Electrolysis of Water — Interactive Diagram
Watch an electric current split water into hydrogen and oxygen — and see why you always get twice as much hydrogen.
TL;DR: Watch an electric current split water into hydrogen and oxygen — and see why you always get twice as much hydrogen.
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Electrolysis of Water: Watch an electric current split water into hydrogen and oxygen — and see why you always get twice as much hydrogen.
Why it matters: Electrolysis of water is a classic decomposition reaction and a common practical/viva and exam question.
Electrolysis of Water — Step by Step
- Two electrodes are placed in water (with a little acid to conduct) and connected to a battery. Current begins to flow.
- Bubbles of gas form on both electrodes. HYDROGEN (H₂) collects at the CATHODE (–); OXYGEN (O₂) at the ANODE (+).
- You always collect TWICE as much hydrogen as oxygen (2:1) — because water is H₂O. Reaction: 2H₂O → 2H₂ + O₂.
Quick Notes — the Exam Crux
- Passing electricity through water (with a little acid to help conduct) breaks it into hydrogen and oxygen gas.
- Hydrogen (H₂) collects at the CATHODE — the negative electrode.
- Oxygen (O₂) collects at the ANODE — the positive electrode.
- The volume of hydrogen is DOUBLE the volume of oxygen (2 : 1), because water is H₂O — two H for every O.
- This is a decomposition reaction: 2H₂O → 2H₂ + O₂ (energy from electricity).
Remember It (Memory Trick)
"Hydrogen doubles at the negative." At the cathode (–) you collect H₂; at the anode (+) you collect O₂ — in a 2 : 1 volume ratio.
Real-Life Example
The same idea powers hydrogen fuel: splitting water with (ideally solar) electricity gives clean hydrogen gas that can run a fuel-cell bus, releasing only water when burnt.
Test Yourself
Which gas is collected at the cathode, and how much compared to the other?
Hydrogen (H₂), at the negative cathode — and its volume is double that of oxygen.
Why is the hydrogen-to-oxygen volume ratio 2 : 1?
Because water is H₂O: each molecule has two hydrogen atoms for every one oxygen atom.
What type of reaction is electrolysis of water?
A decomposition reaction (specifically electrolytic decomposition), driven by electrical energy.
More Visual Lessons
- The Water Cycle
- States of Matter
- Life Cycle of a Butterfly
- Phases of the Moon
- The Solar System
- The Rock Cycle
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