Laboratory Preparation of Oxygen (O₂)
Heating potassium chlorate with manganese dioxide · collected over water
Apparatus Required
- Hard-glass test tube (mouth tilted down)
- Bunsen burner
- Retort stand and clamp
- Delivery tube
- Water trough (pneumatic trough)
- Inverted gas jar (filled with water)
- Beehive shelf
- Glowing splint
Chemicals Required
- Potassium chlorate (KClO₃)
- Manganese dioxide (MnO₂) — catalyst
Chemical Reaction
2KClO3 → 2KCl + 3O2↑
(MnO₂ catalyst, heat)
Potassium chlorate decomposes on heating to form potassium chloride and oxygen gas. Manganese dioxide acts as a catalyst.
Key Points
- O₂ is colourless, odourless
- Collected by downward displacement of water
- Supports combustion — relights a glowing splint
- Test tube mouth tilted down to avoid water flowing back
- MnO₂ catalyst remains unchanged
Safety Precautions
Wear safety goggles · KClO₃ is a strong oxidising agent · avoid mixing with combustibles · do not point tube toward anyone · work in a well-ventilated area.