Question 23M.3.HL.TZ2.8
| Date | May 2023 | Marks available | [Maximum mark: 6] | Reference code | 23M.3.HL.TZ2.8 |
| Level | HL | Paper | 3 | Time zone | TZ2 |
| Command term | Calculate, Compare, Explain | Question number | 8 | Adapted from | N/A |
Lipids are another group of biomolecules.
Compare the hydrolytic and oxidative rancidity and contrast the site where the chemical changes occur.
Compare rancidity: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Contrast reaction site: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
[2]
Compare rancidity:
«both produce» disagreeable smell/taste/texture/appearance ✓
Contrast reaction site:
hydrolytic reaction occurs at ester link/COOC link AND oxidative reaction occurs at carbon-carbon double bond/C=C ✓
Do not accept “double bond” alone for oxidative reaction site.
Calculate the iodine number for ozubondo acid, C21H33COOH.
Mr = 330.56
[2]
5 C=C ✓
«100 g/330.56 g mol−1 × 5 × 253.8 g mol−1 =» 383.89 «g I2» ✓
Award [2] for correct final answer.
Explain two ways in which carbohydrates and lipids differ as sources of energy.
[2]
lipids are more reduced AND release/store more energy than carbohydrates «per gram» ✓
lipids are less «water» soluble AND energy is released slower/less available than in carbohydrates ✓
Accept converse arguments.
Award [1 max] for “carbohydrates used for short-term energy supply AND lipids used for long-term energy supply”
OR
“lipids more reduced AND less «water» soluble”.