
2. Place the aluminum foil sheet flat on the tabletop. Place the chromatography paper on top of the paper towel lying flat on the tabletop.
3. Obtain approximately 50 mL of saturated sodium chloride solution in a 100-mL beaker.
4. Using the disposable pipet, add the saturated sodium chloride solution to the chromatography paper lying on the paper towel. Wet the entire chromatography paper. The excess solution will be pulled through to the paper towel.
5. Using forceps, or a gloved hand, place the wet chromatography paper onto the center of the aluminum foil sheet.
6. Obtain the red connector cord with alligator clips.
7. Slide the protective plastic sheath on one of the alligator clips back towards the wire section of the connector cord to expose as much of the alligator clip as possible (see Figure 3).
   {13250_Procedure_Figure_3}
8. Place the exposed alligator clip in the center of the wet chromatography paper. Extend the connector cord along the center line of the chromatography paper as shown in Figure 4.
   {13250_Procedure_Figure_4}
9. Obtain approximately 10–15 g of activated charcoal from the chemical dispensing station. Place the activated charcoal into a weighing dish or 400-mL beaker. Note: Be careful! Activated charcoal powder will easily create a black mess on skin, clothing and the tabletop. Scoop and pour this material slowly and in small quantities.
10. Using a scoop or spatula, carefully cover the exposed alligator clip in the center of the chromatography paper with the activated charcoal (see Figure 4). Make sure the metal of the alligator clip is completely covered with the charcoal.
11. Carefully fold the aluminum foil and blotting paper into thirds, then fold the ends in (like a “burrito”) as shown in Figures 5a–5d. Note: Be sure the chromatography paper stays between the aluminum foil and the activated charcoal.
    {13250_Procedure_Figure_5}
12. Obtain the black connector cord.
13. Clip one end of the black connector cord to the aluminum foil (see Figure 5e).
14. The Dry Cell Battery is now complete.

Experiment 1. Measuring Current and Voltage

1. Obtain a digital multimeter, or a separate DC voltmeter and DC ammeter.
2. Set up the multimeter or ammeter to measure 1 amp DC.
3. Connect the connector cords from the dry cell battery to the multimeter or ammeter. Measure and record the current value in the data table. Adjust the multimeter or ammeter settings (or connections) as necessary to obtain the most accurate measurement.
4. Set up the multimeter or voltmeter to measure 1 volt DC.
5. Connect the connector cords from the dry cell battery to the multimeter or voltmeter. Measure and record the voltage in the data table. Adjust the multimeter or voltmeter settings (or connections) as necessary to obtain the most accurate measurement.
6. Repeat steps 2–5. However, during these trials, compress the Dry Cell Battery by pressing down. Measure and record the maximum current and voltage obtained by the Dry Cell Battery in the data table.

Experiment 2. Series versus Parallel

7. Pair up with another group (or, if there are enough materials, construct a second Dry Cell Battery). Connect two Dry Cell Batteries together in series (see Figure 6a).
8. Measure the current using the same procedure as Experiment 1. Record the values in the data table.
9. Measure the voltage according to the procedure in Experiment 1. Record the values in the data table.
10. Connect the two Dry Cell Batteries in parallel (see Figure 6b). Use two paper clips as the junction points for the parallel circuit. Repeat steps 8–9. Record the results in the data table.
    {13250_Procedure_Figure_6}

Experiment 3. Powering a Motor

11. Obtain a mini DC motor.
12. Connect the Dry Cell Battery to the terminals of the motor. Does the motor spin? Record the results in the data table.
13. Press down on the Dry Cell Battery. Does the motor spin? Record the results in the data table.
14. Repeat steps 12 and 13 using two batteries in series and two batteries in parallel. Record the results in the data table.
15. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

13250_Student1.pdf