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Activity 1.4b — Electrolysis of Water
Electrolysis of water: pass electricity through acidulated water and watch it split into H₂ (at the cathode) and O₂ (at the anode) in a 2:1 volume ratio. The third type of decomposition reaction — driven by electricity.
How To Perform
1
Fill with Acidulated Water
Water with a few drops of dilute H₂SO₄ (provides ions to conduct current).
2
Connect the Battery
Cathode (−) on the left, anode (+) on the right, via conducting wires.
3
Switch On the Current
Electrolysis begins: H₂ evolves at the cathode, O₂ at the anode.
4
Observe the 2:1 Ratio
The cathode arm fills with twice as much gas as the anode arm.
5
Test for H₂ and O₂
Pop test at cathode, glowing splint rekindles at anode.
6
Classify the Reaction
Water decomposes using electrical energy — what type is this?
⚠️ Safety Notes
- •Use only LOW voltage DC (6V or less) — household mains AC is dangerous and will not split water cleanly.
- •H₂ is flammable and forms explosive mixtures with air — keep flames away during collection.
- •Use a well-ventilated area — both H₂ and O₂ support combustion.