This experiment shows how a battery works using electrochemistry. The copper electrons are chemically reacting with the lemon juice, which is a weak acid, to form copper ions (cathode, or positive electrode) and bubbles of hydrogen.
These copper ions interact with the zinc electrode (negative electrode, or anode) to form zinc ions. The difference in electrical charge (potential) on these two plates causes a voltage.
Materials:
- one zinc and copper strip
- two alligator wires
- digital multimeter
- one fresh large lemon or other fruit
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Download Student Worksheet & Exercises
Roll and squish the lemon around in your hand so you break up the membranes inside, without breaking the skin or leaking any juice. If you’re using non-membrane foods, such as an apple or potato, you are all ready to go.
Insert the copper and zinc strips into the lemon, making sure they do not contact each other inside. Clip one test wire to each metal strip using alligator wires to connect to the digital multimeter. Read and record your results.
What happens when you gently squeeze the lemon? Does the voltage vary over time?
You can try potatoes, apples, or any other fruit or vegetable containing acid or other electrolytes. You can use a galvanized nail and a copper penny (preferably minted before 1982) for additional electrodes.
If you want to light a light bulb, try using a low-voltage LED in the 1.7V or lower hooked up to several lemons connected in series. For comparison, you’ll need about 557 lemons to light a standard flashlight bulb.
What’s going on?
The basic idea of electrochemistry is that charged atoms (ions) can be electrically directed from one place to the other. If we have a glass of water and dump in a handful of salt, the NaCl (salt) molecule dissociates into the ions Na+ and Cl-.
When we plunk in one positive electrode and one negative electrode and crank up the power, we find that opposites attract: Na+ zooms over to the negative electrode and Cl- zips over to the positive. The ions are attracted (directed) to the opposite electrode and there is current in the solution.
Electrochemistry studies chemical reactions that generate a voltage and vice versa (when a voltage drives a chemical reaction), called oxidation and reduction (redox) reactions. When electrons are transferred between molecules, it’s a redox process.
Fruit batteries use electrolytes (solution containing free ions, like salt water or lemon juice) to generate a voltage. Think of electrolytes as a material that dissolves in water to make a solution that conducts electricity. Fruit batteries also need electrodes made of conductive material, like metal. Metals are conductors not because electricity passes through them, but because they contain electrons that can move. Think of the metal wire like a hose full of water. The water can move through the hose. An insulator would be like a hose full of cement – no charge can move through it.
You need two different metals in this experiment that are close, but not touching inside the solution. If the two metals are the same, the chemical reaction doesn’t start and no ions flow and no voltage is generated – nothing happens.
Exercises
- What kinds of fruit make the best batteries?
- What happens if you put one electrode in one fruit and one electrode in another?
- What happens if you stick multiple electrode pairs around a piece of fruit, and connect them in series (zinc to copper to zinc to copper to zinc…etc.) and measure the voltage at the start and end electrodes?
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Sure, you can use an orange.
Can I use an orange instead of a lemon or lime?
You can try one large paperclip, but be sure that the other electrode is copper.
you said we could use two large paper clips electrically connected together. Can we use one large paper clip that is straightened?
I have Brian’s electronics kit!!!
I love the Experiment!!
The fruits and vegetables don’t have any electricity on their own. But when you insert the copper and zinc strips, the resulting chemical reaction creates an abundance of electrons on one of the strips. That abundance of electrons causes electricity to flow…which can be measured in volts.
does the fruit or vegetable have electricity? ..if it has volts?
Most LEDs require about 2 volts in order to glow. You may need to put more than one “fruit battery” in series in order to reach that voltage.
We got our battery to register on the multimeter, and then we tried connecting it to an LED we had from the electricity unit, but it didn’t light up. Is there not enough voltage to light up an LED?
You definitely want the setting for DC (straight line and dotted line). You’ll want to use the lowest voltage range on your multimeter. We wouldn’t expect to see more than a couple volts. The fact that you see a measurement when your meter is set to 9V tells me that you most likely had a bad connection. Try redoing your connections and then measure again using the lowest voltage setting.
I am having problems. I have a digital multimeter that has 2 settings on the multimeter. V with a wavy line above and a V with a straight and dotted line. One stands for AV and the DC. Neither read any of the vegetables or fruit but when I changed the setting to the 9V setting it started reading it. Am I doing this cprrectly? Thanks
I’ll have my team connect with you right away!
I don’t understand how I do not have access to experiments. I thought if I got the membership, I would have access to the experiments. I would like access to this experiment, please.
hi
oooooooooh thats cool!
Try Radio Shack – they sell them online and ship them to your door.
Cool! I never knew that you could use fresh produce as a battery! I can’t find alligator clips at The Home Depot though, and it will be about a week till we need another trip to Walmart. Do you know if you can get alligator clips at Target though?
Try it and see! (I’ll give you a hint – you need something that has acid inside.)
SUPER COOL !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! = ) – Isabel Pitcher, 8 yrs.
Can you use leafy veggies such as cabbage, kale, collard greens, swiss chard etc.??? ~ Jasmin Pitcher, 11 yrs.
The video keeps getting stuck on the same spot.
You can hook up the copper of one lemon to the zinc plate of another, so you’re in effect hooking it up in series (plus to minus). You can use paperclips, although the surface area isn’t a large as a strip. This experiments works better if you use a separate lemon for each set of electrodes when connecting them up together.
How do we hook up more than one to get more power? We aren’t going to buy a digital multimeter. We tried a single christmas light bulb which lights up with a AA battery 1.5 V. How do you hook up more than one fruit or potato? We have copper and zinc sticks from the chemistry set. They can pierce through a few at a time since they are long, but that didn’t work. Do we need separate strips and clips for each fruit?
The easiest places to get zinc and copper are by using a galvanized nail and a copper penny. If you really want the strips, you can order them online: zinc and copper electrodes, or a full set.
Where can I buy: one zinc and copper strip? Thanks.