You will need:

• A glass of water
• Two pencils sharpened at both ends
• Either 9 volt battery or 9-12 V DC adapter.
• Some bits of wire
• Tape to fix things together
• A teaspoon-full of table salt

After you connect everything, bubbles will form at the tips of pencils immediately.

Oxygen gas bubbles (O₂) will form at + electrode named anode.

Hydrogen gas bubbles H₂ will form at - electrode named cathode. The amount will be twice the amount of O₂.

Pure water is an insulator and the electrolysis may proceed too slowly. Some will say Sulfuric acid or NaSo4 is better, but those are not readily available outside labs. Sulfuric acid is also dangerous to handle. Table salt will suffice for the purpose of this demonstration. Using NaCl as an electrolyte results in some impurity in the form of chlorine gas at anode but that should not be important for the purpose of this demo.

Some things to vary:

• Try stripping the pencil lead (graphite) from the wood to increase the area of contact with water.
• Try the to see what happens if you vary water temperature.