Question 20N.2.sl.TZ0.2
| Date | November 2020 | Marks available | [Maximum mark: 6] | Reference code | 20N.2.sl.TZ0.2 |
| Level | sl | Paper | 2 | Time zone | TZ0 |
| Command term | Deduce, Draw, Justify, Predict | Question number | 2 | Adapted from | N/A |
Compound A is in equilibrium with compound B.
Predict the electron domain and molecular geometries around the oxygen atom of molecule A using VSEPR.
[2]
Electron domain geometry: tetrahedral ✔
Molecular geometry: bent/V-shaped ✔
Half of the candidates answered correctly. The rest of the candidates often answered the question in terms of the carbon atom indicating that they did not read the question carefully.
The IR spectrum of one of the compounds is shown:
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Deduce, giving a reason, the compound producing this spectrum.
[1]
B AND absorption/
OR
B AND absence of ✔
Accept any value between .
About 50% of the candidates answered correctly. Quite a few, however, gave compounds other than A or B, indicating not reading the question properly or being confused by the skeletal formulas given in the question.
Compound A and B are isomers. Draw two other structural isomers with the formula .
[2]
Accept any two isomers except for propanone and propen-2-ol:
✔✔
Penalize missing hydrogens in displayed structural formulas once only.
Nearly half of the candidates gave two correct isomers. Propanal was often given as one of the isomers. Some candidates repeated the compounds given in the question and a few gave structures with 5 bonds on a carbon atom.
The equilibrium constant, , for the conversion of A to B is in water at .
Deduce, giving a reason, which compound, A or B, is present in greater concentration when equilibrium is reached.
[1]
AND is greater than /large ✔
Half of the candidates answered correctly. A common mistake was K > 0 instead of K > 1.