| Date | November 2017 | Marks available | 1 | Reference code | 17N.3.sl.TZ0.8 |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | Suggest | Question number | 8 | Adapted from | N/A |
Question
Consider the following lipid and carbohydrate.
In order to determine the number of carbon-carbon double bonds in a molecule of linoleic acid, 1.24 g of the lipid were dissolved in 10.0 cm3 of non-polar solvent.
The solution was titrated with a 0.300 mol dm–3 solution of iodine, I2.
Determine the empirical formula of linoleic acid.
The empirical formula of fructose is CH2O. Suggest why linoleic acid releases more energy per gram than fructose.
State the type of reaction occurring during the titration.
Calculate the volume of iodine solution used to reach the end-point.
Outline the importance of linoleic acid for human health.
Markscheme
C9H16O
ratio of oxygen to carbon in linoleic acid lower
OR
linoleic acid less oxidized
OR
linoleic acid more reduced
Accept “«average» oxidation state of carbon in linoleic acid is lower”.
«electrophilic» addition/AE
OR
oxidation–reduction/redox
«\(\frac{{1.24\,{\text{g}}}}{{280.50\,{\text{g}}\,{\text{mo}}{{\text{l}}^{ - 1}}}}\) =» 0.00442 «mol»
0.00884 mol of C=C
OR
ratio of linoleic acid : iodine = 1:2
«volume of I2 solution = \(\frac{{0.00884\,{\text{mol}}}}{{0.300\,{\text{mol}}\,{\text{d}}{{\text{m}}^{ - 3}}}}\) =» 0.0295 «dm3» / 29.5 «cm3»
Award [3] for correct final answer.
Any two of:
increases «ratio of» HDL «to LDL» cholesterol
OR
decreases LDL cholesterol «level»
removes plaque from/unblocks arteries
OR
decreases risk of heart disease
decreases risk of stroke «in the brain»
Accept "essential fatty acid".
Do not accept “bad cholesterol” for “LDL cholesterol” OR “good cholesterol” for “HDL cholesterol”.
Do not accept general answers such as “source of energy” OR “forms triglycerides” OR “regulates permeability of cell membranes” etc.
[Max 2 Marks]
