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The lemon battery is an experiment proposed as a project in many science textbooks around the world. . It consists of inserting two different metallic objects, for example a galvanized nail and a copper coin, into a lemon. These two objects work as electrodes, causing an electrochemical reaction which generates a small potential difference. The zinc works as the negative terminal while the copper is its positive terminal.
A lemon cell battery is made with a lemon and two metallic electrodes of different metals. In practice, a single lemon cell is incapable of lighting a light bulb.
The aim of this experiment is to show students how batteries work. After the battery is assembled, a multimeter can be used to check the generated voltage. In order for a more visible effect to be produced, two or more cells connected in series can be used to power a standard LED. Flashlights are generally not used because the battery is not able to produce the amount of current that is necessary to light one of them.
In a lemon battery, both oxidation and reduction occur. At the anode, zinc is oxidised:
- Zn → Zn2+ + 2 e-
At the cathode, hydrogen is reduced:
- 2H++ 2e- → H2
There is an energy change:-
Light and heat energy
Potatoes , apples, or any other fruit or vegetable containing acid or other electrolyte can be used, but lemons are preferred because of their higher acidity  . Other metal combinations (such as magnesium-copper) are more efficient: for example, using a magnesium strip instead of zinc increases the voltage from .97 V with zinc to 1.6 V with magnesium (the exact voltage varies depending on the lemons.) However, zinc and copper are usually preferred because they are reasonably safe and easy to obtain.
It should be noted that the energy used to power this circuit ultimately comes from the energy used in the electrode factories to reduce metallic ions forming the solid metallic electrodes. The lemon simply provides a salt bridge for the reaction to occur.
This experiment may leave the lemon's juice poisonous because of dissolved copper salts.
- Daniell cell
- Battery (electricity)
Categories: Electric batteries | Battery shapes | Disposable batteries | Biotechnology