Electrolysis of Water
Observe the electrolysis of water using a Hoffman apparatus. When electric current is passed through water, it decomposes into hydrogen gas (H₂) at the cathode and oxygen gas (O₂) at the anode.
When electric current is passed through water (with added electrolyte), bubbles of gas form at both electrodes. Twice as much hydrogen gas is produced compared to oxygen gas.
The Science Behind Water Electrolysis
Electrolysis is the decomposition of a compound using electricity:
- Pure water doesn't conduct electricity well, so an electrolyte (like H₂SO₄ or NaOH) is added
- At the cathode (negative electrode): 2H₂O + 2e⁻ → H₂ + 2OH⁻
- At the anode (positive electrode): 4OH⁻ → O₂ + 2H₂O + 4e⁻
- The overall reaction: 2H₂O → 2H₂ + O₂
- Hydrogen gas volume is twice that of oxygen gas (2:1 ratio)
1. Water molecules are broken down into hydrogen and oxygen gases
2. Hydrogen ions (H⁺) move to the cathode, gain electrons to form H₂ gas
3. Hydroxide ions (OH⁻) move to the anode, lose electrons to form O₂ gas
4. The 2:1 volume ratio confirms the molecular composition of water (H₂O)
- Hydrogen production for fuel cells and industrial processes
- Oxygen generation in spacecraft and submarines
- Demonstration of stoichiometric relationships in chemistry
- Important industrial process for chemical manufacturing
