Transition Elements

Catalyst

Faster reactions, nothing used up

1. Magnetic properties and catalytic activity

Catalyst

2. The fizzing powder

Add a pinch of black manganese dioxide to hydrogen peroxide, and oxygen bubbles out fast. Is the black powder used up?

Pick the right answer

Predict: what happens to the manganese dioxide?
  • A. It is still there at the end, with the same mass
  • B. It turns into the oxygen gas
  • C. It is used up, little by little
الشرح
Manganese dioxide is a catalyst: it speeds up the release of oxygen from hydrogen peroxide and is still there at the end, with the same mass. Filtering, drying and weighing it shows this.

3. What a catalyst is

Catalyst

A substance that speeds up a chemical reaction without being used up or changed.
2H2O2 →[MnO2] 2H2O + O2
Manganese dioxide is written over the arrow
The catalyst is written over the arrow. It is not a reactant, and it is not a product.

4. Same mass at the end

  1. Weigh the MnO2 → Add it to H2O2: oxygen bubbles fast
  2. Add it to H2O2: oxygen bubbles fast → Filter, dry and weigh it again
  3. Filter, dry and weigh it again → Same mass as at the start
The catalyst is recovered unchanged

5. Try a new reaction

Pick the right answer

Oxygen is also made from potassium chlorate: 2KClO3 →[MnO2][Δ] 2KCl + 3O2. What happens to the MnO2?
  • A. It speeds up the reaction and is recovered unchanged
  • B. It is used up to make the oxygen
  • C. It turns into potassium chloride
الشرح
MnO2 is written over the arrow, so it is the catalyst: it speeds up the reaction and is recovered unchanged. The oxygen and the KCl both come from KClO3.

True or false?

Adding a catalyst makes a reaction produce more product.
الشرح
A catalyst changes how fast the product forms, not how much: the same amount of product forms, just faster.

Fill in the blanks

In a chemical equation, the catalyst is written _____ the arrow.
الشرح
The catalyst is written over the arrow, as MnO2 is.

6. Summary

  • A catalyst speeds up a chemical reaction without being used up.
  • It is written over the arrow, for example MnO2 in making oxygen from H2O2.
  • It is recovered with the same mass and gives no extra product.
Back to the hook: the black powder is still there, with the same mass.
Can you explain how weighing shows that MnO2 is a catalyst?
Reveal
Weigh the MnO2, add it to H2O2, then filter, dry and weigh it again: it has the same mass as at the start. It was not used up, yet oxygen bubbled out fast, so it is a catalyst.

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