What are catalysts?

5 marks · Hard

A student investigates the reaction below:

(a)

Describe how the student could show that manganese(IV) oxide acts as a catalyst in this reaction.

[2 marks]

(b)

After the reaction, the student filters, dries, and reweighs the manganese(IV) oxide. The mass is unchanged. Explain why this result supports the conclusion that manganese(IV) oxide is a catalyst.

[2 marks]

(c)

State why only a small amount of catalyst is usually needed for a reaction.

[1 mark]

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

Show answer

(a) — · must show Compare reaction with and without MnO2: faster with catalyst, Observe oxygen produced more quickly or rapidly

(b) — · must show Catalyst not used up during the reaction, Mass unchanged: chemically unchanged at the end

Show mark scheme and worked solution

Marking points

M1 (a) · 1 mark · Describes comparing the reaction rate with and without manganese(IV) oxide (e.g., more gas produced or faster reaction with catalyst).

A1 (a) · 1 mark · States that more oxygen is produced quickly / reaction is faster with manganese(IV) oxide.

M2 (b) · 1 mark · Explains that the catalyst is not used up or mass is unchanged at end.

A2 (b) · 1 mark · Links unchanged mass to catalyst being chemically unchanged at the end.

B1 (c) · 1 mark · States that a catalyst can be reused or only a small amount is required because it is not used up.

Worked solution

a) Compare the rate of the decomposition of hydrogen peroxide with and without manganese(IV) oxide. The reaction is much faster and produces oxygen more quickly when the catalyst is present.

b) Since the mass of manganese(IV) oxide is the same before and after the reaction, it is not used up and remains chemically unchanged. This shows it acts as a catalyst, not as a reactant.

c) Because a catalyst is not used up in the reaction, a small amount can catalyse the reaction of many reactant particles.