Why Is Milk White?: & 200 Other Curious Chemistry Questions (2013)
8. Chemistry in the World
How do you use chemistry to make a battery?
Metals are used to make a battery. Metals have a convenient property called conduction, in which the electrons in the metal are not bound to just one atom at a time as in other materials but are free to wander from atom to atom. This allows the metals to conduct electricity, because electricity is just charged particles moving through something like a wire.
Many other things can also conduct electricity. For example, hydrochloric acid is a good conductor. When hydrogen chloride (HCl) dissolves in water, it breaks up into hydrogen ions (H+) and chloride ions (Cl-). These electrically charged particles can move through the water. Moving charged particles is electricity.
If you put a strip of aluminum and a strip of copper into the same acid and then the two metal strips are connected to a meter, you can watch electricity being created. Copper holds on to electrons more tightly than aluminum does. Electrons start to move from the aluminum, through the meter, to the copper.
This leaves the aluminum with a positive charge. It attracts the negative chloride ions to it, through the water. The chloride ions attract positive aluminum ions away from the metal strip and into the water, where they form an aluminum chloride solution.
At the copper strip, the extra electrons attract the hydrogen ions in the solution to migrate toward the copper. When they get there, they can steal the electrons to become hydrogen gas. The hydrogen gas bubbles up out of the solution. This keeps up until there is no more aluminum left on the aluminum strip. All the electrons flowing from the aluminum to the copper have been moving the needle of the meter, showing us that electricity has been produced.