Question 18M.3.sl.TZ1.a.ii
| Date | May 2018 | Marks available | [Maximum mark: 2] | Reference code | 18M.3.sl.TZ1.a.ii |
| Level | sl | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | a.ii | Adapted from | N/A |
Palmitic acid has a molar mass of 256.5 g mol−1.
When a small amount of palmitic acid is placed in water it disperses to form a layer on the surface that is only one molecule thick. Explain, in terms of intermolecular forces, why this occurs.
[2]
Any two of:
–COOH/CO/OH/carboxylate/carboxyl/hydroxyl/hydroxy group forms hydrogen bonds/H-bonds to water
London/dispersion/instantaneous induced dipole-induced dipole forces occur between hydrocarbon chains
hydrocarbon chain cannot form hydrogen bonds/H-bonds to water
strong hydrogen bonds/H-bonds between water molecules exclude hydrocarbon chains «from the body of the water»
Accept “hydrophilic part/group forms hydrogen bonds/H-bonds to water”.
Accept “hydrophobic section” instead of “hydrocarbon chain”.
Award [1 max] for answers based on “the –COOH group being polar AND the hydrocarbon chain being non-polar”.
[2 marks]
