Draft 4 - 8/18/05
Mike Boll & Alan Muirhead
We use stored electrical energy every day in the form of electrochemical cells or batteries. The batteries that start our cars and the ones that power remote controls, cell phones, and watches are all examples of electrochemical cells. In this experiment we will build a simple battery to help us find out how batteries work.
For this experiment you will need:
Begin by rolling the orange on a flat surface, while pressing on it with the palm of your hand until the orange feels squishy. This will release the juices in the orange, helping the reaction occur. Next, wrap one of the lengths of wire around the nail, and insert the nail into the orange. Press down on the nail until it is fully inserted into the orange. Next, wrap the other piece of copper wire around the penny a few times and insert it into the orange, making sure the penny does not touch the nail inside the orange.
You now have a working battery. How can you test your battery to make sure it is working?
Make sure the wires do not come in contact with each other, as this will cause a short circuit, allowing electricity to flow back into your fruit before you can use it. To test your battery you can connect the two ends of the wires to the leads on an LED or to your LCD clock. If you are using an LED, simply connect the wire from the penny to one of the wires coming out of the LED by wrapping the copper wire around the wire from the LED, or by pinching them together with your fingers. Then connect the wire from the nail to the other wire on the LED. If nothing happens, don't worry. LED is short for Light Emitting Diode. You probably know that LEDs give off light, which explains the light emitting part. What is a diode?
A diode is an electrical device that allows current to flow in only one direction. So if your LED does not light up, try switching the wires, so that the current from your battery flows through the LED in the other direction. Does your LED light up now?
If you are using an LCD clock, you will need to connect your battery in place of the AA or AAA batteries that normally run the clock. There are metal pieces on either end of the battery housing on your clock. Attach a wire to each of these metal pieces. This may be tricky. You can usually wedge the wire in between the metal terminal and the plastic housing. Whatever method you use is fine as long as you don't destroy the clock, and the connections don't disconnect too easily. You will need to connect the wires in such a way that the wire where electrons are being produced is connected to the negative terminal of the clock or LED. In our experiment, the electrons are being produced at the nail. Let's figure out why.
All electrochemical cells involve two separate reactions; a reaction in which one substance loses electrons (oxidation), and a reaction in which another substance gains electrons (reduction). In a battery, the two reactions occur simultaneously (at the same time), with the oxidation reaction providing the electrons to fuel the reduction reaction.
The zinc coating on the nail (which is what makes the nail "galvanized") is undergoing an oxidation (loss of electrons) and forming zinc ions. The electrons that the zinc metal loses eventually make their way to the copper penny when you complete the circuit by hooking the wires to the LED or clock. At the penny they react with H+ ions (from the citric acid in the fruit) in a reduction reaction forming hydrogen gas. When you hook up the battery to a device like an LCD clock, you need to be sure that you are hooking up the electrode that produces electrons - in our case the zinc-coated nail - to the negative terminal of the clock. This ensures that electrons are always flowing in the proper direction.
If your battery cannot power a clock or LED, don't worry. A single fruit battery usually only produces a voltage of between 0.8 V and 0.9 V. You might want to try hooking up several fruit batteries in series, to get a higher voltage. Make another battery using the same procedure above, and connect the wire from the nail of the second battery directly to the copper penny/wire from the first battery you made. Connecting the batteries in series will produce a voltage that is the sum of the individual voltages of each fruit battery. This is how batteries work in the real world as well. A 12 V car battery is actually made up of 6 individual voltaic cells connected in series. Now that you have a battery with a higher voltage (about 1.6 V to 1.8 V), try hooking up your LCD clock or LED. Does it work now? If your clock still doesn't work, try connecting three batteries in series.
** Yellow LEDs require a higher voltage than red LEDs. If you are using a yellow
LED, you may need to connect several batteries in series to get a large enough
voltage to light up your LED
This experiment has been adapted from information at several sources:
http://www.seps.org/oracle/oracle.archive/Physical_Science.Chemistry/2003.05/001051624574.360.html
http://www.seed.slb.com/en/scictr/lab/fruit/