The lemon battery experiment is a classic science project that illustrates an electrical circuit, electrolytes, the electrochemical series of metals, and oxidation-reduction (redox) reactions. The battery produces enough electricity to power an LED or other small device, but not enough to cause harm, even if you touch both electrodes. Here is how to construct a lemon battery, a look at how it works, and ways of turning the project into an experiment.
Lemon Battery Materials
You need a few basic materials for a lemon battery, which are available at a grocery store and hardware store.
- Galvanized nail
- Copper penny, strip, or wire
- Wires or strips of aluminum foil
- Alligator clips or electrical tape
- An LED bulb, multimeter, digital clock, or calculator
If you don’t have a lemon, use any citrus fruit. A galvanized nail is a steel nail that is plated with zinc. The classic project uses copper and zinc because these two metals are inexpensive and readily available. However, you can use any two conductive metals, as long as they are different from each other.
Make a Lemon Battery
- Gently squeeze the lemon or roll it on a table to soften it. This helps the juice flow within the fruit.
- Insert the copper and zinc into the fruit. You want the maximum surface area in the juicy part of the fruit. The lemon peel helps support the metal, but if it is very thick and the metal does not reach the juice, scrape away part of the peel. Ideally, separate the metal pieces by about 2 inches (5 centimeters). Make sure the metals are not touching each other.
- Connect a wire to the galvanized nail using an alligator clip or electrical tape. Repeat the process with the copper item.
- Connect the free ends of the wire to an LED or other small electronic device. When you connect the second wire, the light turns on.
Increase the Power
The voltage of a lemon battery is around 1.3 V to 1.5 V, but it generates very little current. There are two easy ways of increasing the battery’s power.
- Use two pennies and two copper pieces in the lemon. You don’t want any of the metal pieces within the fruit to touch. As before, connect one zinc and one copper piece to the LED. But, wire the other zinc and copper to each other.
- Wire more lemons in series with each other. Insert a nail and copper piece into each nail. Connect the copper of one lemon to the zinc of the next lemon. Connect the nail at the end of the series to the LED and the copper at the end of the series to the LED. If you don’t have lots of lemons, you can cut up one lemon into pieces.
How a Lemon Battery Works
A lemon battery is similar to Volta’s first battery, except he used salt water instead of lemon juice. The zinc and copper are electrodes. The lemon juice is an electrolyte. Lemon juice contains citric acid. While both salts and acids are examples of electrolytes, acids typically do a better job in batteries.
Connecting the zinc and copper electrodes using a wire (even with an LED or multimeter between them) completes an electrical circuit. The circuit is a loop through the zinc, the wire, the copper, and the electrolyte, back to the zinc.
Zinc dissolves in lemon juice, leaving zinc ions (Zn2+) in the juice, while the two electrons per atom move through the wire toward the copper. The following chemical reaction represents this oxidation reaction:
Zn → Zn2+ + 2e−
Citric acid is a weak acid, but it partially dissociates and leaves some positively charged hydrogen ions (H+) in the juice. The copper electrode does not dissolve. The excess electrons at the copper electrode combine with the hydrogen ions and form hydrogen gas at the copper electrode. This is a reduction reaction.
2H++ 2e− → H2
If you perform the project using lemon juice instead of a lemon, you may observe tiny hydrogen gas bubbles forming on the copper electrode.
Try Other Fruits and Vegetables
The key for using produce in a battery is choosing a fruit of vegetable high in acid (with a low pH). Citrus fruits (lemon, orange, lime, grapefruit) contain citric acid. You don’t need a whole fruit. Orange juice and lemonade work fine. Potatoes work well because they contain phosphoric acid. Boiling potatoes before using them increases their effectiveness. Sauerkraut contains lactic acid. Vinegar works because it contains acetic acid.
- Experiment with other materials for the electrodes besides a galvanized nail and copper item. Other common metals available in everyday life include iron, steel, aluminum, tin, and silver. Try using a nickel and a penny. What do you think will happen if you use two galvanized nails and no copper, or two pennies and no nails? What happens if you try to use plastic, wood, or glass as an electrode? Can you explain your results?
- If you have a multimeter, explore whether the distance between the electrodes affects the voltage and current of your circuit.
- How big is the effect of adding a second lemon to the circuit? Does it change the voltage? Does it change the current?
- Try making batteries using other foods from the kitchen. Predict which ones you think will work and test them. Of course, try fruits and vegetables. Also consider liquids like water, salt water, milk and juice, and condiments, like ketchup, mustard, and salsa.
The lemon battery dates back to at least 2000 years ago. Archaeologists discovered a battery in Iraq using a clay pot, lemon juice, copper, iron, and tar. Of course, people using this battery did not know about electrochemistry or even what electricity was. The use of the ancient battery is unknown.
Credit for discovery of the battery goes to Italian scientists Luigi Galvani and Alessandro Volta. In 1780, Luigi Galvani demonstrated copper, zinc, and frog legs (acting as an electrolyte) produced electricity. Galvani published his work in 1790. An electrochemical cell is called a galvanic cell in his honor.
Alessandro Volta proved electricity did not require an animal. He used brine-soaked paper as an electrolyte and invented the voltaic pile in 1799. A voltaic pile is a stack of galvanic cells, with each cell consisting of a metal disk, an electrolyte layer, and a disk of a different metal.
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