DP Chemistry (last assessment 2024)

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Question 19N.3.sl.TZ0.3

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Date November 2019 Marks available [Maximum mark: 5] Reference code 19N.3.sl.TZ0.3
Level sl Paper 3 Time zone TZ0
Command term Describe, Distinguish, Explain, State Question number 3 Adapted from N/A
3.
[Maximum mark: 5]
19N.3.sl.TZ0.3

Catalysts are commonly used in industry.

(a)

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

[2]

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”.

(b)

Distinguish between heterogeneous and homogeneous catalysts, giving one difference.

[1]

Markscheme

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”.

(c)

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]

Markscheme

high temperature used ✔

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

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