Identify the type of chemical reaction that occurs between fatty acids and glycerol to form lipids and the by-product of the reaction.

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 M_r = 304.5)

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.

Outline one impact food labelling has had on the consumption of foods containing different types of lipids.

Determine, to the correct number of significant figures, the energy produced by the respiration of 29.9 g of C₅H₁₀O₅.

ΔH_c (C₅H₁₀O₅) = 205.9 kJ mol⁻¹

Explain why lipids provide more energy than carbohydrates and proteins.

Type of reaction:

condensation

OR

esterification/triesterification

OR

nucleophilic substitution/nucleophilic displacement/S_N2

By-product:

water/H₂O

Do not accept just “substitution/displacement”.

[2 marks]

ALTERNATIVE 1

«\(\frac{{334}}{{253.8}}\) =» 1.32 AND «\(\frac{{100}}{{304.5}}\) =» 0.328

«\(\frac{{1.32}}{{0.328}}\) ≈» 4

ALTERNATIVE 2

«334 × \(\frac{{304.5}}{{100}}\) ≈» 1017

«\(\frac{{1017}}{{253.8}}\) ≈» 4

Award [2] for correct final answer.

[2 marks]

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]

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]

«\(\frac{{29.9{\text{ g}}}}{{150.15{\text{ g mo}}{{\text{l}}^{ - 1}}}}\) =» 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]

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]