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Date	November 2019	Marks available	1	Reference code	19N.3.sl.TZ0.9
Level	SL	Paper	3	Time zone	TZ0
Command term	Identify	Question number	9	Adapted from	N/A

Question

Stearic acid (M_r = 284.47) and oleic acid (M_r = 282.46) have the same number of carbon atoms. The structures of both lipids are shown in section 34 of the data booklet.

The iodine number is the number of grams of iodine which reacts with 100 g of fat. Calculate the iodine number of oleic acid.

[1]

State one impact on health of the increase in LDL cholesterol concentration in blood.

[1]

Explain why stearic acid has a higher melting point than oleic acid.

[2]

State one similarity and one difference in composition between phospholipids and triglycerides.

Similarity:

Difference:

[2]

d(i).

Identify a reagent that hydrolyses triglycerides.

[1]

d(ii).

Markscheme

«one C=C bond»
«1 mole iodine : 1 mole oleic acid»

« $\frac{{100 \times 253.80}}{{282.46}}$ =» 89.85 «g of I₂» ✔

NOTE: Accept “90 «g of I₂»”.

atherosclerosis/cholesterol deposition «in artery walls»/increases risk of heart attack/stroke/cardiovascular disease/CHD ✔

NOTE: Accept “arteries become blocked/walls become thicker”, “increases blood pressure”, OR “blood clots”.
Do not accept “high cholesterol” OR "obesity"

no kinks in chain/more regular structure
OR
straight chain
OR
no C=C/carbon to carbon double bonds
OR
saturated
OR
chains pack more closely together ✔

NOTE: Accept “greater surface area/electron density” for M1.

stronger London/dispersion/instantaneous induced dipole-induced dipole forces «between molecules» ✔

NOTE: Accept “stronger intermolecular/van der Waals’/vdW forces” for M2.

Similarity:

«derived from» propane-1,2,3-triol/glycerol/glycerin/glycerine

OR
«derived from» at least two fatty acids
OR
contains ester linkages
OR
long carbon chains ✔

NOTE: Do not accept “two fatty acids as both a similarity and a difference”.
Do not accept just “hydrocarbon/carbon chains”.

Difference:

phospholipids contain two fatty acids «condensed onto glycerol» AND triglycerides three
OR
phospholipids contain phosphate/phosphato «group»/residue of phosphoric acid AND triglycerides do not ✔

NOTE: Accept “phospholipids contain phosphorus AND triglycerides do not".
Accept “phospholipids are amphiphilic AND triglycerides are not” OR “phospholipids have hydrophobic tails and hydrophilic heads AND triglycerides do not”.

d(i).

«concentrated» NaOH (aq)/sodium hydroxide
OR
«concentrated» HCl (aq)/hydrochloric acid
OR
enzymes/lipases ✔

NOTE: Accept other strong acids or bases.

d(ii).