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Date May 2018 Marks available 1 Reference code 18M.3.sl.TZ2.6
Level SL Paper 3 Time zone TZ2
Command term Outline Question number 6 Adapted from N/A

Question

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]
a.

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]
b.

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]
c.

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

[1]
d.

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

ΔH(C5H10O5) = 205.9 kJ mol−1

[2]
e.

Explain why lipids provide more energy than carbohydrates and proteins.

[2]
f.

Markscheme

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]

a.

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]

b.

M18/4/CHEMI/SP3/ENG/TZ2/06.c/M

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]

c.

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]

d.

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

e.

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]

f.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.
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d.
[N/A]
e.
[N/A]
f.

Syllabus sections

Options » B: Biochemistry » B.3 Lipids
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