DP Chemistry (last assessment 2024)

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Question 18M.3.hl.TZ2.16

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Date May 2018 Marks available [Maximum mark: 5] Reference code 18M.3.hl.TZ2.16
Level hl Paper 3 Time zone TZ2
Command term Calculate, Explain Question number 16 Adapted from N/A
16.
[Maximum mark: 5]
18M.3.hl.TZ2.16

Nuclear power is another source of energy.

235U atoms can be used in nuclear reactors whereas 238U cannot. A centrifuge is used to separate isotopes.

(c.i)

Calculate the relative rate of effusion of 235UF6(g) to 238UF6(g) using sections 1 and 6 of the data booklet.

[2]

Markscheme

Mr(235UF6) = 235 + (19.00 × 6)/349

OR

Mr(238UF6) = 238 + (19.00 × 6)/352

 

« rate of effusion of   235 U rate of effusion of   238 U = 352 349 = » 1.004

 

Award [2] for correct final answer.

Do not accept “1.00” OR “0.996”.

[2 marks]

(c.ii)

Explain, based on molecular structure and bonding, why diffusion or centrifuging can be used for enrichment of UF6 but not UO2.

[3]

Markscheme

UF6: Structure: octahedral «solid»/square bipyramidal «solid»/«simple» molecular solid/simple molecule AND Bonding: covalent

UO2: Structure: crystal/lattice/network «solid»/«resembles» fluorite AND Bonding: «partly» covalent

UF6 sublimes/evaporates/boils at low temperature

 

Accept “UF6: Structure: octahedral «solid»/square bipyramidal «solid»/«simple» molecular solid/simple molecule AND weak intermolecular/London/dispersion/van der Waals’/vdW forces”.

Accept “non-polar molecule” for “«simple» molecular solid”.

Accept “giant molecular” OR “macromolecular” for “network”.

Accept “ionic/electrostatic attractions «between ions»” for bonding in UO2.

Award M2 for “UO2: network covalent/covalent network/giant covalent” OR “UO2: network ionic/giant ionic”.

For M1 and M2 award [1 max] for two correct structures OR two bonding types.

Accept any specified low temperature in the range 56–65 °C.

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