Fruit Battery Teacher Kit - The Colby College Community Web

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Power Outage at the Grocery Store
Teacher’s Instructions
Description of Activity
Students will power simple devices by building voltaic cells that generates
power from reduction and oxidation reactions on two common metals, using
everyday grocery items to provide the electrolyte that maintains a charge balance
and permits the reaction to continue. Students will vary the set up and materials in
order to try and find the optimal voltage and current that can be generated from
these batteries.
Learning Goals
 Learn the essential components of a working voltaic cell battery.
 Learn to use a voltmeter to measure the voltage and current produced by a
cell.
 Understand the difference between voltage and current.
 Learn the difference between series and parallel battery set up, and the
resulting changes in voltage and current that result.
 Use scientific reasoning and observations to deduce the best materials and
conditions for creating a battery.
Recommended Grades: Grades 4-12, depending on optional added activities
Estimated Time Required: 60 minutes, can be shortened by excluding some
activities
Key Concepts and Explanation of Terms:
Voltage: The potential difference in charge between two points.
Current: The rate at which electrical charge flows past a point.
Electrode: Point at which electrons originate or flow to.
Anode: Negatively charged electrode.
Cathode: Positively charged electrode.
Electrolyte: Solvent that dissociates into ions in solution.
Redox Reactions: Reaction where involved species’ oxidation states are changed.
Reducing and Oxidizing Agents: Chemical that serves to reduce or oxidize another
substance.
What Happens and Why:
Two metals, copper and zinc, have different affinities for electrons. Zinc will
be oxidized and give electrons to copper (which is reduced) in order to achieve a
lower energy state of the system. In order for this to occur, however, the positive
charges from copper need to migrate toward the zinc. Since they cannot transfer
through a wire like the electrons can, an electrolyte “salt bridge” is needed to move
the positive charges across and keep the reaction moving. The flow of electrons, by
definition, is electricity, useful for powering items. By setting up an electrical device
in the electrical current, it can be powered by the charge flowing across the wire. A
Power Outage at the Grocery Store, CALEB HARRIS, 1/29/14
1
common misconception is that the fruit powers the batteries. In actuality, the fruit
simply provides the electrolyte for charge balance, it is the oxidation and reduction
of various metals that provide the electron flow.
Several factors can change the voltage and amperes of the batteries.
Different metals in set up will produce different voltage due to a difference in
affinity for electrons. Varying the electrolyte will also vary the current, as different
electrolytes provide different levels of resistance. Juice, for example, has less
resistance than fruit, permitting a higher current. Heating the battery can also
increase the current, because of an increase in kinetic activity. Combining multiple
cells can increase the voltage and current produced, allowing for electronics with
higher needs to be run from these batteries. Two different set ups, series and
parallel, result in different voltage and amperes. Setting up multiple batteries in
parallel results in higher voltage, the addition of the voltage of all attached batteries,
but the amperage remains the same. In a series circuit, the voltage remains the
same, but the current (amps) adds up. When a device doesn’t work, it is because
either the voltage or the current is too low. This can be remedied by combining
multiple cells to achieve the voltage and amps need to power the device.
Materials Needed (per group):
Fruits of various kinds (oranges, apples, bananas, limes, lemons, etc.)
Pennies (one for each individual cell)
Galvanized nails (one for each individual cell)
Strips of zinc and copper, or copper wire
Fruit juice (120 ml)
Milk (100 ml)
Soda (100 ml)
Beakers or cups large enough for 140 ml of liquid and metal
Ten Alligator clamp wires
A couple of clamps to hold wires and metal strips
Voltmeter
Miniature LED
Other small electronic devices (optional)
Hot Plate
Safety Information
Caution should be used when utilizing the hot plate, as it can attain
temperatures that can burn. Students should wash their hands after touching the
galvanized (zinc coated) nails.
General Outline of Procedures:
Explain to the students that they are managing a local general store, but have
no power in their establishment due to an ice storm. Without lights or clocks (or
other electronically powered devices), nobody can see to shop, nor can employees
keep track of their hours. Thankfully, being a general store, a number of items can
be utilized to create electricity through energy stored in chemical bonds. A redox
reaction between zinc and copper can provide the electron flow, but an electrolyte is
needed. Describe how ions works and can convey charge. Ask them to test which of
Power Outage at the Grocery Store, CALEB HARRIS, 1/29/14
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the various grocery items utilized as an electrolyte can provide the highest amount
of volts and amps to power the devices? Explain voltage and current now.
Divide the students into groups based on different types of fruits, give each
group multiples of the same fruit and a voltmeter, along with a LED light. Provide
each group with wires and enough pennies and zinc nails so that each individual
fruit can form a battery cell. Demonstrate the set up of a single cell and how to
measure the volts and amps on the voltmeter, followed by a demonstration of how
to hook up the LED. The teacher should go around and make sure that students are
assembling the cells in the correct manner, first they will be doing solid fruit cells
and then cells with liquid electrolyte. Remind students to write down the results of
the tests as well as any observations they might make about the color at the
cathodes and anodes. If a hot plate can be obtained and there is enough time, the
cells can be heated. Students can see that the current increases as the electrolyte is
heated for one of their liquid cells. The teacher should stand by to ensure safety.
After single cells of differing electrolytes have been completed and the LED
has been tested (it should not have worked), the students will move on to combining
multiple liquid electrolyte cells to increase voltage and amperes. The two set ups,
series and parallel, can be confusing. When asked about how to create each
assembly, remember that series connects opposite cathodes and anodes, while
parallel connects cathodes to cathodes and anodes to anodes.
Source: http://van.physics.illinois.edu/qa/listing.php?id=2392
+
Cathode
Red
Anode
Black
Depending on the energy needs of the device, it eventually should work. The
main key to troubleshooting faulty circuits is to make sure that the positive and
negative ends are set up correctly, with LED’s the longer prong should be aligned
with the negative anode and the shorter one with the positive cathode in order for
the LED to light up. After the students have devised how to power the devices off of
Power Outage at the Grocery Store, CALEB HARRIS, 1/29/14
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multiple juice battery cells, students will try other solutions to see if they work with
making a battery. After all of this is done, ask students to deconstruct the batteries
and pour the liquid electrolyte solutions down the sink.
To begin the discussion, ask which of the solid fruits produced the highest
voltage and current. Ask whether the solid fruit or the liquid electrolyte cells had a
higher voltage. Why is this? Find out what other types of liquids were good
electrolytes and could keep the cell running. As a grocery store owner, what is the
final verdict as to what solution they would use to power their necessary small
devices?
Extra Activity
For older students, discuss what an alkaline battery is and how it works,
using zinc and manganese (zinc is reduced, manganese is oxidized). Pull out a copy
of the activity series and discuss reduction potentials and how the table can be used
to predict which circuits will have higher voltage potentials. Also, see if they noticed
a chemical color change at the cathode and anode? Why might this be? Is this a
chemical or physical change? If you can obtain more metals, you can try making
batteries out of these different metals.
If a hot plate can be obtained and there is enough time, the cells can be
heated. Students can see that the current increases as the electrolyte is heated for
one of their liquid cells. The teacher should stand by to ensure safety. Current
should increase, due to a rise in kinetic activity.
Sources
Q&A: Lemons in Series; Lemons in Parallel, University of Illinois Physics. Accessed
online 1/9/14 at:
http://van.physics.illinois.edu/qa/listing.php?id=2392
Alkaline Dry Cells, Georgia State University. Accessed online 1/13/14 at:
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/battery.html#c3
Current vs. Voltage, Diffen. Accessed online 1/13/14 at:
http://www.diffen.com/difference/Current_vs_Voltage
Power Outage at the Grocery Store, CALEB HARRIS, 1/29/14
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Power Outage at the Grocery Store
Student Worksheet
Name:______________________________________
The Situation
Another winter storm has hit your community, and you, a grocery store
owner, have no power to light the store or power the burglar alarms. Thankfully,
having studied chemistry in college, you know of an energy source that may be able
to help power the store.
Metals have electrons that some want to give away and some want to keep
more than others. Electricity is just a current of running electrons, negatively
charged particles, so if we can harness one metal transferring its electrons to the
other, we can have some electricity through reduction and oxidation reactions. The
two metals that we have available in quantity in the store are zinc and copper. Zinc
wants less electrons to become more positive, and copper wants electrons in order
to become more negative. However, in order to balance out the charges, positive
charges must work their way back from the copper to the zinc. Unlike electrons,
positive charges cannot travel along a wire. Rather, they can travel between the
metals through an electrolyte solution, a solution of charged particles. The
electrolyte solution can be anything that conducts electricity. In order for our
battery to work, we will need to find one that allows the most current to flow. We
will measure this using a voltmeter. These can measure both volts and current (in
amperes, or amps).
Testing Electrolytes
The first electrolyte we will be testing will be a piece of solid fruit. The juice
of the fruit will act as the charge conductor. Roll the fruit, squishing it to release the
juice inside. Grab a penny and a galvanized (zinc-coated) nail. Stick them into the
fruit, making sure not to touch them, lest the reaction happen without the electrons
running our circuit. Hook the voltmeter up to the nail and the penny. The nail is the
cathode, the positive terminal from which electrons come from. The penny is the
anode, the negative terminal to which the electrons go. The red clamp of the
voltmeter should go to the anode, and the black to the cathode. Measure the voltage
and then the amps of this cell, recording them below.
Volts
Amps
You may notice some dark metal stains around the electrodes of the fruit
battery. This is just the newly oxidized or reduced metal in contact with the fruit
after losing or gaining electrons. The membranes of the fruit provide resistance to
the flow of electrons, much like friction does when stopping something sliding
downhill. A better fruit electrolyte would not include these membranes. A pure
juice would have the conductive abilities while lowering resistance, the “friction”
on the current that makes it moves slower. Using a 150 ml beaker, clamp down a
Power Outage at the Grocery Store, CALEB HARRIS, 1/29/14
5
zinc strip to the side, and twist a copper wire around the other side, again, making
sure that they don’t touch. Pour 60 ml of orange juice into the beaker. Hook the
voltmeter up to this cell and record the voltage and the amps below.
Volts
Amps
With this decrease in resistance, the amps should rise. The voltage should
remain roughly the same, due to the voltage being determined by the two metals
and the difference in how much the metals want to hang on to electrons.
Another way to raise the current is to increase the volume of the electrolyte
solution. Add another 60 ml of orange juice into the beaker. Measure the voltage
and record.
Volts
Amps
Test the LED. Does it work?
It shouldn’t, as there is not enough voltage to power the LED. In order to
power the LED, more voltage is needed. The LED’s do not require much current, but
need about 1.5 volts to work. We need to set up multiple cells in order to power the
light. If we want more voltage, we will need to set the cells up in series. This allows
us to add the voltages up, with the current remaining the same. To do this, take two
cells. Using the alligator clamp wires, attach the zinc electrode of one cell to the
copper electrode of the other. Look at the figure below for reference, if you need
help. Measure the volts and amps of this cell, recording below.
Number of Cells
2
Volts
Amps
Test the LED and see if it works. If not, try adding another cell. With this
three cell set up, hook a buzzer up and see if you can get it to work.
Number of Cells
3
Volts
Amps
If we wanted constant voltage, but more current, we could set the circuit up
in parallel, meaning we would get the same voltage as we would get from one cell,
but the current adds up instead. Hook up the copper to the copper and the zinc to
the zinc, ending up with one wire from each to attach to the voltmeter or electrical
devices. Record the volts and the amps in the table. Refer to the below diagram if
you need help with either the series or the parallel set up.
Power Outage at the Grocery Store, CALEB HARRIS, 1/29/14
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Source: http://van.physics.illinois.edu/qa/listing.php?id=2392
Number of Cells
Volts
Amps
2
Testing
Now, having seen several examples of how the batteries are set up and some
ways to increase voltage and amps, use the other provided materials to play around
and see what kind of batteries give off the most voltage and amps. Experiment with
different metals and electrolytes in various set-ups. Record what the battery
consisted of, as well as your results and observations below.
Cell of Your Choice:
Number of Cells
Volts
Amps
Does the LED light work? Yes/No
Does the buzzer work? Yes/No
Observations:
Cell of Your Choice:
Number of Cells
Volts
Amps
Does the LED light work? Yes/No
Does the buzzer work? Yes/No
Power Outage at the Grocery Store, CALEB HARRIS, 1/29/14
7
Observations:
Cell of Your Choice:
Number of Cells
Volts
Amps
Does the LED light work? Yes/No
Does the buzzer work? Yes/No
Observations:
Cell of Your Choice:
Number of Cells
Volts
Amps
Does the LED light work? Yes/No
Does the buzzer work? Yes/No
Observations:
Conclusion
Based on several factors, the current and voltage vary. What setup would
you use to get the highest voltage from a single cell? Why is this?
Power Outage at the Grocery Store, CALEB HARRIS, 1/29/14
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In actuality, it would take a whole lot of zinc and copper to make enough
energy to power a real life grocery store. These cells would have to be combined in
order to produce enough power to run anything useful. Do some research. What is
the difference between a standard battery (Energizer, Duracell) and the batteries we
created today?
For older kids, look up the activity series. What other metals would give us
more voltage? Why is this?
Optional Extra Activity
There are other ways to raise the current of a cell. Heat is one of them. Why
do you think this is?
The higher temperature increases the kinetic activity, allowing the current to
be conducted more easily. Take your fruit juice cell up to the front of the classroom
and set it on the hot plate, leaving the voltmeter attached. Measure the amps as the
orange juice heats up. Write the voltage and amps in the table below when the
temperature is 100 degrees Fahrenheit.
Volts
Amps
Power Outage at the Grocery Store, CALEB HARRIS, 1/29/14
9
Power Outage at the Grocery Store
Student Worksheet
Today we will be making batteries out of different materials. Below is a lot of space
to record results and observations about the cells. This is an image of a general set
up for any battery.
Source: http://www.brighthubengineering.com/commercial-electrical-applications/64675-why-does-lemonconducts-electricity/
Trial 1. Fruit Battery with Solid Fruit
Type of Fruit:__________________________
Volts
Amps
Observations:
Trial 2. Orange Juice
Volume
Volts
Amps
Additional Orange Juice Trial
Volume
Volts
Amps
Power Outage at the Grocery Store, CALEB HARRIS, 1/29/14
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Does the LED light work? Yes/No
Observations
Here is a diagram for the series and parallel set ups.
Source: http://van.physics.illinois.edu/qa/listing.php?id=2392
Trial 3. Multiple Cell Series Juice Setup
Number of Cells
2
Volts
Amps
Does the LED light work? Yes/No
Does the Buzzer Work? Yes/No
Additional Series Trial
Number of Cells
Volts
Amps
Does the LED light work? Yes/No
Does the buzzer work? Yes/No
Observations:
Power Outage at the Grocery Store, CALEB HARRIS, 1/29/14
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Trial 4. Multiple Cell Parallel Juice Setup
Number of Cells
2
Volts
Amps
Does the LED light work? Yes/No
Does the buzzer work? Yes/No
Number of Cells
Volts
Amps
Does the LED light work? Yes/No
Does the buzzer work? Yes/No
Observations:
Trial 5. Juice with Heat (Optional)
Temperature
Volts
Amps
Observations:
Cell of Your Choice:
Number of Cells
Volts
Amps
Does the LED light work? Yes/No
Does the buzzer work? Yes/No
Observations:
Power Outage at the Grocery Store, CALEB HARRIS, 1/29/14
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Power Outage at the Grocery Store, CALEB HARRIS, 1/29/14
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