Splitting Water with Electricity

Why it matters

You can boil water forever and it stays water. But pass an electric current through it and it splits into two gases — one of which burns with a pop, the other relights a glowing splinter. Electricity does what heat cannot.

The idea in plain words

Balance it yourself: count the hydrogen atoms on each side first, then let oxygen settle the account. No shortcuts — the coefficients are yours to find.

Predict first

Electrolysis of water gives hydrogen and oxygen. In what volume ratio?

2H₂O → 2H₂ + O₂ — read the coefficients: two hydrogen molecules for every oxygen. The equation predicted the experiment.

• 1 : 1, equal partners
• 2 volumes hydrogen : 1 volume oxygen — correct
• 1 hydrogen : 2 oxygen
• It varies with the battery

What you do

Switch on the current. Twice as much gas collects at one electrode — the equation told you which.

Check yourself

Boiling water makes steam; electrolysing water makes H₂ and O₂. Which is the chemical change?

Steam is still H₂O — physical. Electrolysis produces NEW substances with new properties — chemical. Bubbles alone prove nothing; identity does.

Why is a little acid added to the water before electrolysis?

Pure water is a very poor conductor. A pinch of acid provides ions to carry the current — the gases still come from the water itself.

This reaction is classified as…

One compound → two simpler substances = decomposition. The energy source here is electricity, so: electrolytic decomposition.

• Boiling
• Electrolysis — correct
• Both
• Neither
• To make the gases smell detectable
• Pure water barely conducts electricity; the acid lets current flow — correct
• Acid supplies the hydrogen
• To stop the water boiling
• combination
• decomposition (electrolytic) — correct
• displacement
• neutralisation