Unit 7 – Energy to Go - Batteries
STUDENTS’ GUIDE
CHALLENGE
How does a battery work? What is your use of batteries and how does this impact
sustainable energy use in Hong Kong?
ACTIVITY FOCUS
Batteries and how they are used are investigated. A WET CELL is constructed to
learn more about batteries. The environmental consequences of battery disposal are
discussed. The tradeoffs involved in the use of regular and RECHARGEABLE
batteries are identified.
MATERIALS
1
1
1
Part B
For each group of students
100ml Beaker
30g Salt (NaCl)
Copper strip
1 Wet cell apparatus
Magnesium strip
1 piece of steel wool
1 Stirrer
SAFETY NOTE
Be sure to use safety goggles during this investigation. HYDROGEN
PEROXIDE can discolour clothing.
PROCEDURE
Part A Reading and Discussion
1. Group Discussion
Discuss with your group and make notes about how all of you and your families use
batteries. Each person in your group should think of and list as many different
batteries that they use and what they use them for.
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2. Reading
A Closer Look at Batteries
Think of a battery as an energy converter. It is able to convert or transform chemical
energy into electrical energy. Look at the accompanying diagram of a battery and
read about the various parts and how they work.
Today’s common flashlight battery is an ALKALINE CELL, also called an electric
cell. A cutaway diagram of one is pictured above. All batteries contain a liquid,
paste, or solid material that electricity can flow through. This material is called an
ELECTROLYTE. The electrolyte in the D-cell alkaline battery pictured is a moist
paste of potassium hydroxide. The cell is sealed to prevent moisture from
evaporating.
Batteries provide electrical energy by using chemical reactions to produce electrons
that can flow in a circuit. The flow of electrons is what we commonly call electricity.
In a battery, a metal is used to provide the source of electrons. In the case of the
alkaline battery, this metal is zinc. Other batteries may use silver, lithium or nickel
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as the source of electrons. When you turn on a flashlight you produce an external
circuit or path for electron flow. A chemical change takes place inside the batteries
that provide energy to the flashlight. When the battery is turned on, a circuit is
completed that allows the zinc atoms to lose electrons. These electrons move from
the negative terminal of the battery and then travel to the positive terminal, through
the bulb to interact with the manganese dioxide paste. The potassium hydroxide
acts as an electrolyte (a material that can conduct electrical charge – like salt water)
allowing the movement of electrons inside the battery. This flow of electrons is the
electrical current, which passes through the flashlight bulb and produces the light.
This chemical change cannot be reversed. The battery dies when the reactants are
used up. This type of battery is called a primary or non-rechargeable cell. Other
types of batteries called secondary cells are rechargeable. The LEAD-ACID
BATTERIES in motorcycles and automobiles are examples of secondary cells.
3. Question
Explain to your partner, in your own words, why a battery “dies”. After you have
both shared with each other, list your ideas in your science notebook.
Part B Building and Investigating a Wet Cell
Introduction
Batteries are objects that contain materials in which chemical changes take place. You
will construct a simple chemical battery or wet cell and explore whether changing the
distance between the metals changes the electrical energy produced. You will use a
small motor and propeller set up to detect and compare how much energy is produced.
Note: It is extremely important to dry the metals on a paper towel and clean both
sides with the steel wool before using them for the next test!
Procedure
1. In your group, add 100 mL water to the beaker and stir in 30g of salt to produce a
saturated solution. Ask your teacher to add 25 drops of hydrogen peroxide.
2. Use the motor and propeller set up provided.
3. Clip the MAGNESIUM strip to one crocodile clip on the motor board and connect
the copper strip, to the other crocodile clip on the motor board. See the picture at
the back of this page for illustration.
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4. Lower the pieces of metal into the container opposite from each other. Observe how
fast the propeller spins. Next, remove the two metal pieces. Record their
appearance in your science notebook. Dry them, and then shine them with a piece
of steel wool.
5. As a group, determine what happens to the energy produced by the battery when
the two metals are placed closer to each other. Place them at opposite ends.
Gradually move the magnesium strip closer to the copper strip. Describe in your
science notebook how the speed of the motor changes as you move the metal strips
closer.
6. Explore what happens to the direction the motor turns when you reverse the
connections on your two metals. What does this tell you about the direction (path)
that electrons are flowing in the circuit?
GOING FURTHER
As time permits, investigate one of the following questions.
1. How does changing the concentration of the salt or hydrogen peroxide affect the
amount of energy produced?
2. What effect does slowly removing one of the metals from the beaker have on how
fast the motor turns?
First, design an investigation and write up the procedure in your science notebook.
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After your teacher approves your design, do the investigation and record your results.
Write a three-paragraph summary of your work using the following guidelines.
o What did you investigate and how did you look for it?
o What did you find out?
o What does this mean?
Part C Sustainable Battery Use in Hong Kong
Introduction
When we find ways to use fewer batteries while maintaining the benefits of using
batteries, we are contributing to sustainable battery use in Hong Kong.
Reading about “CUT-OFF VOLTAGES “
A battery as you know is a chemical reaction in operation. As the battery is used, the
reacting chemicals change or are diluted and the battery loses some of its potential
energy measured by the voltage. When the reactants are used up, or their concentration
falls to a low level, the reaction stops and the battery is considered dead. Many
electronic games and portable cassette players actually have a cut-off voltage; that is,
below a certain voltage, they will not operate the appliance, even though the batteries
may still contain 50% of their original energy. The battery can still be used in other
applications that require lower cut-off voltages and currents. Most of the batteries we
throw away are really not dead!
1. Review the table below in relation to the list of battery uses your group put together.
Discuss effective ways to increase the use of batteries based on the cut off voltages of
the devices they are used in. Be ready to recommend your one or two top choices to
the class.
Cut-off Voltages for Some Common Products
Product
Cut-off point (volts)
Auto focus 35mm Cameras
1.3
Flashlight
1.2
Headphone / CD Player
1.2
Pencil Sharpener
1.2
Headphone / Cassette Player
1.0
AM/FM Digital Radio
1.0
Portable Shaver
1.0
AM/FM Transistor Radio
0.8
Remote Control for TV
0.8
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Single Use vs. Rechargeable Batteries
2. As shown in the table below, use of rechargeable batteries can reduce the number of
single use batteries that end up as wastes.
Table 6 – Alkaline or Rechargeable Batteries (NMH)
Battery Type
Cost per
Hours each No. needed for Total cost *
(All 1.5-Volt D Cells) battery
battery lasts 500 hours use
Alkaline
Rechargeable
*Includes charger unit and cost of electricity to recharge
3. What are the advantages and disadvantages or TRADEOFFS involved in using
rechargeable instead of single use batteries? Make a list of your ideas in your
science notebook. In your group, discuss these ideas and be prepared to report to
the class on your discussions.
4. What other ways can you reduce the number of dead batteries that end up as
household wastes in Hong Kong? List in your science notebook the three most
important ways you can help reduce the number of dead batteries disposed as
household wastes in Hong Kong.
Personal Reflection
In your science notebook answer the following two questions:
1. What new ideas do I have now about batteries and their use?
2. How can I apply them in my life?
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