Green Science calculator with cans

The batteries in your calculator have run out!
Calmly! Empty beverage cans and two pencils will produce enough energy to make the calculator work. Fill both cans with salt water (40 grams of salt per 400 ml of water) to about 2/3 of the height. Put the pencils in both cans. Make sure the pencil tips are in the water. Connect the red wire from the calculator to the screw on the right pencil. Do this by wrapping the exposed part of the cord on the screw. You will create a positive battery pole by connecting the black wire from the calculator to the screw on the can holder on the left side to create a negative battery pole.

How it's working?
The calculator works because the metals in the tin and salt water interact with each other. This interaction is called a chemical reaction. The reaction causes an electrical current in the wires that power the calculator. There are several reactions in the batteries, but the two most important are the reactions on the inner surface of the can and the ends of the pencils.
Small molecules of water, called molecules, are divided into molecules called ions. Some of these ions are hydroxide ions. On the inside of the can wall, aluminum is combined with hydroxide ions to form a substance called aluminum hydroxide. This releases other microparticles, called electrons, which in turn causes the generation of electricity. At the ends of the pencils in salty water, oxygen dissolved in water combines with water and graphite electrons to form hydroxide ions. Each can becomes a cell producing electricity and these two cells merge into a battery that produces enough energy to power the calculator. Electrons flow from the first can along the pencil graphite to the second can and the second can through the calculator and back to the graphite pencil in the first tin.
The salt dissolved in water allows the electrons to be transferred from the graphite to the inner surface of the can.
Oxygen dissolved in water comes from the air. That's why this type of battery is called oxy-aluminum batteries.

They will also need and are not included in the kit: 2 empty, clean aluminum cans, sharpener, water, salt, small Phillips screwdriver.