Question 19M.3.hl.TZ2.c
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.3.hl.TZ2.c |
| Level | hl | 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/aromatisation 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 catalyst name or formula for M1 such as Pt/Re/Rh/Pd/Ir.
Candidates responded well to at least one mark of this question. There were several different ways to earn the two marks possible. The most common way candidates 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 candidates discussed the idea of purification or separation into individual compounds, which is another important part of this process.
