Today we’re discussing what may be the most cliché and well known science experiment of all time. Though it 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 around a bit, to break up all of the little juice packets inside, to get it nice and juicy. Stick a nail in one side—it has to be a galvanized nail, meaning it’s coated in zinc. And 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 metre to the copper and zinc, it will show some electric current. But if I asked you why there are electrons flowing 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 electro negativity. That electrode, the one that wants the electrons more is called the cathode, and the one that gives up electrons is called the anode.
In 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 electro negative and thus, our cathode. But if that’s the case, then 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 and 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 an 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 oxidises, or removes electrons from the zinc, and the resulting positively charged zinc ions move in the 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-negativity between zinc and copper.
The electrons would rather be in the copper, and the lemon juice opens the door for them to get there. Want some proof? Well, oftentimes you’ll see lemon battery experiments using 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 zink, not in the lemon.