Date | May 2017 | Marks available | 2 | Reference code | 17M.3.sl.TZ2.8 |
Level | SL | Paper | 3 | Time zone | TZ2 |
Command term | Explain | Question number | 8 | Adapted from | N/A |
Question
Sunflower oil contains stearic, oleic and linoleic fatty acids. The structural formulas of these acids are given in section 34 of the data booklet.
Explain which one of these fatty acids has the highest boiling point.
10.0 g of sunflower oil reacts completely with 123 cm3 of 0.500 moldm–3 iodine solution. Calculate the iodine number of sunflower oil to the nearest whole number.
Markscheme
stearic acid AND chain has no kinks/more regular structure
OR
stearic acid AND it has straight chain
OR
stearic acid AND no C=C/carbon to carbon double bonds
OR
stearic acid AND saturated
OR
stearic acid AND chains pack more closely together
stronger London/dispersion/instantaneous induced dipole-induced dipole forces «between molecules»
Accept “stearic acid AND greater surface area/electron density”.
M2 can only be scored if stearic acid is correctly identified.
Accept “stronger intermolecular/van der Waals’/vdW forces”.
[2 marks]
«n(I2) = 0.123 dm3 x 0.500 moldm–3 =» 0.0615 «mol»
«m(I2) = 0.0615 mol x 253.8 gmol–1 =» 15.6 «g»
«iodine number » = 156
Award [3] for correct final answer.
Iodine number must be a whole number.
Award [2 max] for 78.
[3 marks]