| Date | May 2009 | Marks available | 3 | Reference code | 09M.3.sl.TZ2.F1 |
| Level | SL | Paper | 3 | Time zone | TZ2 |
| Command term | State and explain | Question number | F1 | Adapted from | N/A |
Question
Describe the chemical composition of a triglyceride.
[1]
a.
The following two structures represent isomers of a fatty acid.
State and explain which isomer has the higher melting point.
[3]
b.
Markscheme
ester of glycerol/propan-1,2,3-triol and three fatty acids/long chain carboxylic acids;
a.
II;
more straight molecule/greater surface area hence greater distortion of electron cloud / allows closer packing of fatty acids for trans / does not allow closer packing for cis isomers / OWTTE;
trans greater van der Waals’ forces / cis less van der Waals’ forces;
Accept London/dispersion forces.
b.
Examiners report
Many candidates knew the structure of triglycerides.
a.
Most candidates identified structure II as the one with the highest melting point and many gave the correct reason.
b.
Syllabus sections
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