Question 19M.3.sl.TZ2.c
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.3.sl.TZ2.c |
| Level | sl | Paper | 3 | Time zone | TZ2 |
| Command term | Describe | Question number | c | Adapted from | N/A |
This question is about fuel for engines.
Hydrocarbons need treatment to increase their octane number to prevent pre-ignition (knocking) before they can be used in internal combustion engines.
Describe how this is carried out and the molecular changes that take place.
[2]
Any two of:
«hydrocarbons are heated with» catalyst [✔]
long chains break and reform
OR
branching/aromatization occurs
OR
isomerisation/reforming/platforming/cracking [✔]
zeolite separates branched from non-branched
OR
products are distilled
OR
«distillation» separates reformed and cracked products [✔]
Note: Accept a specific catalysis name or formula for M1 such as Pt/Re/Rh/Pd/Ir.
Students responded well to at least one mark of this question. There were several different ways to earn the 2 marks possible. The most common way students earned marks were by identifying the use of a catalyst and then the idea of the compound reforming into a smaller or branched compound. Very few students discussed the idea of purification or separation into individual compounds which is another important part of this process.
