Splitting Water: Electrolysis Experiment

Is it possible to break water? In a sense, that's what electrolysis does. Electrolysis uses electricity to split water into its two ingredients: hydrogen and oxygen. Try it out with a battery and a couple pencils! (Adult supervision required.)

Materials

• 6-volt or 9-volt battery
• Two alligator clip leads or insulated wire
• Beaker or glass
• Piece of thin cardboard or cardstock
• Two #2 pencils 

What to do:

1. Fill the beaker or glass with warm water.
2. Carefully remove the erasers and metal sleeves so you can sharpen both ends of each pencil.
3. Cut a piece of the cardboard to fit over the beaker, then punch two holes in the center of the cardboard about an inch apart. Push the pencils through the holes and set them in the glass. They should extend into the water, but not touch the bottom of the glass. The cardboard will hold them in place.
4. Connect each pencil to the battery with an alligator clip lead attached to the exposed graphite (pencil lead). If you don't have alligator clip leads, use two lengths of wire and strip an inch of insulation off each end. Wrap the wire around the graphite of each pencil and connect the wires to the battery. You may need to use tape to hold the wires in place.

What's happening?

As soon as you connect the wires to the battery, you will see bubbles appearing around each of the pencil tips in the water and floating upward. Those bubbles are the components of water €”hydrogen and oxygen gas €”that have been split apart by the electricity as it travels through the water from one pencil to the other. The pencil attached to the negative terminal of the battery collects hydrogen gas while the one connected to the positive terminal collects oxygen. Does one pencil collect more bubbles than the other? Which one? Why do you think this is? (Hint: Water's chemical name is H₂O because it has two hydrogen atoms to every one oxygen atom.)

With some electrolysis equipment you can collect the two gases and test their different reactions to a flame.

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