DP Chemistry (last assessment 2024)
Question 19N.3.sl.TZ0.c
| Date | November 2019 | Marks available | [Maximum mark: 2] | Reference code | 19N.3.sl.TZ0.c |
| Level | sl | Paper | 3 | Time zone | TZ0 |
| Command term | Explain | Question number | c | Adapted from | N/A |
c.
[Maximum mark: 2]
19N.3.sl.TZ0.c
Stearic acid (Mr = 284.47) and oleic acid (Mr = 282.46) have the same number of carbon atoms. The structures of both lipids are shown in section 34 of the data booklet.
Explain why stearic acid has a higher melting point than oleic acid.
[2]
Markscheme
no kinks in chain/more regular structure
OR
straight chain
OR
no C=C/carbon to carbon double bonds
OR
saturated
OR
chains pack more closely together ✔
NOTE: Accept “greater surface area/electron density” for M1.
stronger London/dispersion/instantaneous induced dipole-induced dipole forces «between molecules» ✔
NOTE: Accept “stronger intermolecular/van der Waals’/vdW forces” for M2.
