Question 22N.2.hl.TZ0.2
| Date | November 2022 | Marks available | [Maximum mark: 9] | Reference code | 22N.2.hl.TZ0.2 |
| Level | hl | Paper | 2 | Time zone | TZ0 |
| Command term | Annotate, Compare, Deduce, Determine, Draw, Explain, Justify, State | Question number | 2 | Adapted from | N/A |
Chloroquine is a medication used to prevent and treat malaria.
Draw a circle around the secondary amino group in chloroquine.
[1]
✔
About three quarters of students gained the mark by identifying the secondary amine group, though a significant number failed to answer the question.
State the number of sp2 hybridized carbons in chloroquine.
[1]
nine/9 ✔
About half of the candidates managed to deduce that chloroquine contained 9 sp2 hybridized carbons atoms.
Determine the index of hydrogen deficiency, IHD, of chloroquine.
[1]
seven/7 ✔
Less than a quarter of the students correctly calculate that the index of hydrogen deficiency (IHD) of chloroquine was 7 and the ability to do this seemed generally unrelated to overall performance on the rest of the paper.
Compare, giving a reason, the length of the carbon-nitrogen bond in the ring to the length of the carbon-N1 bond.
[1]
«bond in ring is» shorter AND more electrons are shared
OR
«bond in ring is» shorter AND partial double/multiple bonding/bond order 1.5 ✔
Almost everybody identified the C−N bond in the ring as being shorter, but only about half could justify this using bond order or the resonance/delocalization that produces it. A significant number incorrectly thought the one in the ring was a double bond.
Chloroquine can be synthesized by reacting 4,7-dichloroquinoline with another reactant, B.
4,7-dichloroquinoline chloroquine
Deduce the structure of B.
[2]
primary amine/–NH2 ✔
rest of structure ✔
Do not penalize using “N1”.
Students gained about two-thirds of the two marks. Many candidates did not realise the need for an atom to combine with the chlorine and hence terminated their molecule in "–NH". The majority were able to transpose the rest of the structure correctly but some, who unnecessarily chose to convert the skeletal formula into a structural one (about half), made simple errors.
This reaction can be done with a copper catalyst. State the ground-state electron configuration for copper.
[1]
1s22s22p63s23p64s13d10 / 1s22s22p63s23p63d104s1
OR
[Ar]4s13d10 / [Ar]3d104s1 ✔
Most students were aware that copper is one of the transition elements that does not have a full 4s level and gave the correct electron configuration.
Annotate the Maxwell–Boltzmann distribution curve showing the activation energies, Ea, for the catalysed and uncatalysed reactions.
[1]
both Ea values marked AND left one labelled catalysed ✔
Most candidates correctly annotated the given Maxwell-Boltzmann diagram to illustrate the effect of adding a catalyst, however a few drew a second curve.
Explain, referring to the Maxwell–Boltzmann distribution curve, the effect of a catalyst on a chemical reaction.
[1]
increases rate AND there is a greater area under the curve past activation energy
OR
increases rate AND greater proportion of/more molecules have «kinetic» E ≥ Ea «(cat) than Ea (uncat)» ✔
Do not award a mark for general statements about catalysts such as “provides alternative pathway” or “lowers Ea”.
Most knew about catalysts providing an alternative mechanism, but some failed to gain the mark by not referring back to the diagram, whilst others lost it through not stating catalysts cause the reaction rate to increase.