Question 18M.3.sl.TZ2.6
| Date | May 2018 | Marks available | [Maximum mark: 11] | Reference code | 18M.3.sl.TZ2.6 |
| Level | sl | Paper | 3 | Time zone | TZ2 |
| Command term | Deduce, Determine, Explain, Identify, Outline | Question number | 6 | Adapted from | N/A |
Lipids provide energy and are an important part of a balanced diet.
Identify the type of chemical reaction that occurs between fatty acids and glycerol to form lipids and the by-product of the reaction.
[2]
Type of reaction:
condensation
OR
esterification/triesterification
OR
nucleophilic substitution/nucleophilic displacement/SN2
By-product:
water/H2O
Do not accept just “substitution/displacement”.
[2 marks]
Arachidonic acid is a polyunsaturated omega-6 fatty acid found in peanut oil.
Determine the number of carbon–carbon double bonds present if the iodine number for the compound is 334. (Arachidonic acid Mr = 304.5)
[2]
ALTERNATIVE 1
« =» 1.32 AND « =» 0.328
« ≈» 4
ALTERNATIVE 2
«334 × ≈» 1017
« ≈» 4
Award [2] for correct final answer.
[2 marks]
Deduce the structure of the lipid formed by the reaction between lauric acid and glycerol (propane-1,2,3-triol) using section 34 of the data booklet.
[2]
glycerol backbone
ester formula AND linkage
Accept a skeletal structure.
Penalize missing hydrogens or incorrect bond connectivities once only in Option B.
Accept condensed formula for ester.
[2 marks]
Outline one impact food labelling has had on the consumption of foods containing different types of lipids.
[1]
has affected consumption of trans-fats/cis-fats/saturated fats/unsaturated fats/hydrogenated/artificially altered fats
OR
reduce/eliminate trans-fats/increase in cis-fats
OR
reduce/eliminate saturated fats
OR
increase unsaturated fats
Do not accept “decrease in fat” alone.
Accept “lipid” for “fats”.
[1 mark]
Determine, to the correct number of significant figures, the energy produced by the respiration of 29.9 g of C5H10O5.
ΔHc (C5H10O5) = 205.9 kJ mol−1
[2]
« =» 0.199 «mol»
«0.199 mol × 205.9 kJ mol–1 =» 41.0 «kJ»
Ignore significant figures in M1.
Award [2] for correct final answer.
Award [1 max] for incorrect significant figures in final answer.
[2 marks]
Explain why lipids provide more energy than carbohydrates and proteins.
[2]
ratio of oxygen to carbon in lipids lower
OR
lipids less oxidized
OR
lipids more reduced
more energy per mass/g released when lipids are oxidized
Accept “«average» oxidation number of carbon in linoleic acid is lower” for M1.
[2 marks]