Question 19N.3.sl.TZ0.9
| Date | November 2019 | Marks available | [Maximum mark: 7] | Reference code | 19N.3.sl.TZ0.9 |
| Level | sl | Paper | 3 | Time zone | TZ0 |
| Command term | Calculate, Explain, Identify, State | Question number | 9 | Adapted from | N/A |
Stearic acid (Mr = 284.47) and oleic acid (Mr = 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]
«one C=C bond»
«1 mole iodine : 1 mole oleic acid»
« =» 89.85 «g of I2» ✔
NOTE: Accept “90 «g of I2»”.
State one impact on health of the increase in LDL cholesterol concentration in blood.
[1]
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"
Explain why stearic acid has a higher melting point than oleic acid.
[2]
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.
State one similarity and one difference in composition between phospholipids and triglycerides.
Similarity:
Difference:
[2]
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”.
Identify a reagent that hydrolyses triglycerides.
[1]
«concentrated» NaOH (aq)/sodium hydroxide
OR
«concentrated» HCl (aq)/hydrochloric acid
OR
enzymes/lipases ✔
NOTE: Accept other strong acids or bases.