Question: We make those batteries at school out of oranges, how do they work?

Sam Geen answered on 24 Jun 2013:

Oranges are full of citric acid. The acid is what gives the battery energy. When you put a wire with a zinc probe on one end and a copper probe on the other end:
– The zinc gets dissolved into the orange as a zinc ion and loses 2 electrons, which flow up the wire.
– At the copper end, the electrons from the zinc end get given to the hydrogen ions (basically protons) floating around in the acid, which makes H2, or hydrogen gas. Note that an acid always has hydrogen ions floating around in it, which is what makes it acidic.
– The electrons flowing from the zinc end to the copper end is what makes the electricity in the wire, which you can use to power a clock, light a small bulb, etc.