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Hank shows us another SciShow: Experiment! This time he's tackling what may be the most cliche, well-known and misunderstood experiment of all time: the lemon battery. The take home message in this one is: the electricity is NOT in the lemon. Just that delicious juice.

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References for this episode:
http://hilaroad.com/camp/projects/lemon/lemon_battery.html
http://en.wikipedia.org/wiki/Lemon_battery
{intro}

    Hello and welcome to SciShow experiments.  Today, we're discussing what may be the most cliche and well-known science experiment of all time [the lemon battery experiment], though what is also one of the most misunderstood science experiments of all time.  The important thing to note here: the electricity is not in the lemon.  First, let's do this thing.
    Now roll the lemon a little bit to break up all the little juice packets inside, get it nice and juicy.  Stick a nail in one side, it has to be a galvanized nail, meaning it's coated in zinc.  On the other side, stick something copper, I'm using copper wire.
    You'll probably be unsurprised to discover that when I connect this volt meter to the copper and zinc, it will show some electric current.  But if I asked you why there are electrons lowing from one metal to the other, there's a fairly good chance that you would either be stumped, or you would be wrong. So let's fix that.
    Electric chemical cells, also called batteries, require three things.  Two electrodes and one electrolyte.  One of the electrodes has to have a stronger desire for electrons than the other.  In chemistry, we say that it has a higher electronegativity.  That electrode, the one that wants the electrons more is called the cathode, and the one that gives up electrons is called the anode.
    I our lemon battery here we have copper in the wire and zinc from this galvanized nail.  Copper likes having electrons more than zinc, so it's more electronegative and thus, our cathode.  But if that's the case, why can't we just hook the copper to the zinc, and watch the electrons zoom across?  And what's the point of the lemon?  I bought a lemon and I want to use it!
    Well electrons aren't just gonna abandon their nice stable home and make the metal all positively charged on one side ad negative on the other.  There are a ton of forces that prevent that from happening.  Since zinc is losing all those electrons it's gonna have to lose protons too, and that's where the third component comes in, the electrolyte. The wire that connects the copper and the zinc allows electrons to flow freely but protons are huge compared to electrons and they can't move through wires, that's not a thing that happens, but they can move into a ionic solution. An ionic solution like a dilution of citric acid. And that is our electrolyte. When zinc is exposed to the acid in the lemon juice, the acid oxidizes or removes the electrons from the zinc, and the resulting positively charged zinc ions move into solution. The resulting electrons, they collect in the metal and then rush across the wire into the copper which, if you remember, wants electrons more than zinc does. Those electrons, now in the copper, pull a couple of protons, or hydrogen ions, out of the acid and reduce them, adding electrons. The result is hydrogen gas, which, if we were in there, we might be able to see is very very tiny bubbles forming on the copper electrode. In summary, the electricity is coming, not from the lemon, but from a chemical reaction resulting from the differences in electro negativities between zinc and copper. The electrons would rather be in the copper, and the lemon juice opens a door for them to get there. Want some proof? Well, oftentimes you'll see lemon battery experiments conducted with multiple lemons, connected in series to give you more power. But you don't actually need to do that. If I push in three nails and three copper wires in the same lemon, I get roughly three times as much electric current. As long as there's enough space in the lemon and enough lemon juice, the power is in the zinc, not in the lemon.
Thank you for watching this SciShow Experiment. If you have any questions or ideas or comments we're on Facebook and twitter, and of course down in the comments below, and if you want to keep getting smarter with us you can go to youtube.com/scishow and subscribe.