Virtual Library ID: 2108

Grade 6

Strand: Energy and Control, Science

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“Freggie” Batteries

LESSON PLAN DETAILS

Lesson Title: Fruit Juice – making a fruit/vegetable (freggie) battery

Lesson Plan Description: The student will investigate the transformation of chemical to electrical energy through the construction of and experimentation with fruit and vegetable batteries and will apply concepts relating to electrochemistry by constructing a fruit-powered battery. 

The exercise is designed to develop concepts and vocabulary regarding electricity and chemistry (e.g., electrodes, electrolytes, voltage, batteries, etc.).

Objectives:  Students will:

·        construct a battery powered using a potato or citrus fruit;

·        observe and measure electrical voltage;

·        compare voltage production with different types of fruits and vegetables;

·        analyze and discuss observations and data with other students;

·        relate findings to principles of electrochemistry;

·        research common battery types, electrode and electrolyte composition

 

Expectations: (Ontario Curriculum Grades 1-8, Science and Technology, p64

Overall: “…demonstrate understanding that electrical energy can be transformed into other forms of energy;”

Specific: “… identify, through experimentation, ways in which chemical energy can be transformed into electrical energy…;”

Duration: One class period (75 mins.)

 

Materials:

·        potatoes, lemons, limes, and other acidic fruits and vegetables

·        electrical leads with crocodile clip

·        voltmeter

·        pH meter, pH indicator solution or strips

·        resistors – 10kΩ

·        zinc-plated (galvanized) nails, copper nails, short lengths of copper and aluminium piping, small tin-plated can;

·        steel wool to shine the surfaces of the metals

·        low voltage LEDs (various colours)

·        knife

·        kitchen paper

·        pencils, graph paper and lab note books

·        in-class quiz sheets

 

Lesson Extension and Enrichment:

If students finish the experiments early have them

a)     create electrical circuits with additional “freggie” batteries. Describe what is happening and why. 

 

Lesson Plan

Present the course materials that cover the conversion of chemical to electrical energy.  Have a few different types of batteries on hand to ensure that students understand the context and concepts.

Safety:
A small amount of hydrogen gas is given off as a byproduct of the reactions taking place. Don’t perform the experiment near heat sources or an open flame.

Experiment Steps:

Step 1: Making the battery

  1. Clean the inside of the copper pipe with the wire wool;
  2. Cut the potato or lemon into ˝” slides. (If you are using a lemon, roll it on the bench a couple of times to get the juices flowing);
  3. Press the sharp end of the copper pipe into the potato and lemon to create a plug of electrolyte.  Continue to plug the copper pipe until it is nearly full;
  4. Measure and record the pH of the electrolyte used;
  5. Clean the zinc nail (electrode) with the wire wool (The electricity comes from chemical reactions occurring on the surface of the metal in contact with the fruit or vegetable and dirt will interfere with the reactions);
  6. Press the nail through the centre of the filled copper pipe. Don’t let it touch the copper pipe;

Step 2: Making the circuit

  1. Use a lead with crocodile clips to connect the zinc electrode to one side of a 10kΩ resistor. 
  2. Use another lead to connect the copper pipe to the other side of the resistor;
  3. Connect the two leads of the multimeter either side of the resistor;

  1. Observe what happens and record the voltage;
  2. Keeping the electrodes the same, try creating other batteries with different fruits and vegetables as electrolytes;
  3. In lab books, record the experiment, create a drawing of the battery and circuit set-up and tabulate results on the graph paper.
  4. Create batteries using different metal containers and centre electrodes

Step 3: Observations - for each battery type constructed:

  1. Record the electrode metals and electrolyte used.
  2. Try using some electricity equations to calculate current and power output of each battery type.  Tabulate and/or plot your results.
  3. Measure the pH of each battery electrolyte. Take several measurements from different places and average results.  Plot your results.

Lesson Plan (cont.)

Step4: Guide the class in a series of discussions to discover what was learned and the observed results.  Lead the students to identify what they learned regarding the effects of acidity (pH) on the battery voltage.

Step 5: (Time permitting). Students should estimate how many batteries it will take to light LED.  Why?

Student groups work together to create circuits with multiple batteries aiming to light an LED.  Draw the circuit and measure voltages around it. Describe what is happening and why. 

In-Class Quiz:

Assessment:

With the aid of in-class experiment, lab book write-up, quiz and a homework assignment, the assessment of the student will me made along the following lines:

·        Knowledge / Understanding – demonstrate though answers to assessment quiz and the graphing of results and the use of correct terminology.

·        Inquiry – application, problem solving through group activity with the experiment and solo research for the homework assignment.

·        Communication – demonstration of concepts through discussion of the experiment, observed and plotted results, answers to quiz and completion of homework.

Rubrics:

(Source: “Ontario Curriculum Unit Planner”, 3.0 PLNR2002 Official Version)

In-class Questions and Discussion Points:

Q: Does the pH of the vegetable relate to the amount of electricity generated?

Q. Does the voltage of the battery stay the same over time?  If not, why?

Q. Describe using electrical terms (voltage, current, resistance) what is happening in the circuit and come up with ideas as to what and why.

Q. Could this source of power be of commercial value.  State your position and reasoning.

Example Plots of Results

Homework Assignment

Research different types of batteries that use different chemicals and chemical reactions. Provide the name of the type of the battery and name the materials use to make the electrodes and electrolyte.

Teacher Resources

Fruit  / Veggie (Freggie)  Battery – The Chemistry Explained

The fruit / veggie battery is called a voltaic battery, which changes chemical energy into electrical energy.

A battery requires two different electrodes.  The electrodes are usually metals as metals are excellent conductors of electricity. Chemical reactions occur at each electrode.  Oxidation must occur at one electrode (the anode) and reduction at the other (the cathode).  Oxidation and reduction are chemical reactions. 

A battery also requires an electrolyte that conducts electricity and completes the circuit between the two electrodes.  Pure water is a poor conductor of electricity; it is an insulator.  However, a solution of acid or salt in water is a good conductor of electricity.  This is because acids and salts dissolve in water to form ions.  The ions are electrically charged, and can carry a current.  Fruits and vegetables contain water, acids, and salts and can conduct electricity between the two metal electrodes. An orange, lemon, banana, potato, and many other fruits and vegetables can provide the electrolyte for a battery.

In our case we have used zinc for one of the electrodes. Zinc is an active metal that will react readily with the acid.  An acid's active ingredient is positively-charged hydrogen. So a transfer of electrons takes place between the zinc and the acid. The zinc (Zn) is oxidized (gives up electrons) to Zn++ and the acid (H+) is reduced (acquires electrons) to hydrogen gas (H2), which you can see bubbling out around the electrodes. 

               Oxidation:           Zn ŕ Zn++ + 2e-    (Zinc looses 2 electrons.)
               Reduction:          2H+ + 2e- ŕ H2     (Hydrogen ions gain electrons.)
               Net Reaction:     Zn + 2H+ ŕ Zn++ + H2

 

The copper electrode draw powers from the “freggie” cell.  The copper helps channel the electrons through the external circuit – in our case, the 1kΩ resistor.  This sort of cell will work for any fruit or vegetable with some acid content - lemons are good because they're more acidic than most foods.

 

The voltage of the battery is directly proportional to the free energy of the net chemical reaction.  If you know the standard reduction potentials for different metals you can predict the voltage of the battery. The voltage is the difference between the reduction potentials of the two electrodes.  The potentials of reduction of copper and zinc are + 0.342 V and - 0.762 V respectively so the voltage generated is = +0.342 - (-0.762) = +1.104 V.

Battery Types

Some of the more common types of batteries are:

  • Alkaline battery -- Used in Duracell¨ and Energizer¨ and other alkaline batteries. The electrodes are zinc and manganese-oxide. The electrolyte is an alkaline paste.
  • Lead-acid battery -- These are used in automobiles. The electrodes are made of lead and lead-oxide with a strong acid as the electrolyte.
  • Lithium battery -- These batteries are used in cameras for the flash bulb. They are made with lithium, lithium-iodide and lead-iodide. They can supply surges of electricity for the flash.
  • Lithium-ion battery -- These batteries are found in laptop computers, cell phones and other high-use portable equipment.
  • Nickel-cadmium or NiCad battery -- The electrodes are nickel-hydroxide and cadmium. The electrolyte is potassium-hydroxide.
  • Zinc-carbon battery or standard carbon battery -- Zinc and carbon are used in all regular or standard AA, C and D dry-cell batteries. The electrodes are made of zinc and carbon, with a paste of acidic materials between them serving as the electrolyte.

Source: http://www.energyquest.ca.gov/story/chapter05.html

Internet Resources:

1.       http://www.madsci.org/experiments/archive/889917606.Ch.html

2.       http://www.seed.slb.com/en/scictr/lab/fruit/supersize.htm

3.       http://www.energyquest.ca.gov/story/chapter05.html

4.       http://www.ieee-virtual-museum.org/collection/tech.php?taid=&id=2345793&lid=1