Step 1: choose the reaction
Oxygen can be made in several ways. We compare them with questions: Is it safe? Does it need a flame? Is it easy to control? Is the gas pure?
| Method | Equation | Heat? |
|---|---|---|
| H₂O₂ with MnO₂ catalyst | 2H₂O₂ → 2H₂O + O₂ | No |
| Heating KMnO₄ | 2KMnO₄ → K₂MnO₄ + MnO₂ + O₂ | Yes |
| Heating KClO₃ with MnO₂ | 2KClO₃ → 2KCl + 3O₂ | Yes |
| Electrolysis of water | 2H₂O → 2H₂ + O₂ | Needs electricity and gives hydrogen too |
For a simple supplier, H₂O₂ and MnO₂ wins: no flame, easy to start and stop, and only water is left behind.
The catalyst: manganese dioxide
A catalyst speeds up a reaction but is not used up. Hydrogen peroxide breaks down very slowly by itself. MnO₂ makes it fast. After the reaction you can filter and dry the black powder and its mass is the same. More catalyst or a warmer solution gives a faster flow of bubbles.
Step 2: design the supplier
Our design has three parts.
- Reaction bottle with H₂O₂ solution and a little MnO₂. Add the peroxide slowly through a funnel or dropper so you control the speed.
- Water (wash) bottle. Gas enters through a long tube under the water and leaves by a short tube. It cools the gas, adds moisture, and the bubbles act as a flow counter.
- Outlet tube to a small jar or nozzle.
Keep all joints tight so gas cannot leak. A narrow, open outlet stops pressure from building up.
Step 3: test it
Hold a glowing splint (burning stick blown out so it only glows) at the outlet. If it bursts into flame again, the gas is oxygen. Also count bubbles per second at different amounts of MnO₂ and write a small table. Check that the flow can be stopped by stopping the peroxide.
Test for leaks by watching the bubbles: if the outlet flow is weak but the reaction bottle bubbles fast, gas is escaping somewhere.
Safety and limits
- Use dilute H₂O₂ (about 3 percent, the type for cleaning wounds). Strong peroxide burns skin.
- Never use flames near the outlet. Oxygen makes fires burn fiercely.
- Wear eye protection, and work with a teacher or adult.
- This model makes a little gas for a demonstration. It is not a medical device and cannot replace real oxygen.
Try it: bubble counter
Using a small bottle of peroxide solution and a pinch of dry yeast (a natural catalyst) in a bowl-sized glass, watch the foam. Compare with and without yeast. Which one makes bubbles faster? Predict first, then check. Do this with an adult.
Key formulas and definitions
- 2H₂O₂ → 2H₂O + O₂ (MnO₂ catalyst)
- 2KMnO₄ → K₂MnO₄ + MnO₂ + O₂ (heat)
- 2KClO₃ → 2KCl + 3O₂ (heat, MnO₂)
- 68 g H₂O₂ gives 32 g O₂
- 1 mole of gas at STP = 22.4 L
Worked examples
1. Why choose H₂O₂ with MnO₂ for a simple school supplier?
It needs no heating, is easy to control, and leaves only water and the catalyst behind.
2. What does the water bottle do?
It cools the gas, adds moisture, and lets you count bubbles to see the flow rate.
3. How do you test the gas is oxygen?
Hold a glowing splint at the outlet. It relights if the gas is oxygen.
4. How much O₂ comes from 34 g of pure H₂O₂? (H₂O₂ = 34 g/mol, O₂ = 32 g/mol)
34 g is 1 mol. 2 mol H₂O₂ give 1 mol O₂, so 1 mol gives 0.5 mol O₂ = 16 g.
5. MnO₂ before and after has the same mass. Why?
It is a catalyst. It speeds the reaction but is not used up.
6. Volume of O₂ at STP from 3.4 g of H₂O₂?
3.4 / 34 = 0.1 mol H₂O₂. This gives 0.05 mol O₂. Volume = 0.05 × 22.4 = 1.12 L.
Common mistakes
- Calling MnO₂ a reactant. It is a catalyst and is not used up.
- Using strong H₂O₂. It burns skin and reacts too violently. Use dilute solution.
- Testing with a burning splint instead of a glowing one. Use a glowing splint to test for oxygen.
- Bringing a flame near the oxygen outlet, which is dangerous.