During the electrolysis of water, why is the volume of gas collected at one electrode exactly double that collected at the other? Name both gases and identify which electrode produces the larger volume.
Generated by claude-sonnet-4-6 · 2026-06-26 00:54 · grounding rag
Model Answer
Water (H₂O) is composed of hydrogen and oxygen in the ratio 2:1 by volume. During electrolysis, water molecules break down as:
$$2H_2O \rightarrow 2H_2 + O_2$$
Since two molecules of hydrogen are produced for every one molecule of oxygen, the volume of hydrogen collected is exactly double that of oxygen.
- Gas at the cathode (negative electrode): Hydrogen (H₂) — larger volume
- Gas at the anode (positive electrode): Oxygen (O₂) — smaller volume
The cathode produces the larger volume of gas.
Explanation
- The key reason is the 2:1 molar (and volume) ratio of H to O in water — examiners expect you to state this clearly.
- Always identify which electrode produces which gas: cathode → hydrogen, anode → oxygen. This is a common 1-mark direct question.
- You may write the decomposition equation for full marks; it shows the 2:1 ratio directly.
- The source passages provided do not cover this topic directly, so this answer draws on standard CBSE Class 10 Science (Chapter 1 – Chemical Reactions and Equations / Chapter 2 knowledge of water electrolysis as taught in the course).