Question 22M.2.sl.TZ2.c
| Date | May 2022 | Marks available | [Maximum mark: 2] | Reference code | 22M.2.sl.TZ2.c |
| Level | sl | Paper | 2 | Time zone | TZ2 |
| Command term | Describe | Question number | c | Adapted from | N/A |
Carbon forms many compounds.
Describe a test and the expected result to indicate the presence of carbon–carbon double bonds.
[2]
ALTERNATIVE 1:
Test:
add bromine «water»/Br2 (aq) ✔
Result:
«orange/brown/yellow» to colourless/decolourised ✔
Do not accept “clear” for M2.
ALTERNATIVE 2:
Test:
add «acidified» KMnO4 ✔
Result:
«purple» to colourless/decolourised/brown ✔
Accept “colour change” for M2.
ALTERNATIVE 3:
Test:
add iodine / ✔
Result:
«brown» to colourless/decolourised ✔
About half of the candidates gave the bromine water test with the correct results. Iodine and KMnO4 were rarely seen in the scripts. There were candidates who used the term “clear” to mean “colourless” which was not accepted. Some candidates referred to the presence of UV light in a correct way and others in an incorrect way which was not penalized in this case. 10% of the candidates left the question blank. The most common incorrect answer was in terms of the IR absorptions. Other candidates referred to enthalpies of combustion and formation.