Food Batteries

Overview:
Create a battery from common foodstuffs, sufficient to light a small lightbulb or LED display.

Equipment:

1. One large potato or lemon.
2. Zinc electrode - a 3cm x 0.5cm piece of zinc metal will suffice. You can inquire at a local hardware store.
3. Copper electrode - Similarly sized piece of copper metal.
4. Copper wire - Sufficient length of wire to create a circuit from the zinc electrode to a lightbulb (or other device) and copper electrode.
5. Small lightbulb - flashlight or penlight bulbs work best. You can experiment with other devices such as LED displays, or time pieces.

Safety:
If no copper electrode is used, hydrogen gas is given off as a byproduct of the reactions taking place. Be wary of performing the experiment near heat sources or an open flame.

Though the voltages and amperages given off are low, care should be taken in handling the wire and other parts of the circuit.

How to do the experiment:

1. Stick your zinc electrode all the way into the potato or lemon.
2. Place the copper electrode on the opposite side.
3. Connect the small lightbulb to the two electrodes with copper wire.
4. Observe what happens!

Explanation: From the MadSci Archives..

Subject: Re: Electricity in produce
Date: Fri Mar 13 10:38:22 1998
Posted By: Dan Berger, Faculty Chemistry/Science, Bluffton College
Area of science: Botany
ID: 886437348.Bt

> Can you please tell me how to measure electricity in Fruits and Vegetables.

The way to measure electricity in anything is with a multimeter, but I suspect that you've tried that and have gotten no results.

The reason for this is that there is no electricity in any fruit or vegetable (in the sense that they are like little batteries). Perhaps you are confused by the fact that you can use the chemical properties of certain fruits and vegetables to generate electricity.

A lemon, for example, can be made to power a small electrical device because the lemon is quite acidic (for a food). The way you do this is to stick a piece of zinc metal and a piece of copper metal (a zinc electrode and a copper electrode) into the lemon. You can then draw electrical power from the lemon through an external circuit and do work. (I am told that a lemon cell is about equivalent to a single calculator battery.)

Here's the chemistry behind the lemon cell: zinc is an active metal and will react readily with acid; acid's active ingredient is positively-charged hydrogen. So a transfer of electrons takes place between the zinc and the acid; the zinc (Zn⁰) is oxidized to Zn⁺⁺ and the acid (H⁺) is reduced to hydrogen gas (H₂), which you can see bubbling out around the electrodes.

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

Useful References:
Try searching the MadSci Archives for potato battery

Further comments:
Try the effect with different fruits and vegetables. How well do other citrus fruits or tomatos work? If using potatoes, how does the size of the fruit or vegetable relate to how long the bulb stays lit? Does the pH of the vegetable relate to the amount of electricity generated? Lastly, what is the maximum Watt lightbulb you can light from your food battery? Try using some electricity equations to calculate parameters such as resistance, voltage and current.