Number 8: Splitting water

If there's a chemical formula we all remember it the one for water, good old H₂O;  two hydrogens and an oxygen. Well its really easy to split water up and liberate the hydrogen and oxygen as gases. The process is called electrolysis and all you need is....

What you'll need:

• One 9V battery (those square ones)
• 2 lengths of insulated wire
• A pencil
• A bowl of water
• Table salt
• A box cutter knife

Safety:
Watch out with the knife. Best get an adult to use it.


What to do:
1. First you need to get the lead ¹ out of the pencil. To do this its best to carefully whittle the pencil with a pen knife or box cutter.
2. Strip about 2cm of the insulation from both ends of both wires.
3. Take one of the wires and wrap one end around a terminal of the battery and the other end around the graphite from the pencil. Repeat with the other wire. BE CAREFUL not to short circuit the battery by letting a bit of wire touch both battery terminals.
4. Dissolve a teaspoon of salt in the bowl of water.
5. Put the graphite rods into the water.

6. Take a close look at the graphite rods. You should notice bubbles forming on them.

What's going on?
We all learnt at school that water is made up of 2 hydrogen atoms and 1 oxygen atom, so a molecule of water has the formula H₂O. But this isn't the whole picture, because in your bowl of water a lot of it isn't actually in the molecular (H₂O) form. Instead it splits up into H⁺ and OH^-. These are called ions. The + symbol on H⁺ means the hydrogen is positively charged because its missing its electron, meanwhile the - symbol on the OH^- means the OH ion is negatively charged because it has gained an electron.

Electricity it basically made up of moving electrons and ions. So electrons flow out of the negative terminal of the battery and in at the positive terminal. In the experiment we've just done the electrons flow down the wire to the graphite electrode and then join up with the H⁺ , this turns the ion back into molecular hydrogen (H₂). Hydrogen is a gas so it forms as bubbles on the electrode.  The opposite happens on the other electrode, here the extra electron on the OH^- flows up the wire leaving another H⁺ and molecular oxygen (O₂) gas.

You might have noticed that there are more bubbles on one electrode that the other. Thats because there is twice as much hydrogen than oxygen in water, so you also make twice as much hydrogen gas.


What's the point?
Hydrogen could well be the fuel of the future. The idea is that when we run out of fossil fuels we'll be able to replace petrol and oil with hydrogen. And this is how the hydrogen will be made. The only problem is that we need a source of electricity to split the water up and at the moment most of our electricity comes from burning fossil fuels. But if you hook up our setup to a wind turbine or a solar panel then the problem is solved!






1 Actually its graphite, not lead in pencils. And contrary to popular belief pencils never had lead in them. The name comes from 'black lead' which was mined near Keswick in the UK's Lake District. The Grey Knotts mines in the hill around Keswick are the only natural source of solid graphite in the world. Which meant that until an artificially way of making solid graphite rods was invented the lead in every pencil in the world came from Keswick.