Question 19M.3.sl.TZ1.9a
| Date | May 2019 | Marks available | [Maximum mark: 3] | Reference code | 19M.3.sl.TZ1.9a |
| Level | sl | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | a | Adapted from | N/A |
The main fatty acid composition of cocoa butter and coconut oil is detailed below.
The melting points of cocoa butter and coconut oil are 34 °C and 25 °C respectively.
Explain this in terms of their saturated fatty acid composition.
[3]
coconut oil has higher content of lauric/short-chain «saturated» fatty acids
OR
cocoa butter has higher content of stearic/palmitic/longer chain «saturated» fatty acids [✔]
longer chain fatty acids have greater surface area/larger electron cloud [✔]
stronger London/dispersion/instantaneous dipole-induced dipole forces «between triglycerides of longer chain saturated fatty acids» [✔]
Note: Do not accept arguments that relate to the melting points of saturated and unsaturated fats.
A classic instance of candidates answering the question they thought (or hoped?) they had been asked rather than the one that was asked. Almost all answers referred to the differing amounts of saturated and unsaturated fatty acids present, totally ignoring the fact that the question clearly stated “their saturated fatty acid composition”, where the relative lengths of the chains was the key point. Nevertheless some who went on to discuss the nature of the intermolecular forces between the chains gained some credit.
