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Date November 2019 Marks available 2 Reference code 19N.3.sl.TZ0.3
Level SL Paper 3 Time zone TZ0
Command term Explain Question number 3 Adapted from N/A

Question

Catalysts are commonly used in industry.

Describe how a heterogeneous catalyst provides an alternative pathway for a reaction.

[2]
a.

Distinguish between heterogeneous and homogeneous catalysts, giving one difference.

[1]
b.

Nanotubes are used to support the active material in nanocatalysts.

Explain why oxygen cannot be used for the chemical vapour deposition (CVD) preparation of carbon nanotubes.

[2]
c.

Markscheme

reactant(s) adsorb onto active sites/surface ✔

NOTE: Do not accept “absorb” for “adsorb” for M1.
Accept “bonds to” for “adsorb” for M1.


«reactant» bonds weakens «and products are desorbed» ✔

NOTE: Accept “bonds break/stretch «and products are desorbed»” for M2.
Award [1 max] for “lowers activation energy”.

a.

Any one of the following:

NOTE: Accept “heterogeneous adsorb reactants and homogeneous” but do not accept “absorb” for “adsorb”.
Accept “heterogeneous have active sites and homogeneous do not”.

b.

high temperature used ✔

oxygen/O2 reacts with carbon/C
OR
carbon dioxide/CO2 can form ✔

c.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.

Syllabus sections

Options » A: Materials » A.3 Catalysts
Options » A: Materials » A.6 Nanotechnology
Options » A: Materials
Options

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