| Date | November 2016 | Marks available | 2 | Reference code | 16N.3.sl.TZ0.12 |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | Discuss | Question number | 12 | Adapted from | N/A |
Question
Auto-ignition of hydrocarbon fuel in a car engine causes “knocking”. The tendency of a fuel to knock depends on its molecular structure.
Discuss how the octane number changes with the molecular structure of the alkanes.
[2]
a.
Catalytic reforming and cracking reactions are used to produce more efficient fuels. Deduce the equation for the conversion of heptane to methylbenzene.
[1]
b.
Markscheme
«tends to» decrease with longer/larger/heavier alkanes
«tends to» increase with bulkier/more branched alkanes
Accept “octane number decreases with the separation between branches” OR “increases with the more central position of branches”.
Accept converse arguments.
a.
C7H16 → C6H5CH3 + 4H2
Accept “C7H8” for “C6H5CH3”.
b.
Examiners report
[N/A]
a.
[N/A]
b.
