| Date | May 2019 | Marks available | 2 | Reference code | 19M.3.sl.TZ1.10 |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | 10 | Adapted from | N/A |
Question
Ascorbic acid and retinol are two important vitamins.
Explain why ascorbic acid is soluble in water and retinol is not. Use section 35 of the data booklet.
Markscheme
ascorbic acid: many hydroxyl/OH groups AND retinol: few/one hydroxyl/OH group
OR
ascorbic acid: many hydroxyl/OH groups AND retinol: long hydrocarbon chain [✔]
ascorbic acid: «many» H-bond with water
OR
retinol: cannot «sufficiently» H-bond with water [✔]
Note: Do not accept “OH−/hydroxide”.
Examiners report
Another instance where candidates insist on discussing water solubility in terms of polarity or hydrophilicity rather than its fundamental dependence on the presence of sufficient groups that can form hydrogen bonds to water. A few however gained a mark through pointing out the significance of the –OH groups in ascorbic acid and the long hydrocarbon chain in retinol.
Syllabus sections
- 20N.3.sl.TZ0.7a: The diverse functions of biological molecules depend on their structure and shape. Classify...
- 19N.3.hl.TZ0.14c: Vitamins are organic compounds essential in small amounts. State the name of one functional...
- 19N.3.sl.TZ0.10a: State the name of one functional group common to all three vitamins shown in section 35 of...
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19M.3.hl.TZ1.13:
Ascorbic acid and retinol are two important vitamins.
Explain why ascorbic acid is soluble in water and retinol is not. Use section 35 of the data booklet.
-
18N.3.sl.TZ0.5b:
Suggest why it is advisable for those living in northerly or southerly latitudes (that is away from the equator) to take vitamin D supplements during the winter.
-
19M.3.hl.TZ2.11c:
Lecithin aids the body’s absorption of vitamin E.
Suggest why vitamin E is fat-soluble.
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19M.3.sl.TZ2.7d:
Lecithin aids the body’s absorption of vitamin E.
Suggest why vitamin E is fat-soluble.
- 17N.3.sl.TZ0.10b: State one function of vitamin D in the body.
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17M.3.sl.TZ1.13d:
The solubility of a vitamin depends on its structure.
Identify the vitamin given in section 35 of the data booklet that is the most soluble in water.
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18M.3.sl.TZ1.7c.ii:
Predict the solubility of retinol (vitamin A) in body fat, giving a reason. Use section 35 of the data booklet.
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18M.3.sl.TZ2.9:
Explain the solubility of vitamins A and C using section 35 of the data booklet.
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17M.3.sl.TZ2.11:
Suggest, in terms of its structure, why vitamin D is fat-soluble using section 35 of the data booklet.
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17N.3.sl.TZ0.10a:
Explain, at the molecular level, why vitamin D is soluble in fats. Use section 35 of the data booklet.
- 20N.3.hl.TZ0.8a: The diverse functions of biological molecules depend on their structure and shape. Classify...
