Oxygen Factory
Prepare oxygen in the lab using decomposition.
What this lesson covers
Why it matters
A bottle of clear liquid sits quietly on the bench, but inside, molecules are waiting to snap apart. Give them a nudge, and they release invisible bubbles of life-giving gas.
The idea in plain words
Balance check: 2 molecules of H₂O₂ yield 2 molecules of H₂O and 1 molecule of O₂.
Predict first
When hydrogen peroxide breaks down, what gas escapes the solution?
The O-O bond in peroxide is weak. When it breaks, oxygen atoms pair up to form O₂ gas, leaving behind water.
- Hydrogen gas
- Oxygen gas — correct
- Water vapour
- Carbon dioxide
What you do
Split hydrogen peroxide into water and oxygen. Drop in manganese dioxide (MnO₂) and it bubbles fast — a positive catalyst that speeds it up. Swap in phosphoric acid (H₃PO₄) and it barely fizzes — a negative catalyst that slows it down.
Check yourself
Which equation correctly represents this decomposition?
Hydrogen peroxide decomposes into water and diatomic oxygen gas. The equation must be balanced: 2H₂O₂ → 2H₂O + O₂.
What happens if you add phosphoric acid to the reaction?
Phosphoric acid acts as a negative catalyst (inhibitor), slowing down the decomposition of hydrogen peroxide.
Why is this reaction called 'decomposition'?
Decomposition involves a single reactant (H₂O₂) breaking apart into multiple products (H₂O and O₂).
- H₂O₂ → H₂ + O₂
- 2H₂O₂ → 2H₂O + O₂ — correct
- H₂O₂ → H₂O + O
- The reaction speeds up
- The reaction slows down — correct
- The reaction stops completely
- Two substances combine to form one
- One substance breaks down into two or more simpler substances — correct
- Electrons are transferred between substances