Question 18M.3.hl.TZ2.c.ii
| Date | May 2018 | Marks available | [Maximum mark: 3] | Reference code | 18M.3.hl.TZ2.c.ii |
| Level | hl | Paper | 3 | Time zone | TZ2 |
| Command term | Explain | Question number | c.ii | Adapted from | N/A |
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.
Explain, based on molecular structure and bonding, why diffusion or centrifuging can be used for enrichment of UF6 but not UO2.
[3]
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.
