Splitting water with electricity

Freeze water and you get ice; boil it and you get vapour; warm the ice or cool the vapour and you get water back. Through all that, the water particles stay the same. What if we pass electricity through water?

Activity 8.3 is a teacher demonstration. Take care with the sulfuric acid, and don't use a lithium-ion battery. You need two small test tubes, a beaker or glass and a 9 V battery. Fill two-thirds of the beaker with water and add a few drops of dilute sulfuric acid. Fill both test tubes completely with water from the beaker.

Stand the battery in the beaker. Without spilling, turn a water-filled test tube upside down over each terminal, and wait.

Bubbles of gas form at both terminals and collect in the test tubes. After 10 to 15 minutes, compare the amounts: they are not equal.

Could the gas just be water vapour? No: vapour would have turned back into water. It must be something else.

Test each one, keeping your distance, by bringing a burning candle near the mouth of the tube:

So electricity splits water into two different gases: Water → Hydrogen + Oxygen. And look how unlike water they are: hydrogen is a fuel, oxygen helps burning, yet water puts fires out.