Lab Preparation of O₂ (No Heat)
Hydrogen peroxide decomposed by manganese dioxide · collected over water
Apparatus Required
- Conical flask (with side arm / fitted with cork)
- Thistle funnel / dropping funnel
- Delivery tube
- Water trough (pneumatic trough)
- Inverted gas jar (filled with water)
- Beehive shelf
- Glowing splint
Chemicals Required
- Hydrogen peroxide (H₂O₂) — 20 vol.
- Manganese dioxide (MnO₂) — catalyst
Chemical Reaction
2H₂O₂ → 2H₂O + O₂↑
(MnO₂ catalyst, no heat)
Hydrogen peroxide decomposes slowly on its own; MnO₂ greatly speeds up the reaction. Oxygen gas is evolved without heating.
Key Points
- O₂ is colourless, odourless
- Collected by downward displacement of water
- Supports combustion — relights a glowing splint
- MnO₂ is a catalyst — remains unchanged
- No external heat required — safer method
Safety Precautions
Wear safety goggles · H₂O₂ is an irritant · avoid skin contact · MnO₂ dust may irritate respiratory tract · work in a well-ventilated area.