| Date | May 2019 | Marks available | 3 | Reference code | 19M.3.sl.TZ1.9 |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | 9 | Adapted from | N/A |
Question
The main fatty acid composition of cocoa butter and coconut oil is detailed below.
The melting points of cocoa butter and coconut oil are 34 °C and 25 °C respectively.
Explain this in terms of their saturated fatty acid composition.
Fats contain triglycerides that are esters of glycerol and fatty acids. Deduce an equation for the acid hydrolysis of the following triglyceride.
The addition of partially hydrogenated cocoa butter to chocolate increases its melting point and the content of trans-fatty acids (trans-fats).
Outline two effects of trans-fatty acids on health.
Markscheme
coconut oil has higher content of lauric/short-chain «saturated» fatty acids
OR
cocoa butter has higher content of stearic/palmitic/longer chain «saturated» fatty acids [✔]
longer chain fatty acids have greater surface area/larger electron cloud [✔]
stronger London/dispersion/instantaneous dipole-induced dipole forces «between triglycerides of longer chain saturated fatty acids» [✔]
Note: Do not accept arguments that relate to the melting points of saturated and unsaturated fats.
correct products [✔]
correctly balanced [✔]
Any two of:
«increased risk of» coronary/heart disease [✔]
«increased risk of» stroke [✔]
«increased risk of» atherosclerosis [✔]
«increased risk of type-2» diabetes [✔]
increase in LDL cholesterol [✔]
decrease in HDL cholesterol [✔]
«increased risk of» obesity [✔]
Examiners report
A classic instance of candidates answering the question they thought (or hoped?) they had been asked rather than the one that was asked. Almost all answers referred to the differing amounts of saturated and unsaturated fatty acids present, totally ignoring the fact that the question clearly stated “their saturated fatty acid composition”, where the relative lengths of the chains was the key point. Nevertheless some who went on to discuss the nature of the intermolecular forces between the chains gained some credit.
A disappointingly small number of candidates gained any marks for deducing the equation for the hydrolysis of the given lipid.
Almost all students were aware of negative health effects of trans-fats, though quite a few lost marks by just stating “cholesterol” without specifying HDL or LDL.
Syllabus sections
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18M.3.sl.TZ1.7c.i:
Fish oil is an excellent dietary source of omega-3 fatty acids. Outline one impact on health of consuming omega-3 fatty acids.
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18M.3.sl.TZ2.6c:
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.
- 17N.3.sl.TZ0.8a.ii: The empirical formula of fructose is CH2O. Suggest why linoleic acid releases more energy per...
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17M.3.sl.TZ2.9b:
Identify the type of reaction which occurs.
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20N.3.sl.TZ0.6a:
Deduce the products of the hydrolysis of a non-substituted phospholipid, where and represent long alkyl chains.
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18M.3.sl.TZ2.6b:
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)
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18M.3.sl.TZ2.6f:
Explain why lipids provide more energy than carbohydrates and proteins.
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18M.3.sl.TZ1.7a.i:
Identify the type of rancidity occurring in saturated lipids and the structural feature that causes it.
- 16N.3.sl.TZ0.8a: Fatty acids react with glycerol to form fats and oils. State the name of the chemical link...
- 18N.3.sl.TZ0.7b.ii: State two functions of lipids in the body.
- 18N.3.sl.TZ0.7c: Outline one effect of increased levels of low-density lipoproteins in the blood.
- 18N.3.sl.TZ0.7a: A phospholipid generally consists of two hydrophobic fatty acids and a hydrophilic...
- 18N.3.hl.TZ0.9b: State two functions of lipids in the body.
- 18N.3.hl.TZ0.9c: Outline one effect of increased levels of low-density lipoproteins in the blood.
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19M.3.hl.TZ1.10b:
Fats contain triglycerides that are esters of glycerol and fatty acids. Deduce an equation for the acid hydrolysis of the following triglyceride.
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19M.3.sl.TZ1.9b:
Fats contain triglycerides that are esters of glycerol and fatty acids. Deduce an equation for the acid hydrolysis of the following triglyceride.
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19M.3.sl.TZ2.7a(i):
Deduce the structural formula of phosphatidylcholine.
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19M.3.sl.TZ2.7e:
Phospholipids are also found in lipoprotein structures.
Describe two effects of increased levels of low-density lipoprotein (LDL) on health.
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19M.3.sl.TZ2.7b:
Lecithin is a major component of cell membranes. Describe the structure of a cell membrane.
- 17N.3.sl.TZ0.8b.i: State the type of reaction occurring during the titration.
- 19N.3.sl.TZ0.9d(i): State one similarity and one difference in composition between phospholipids and...
- 19N.3.sl.TZ0.9c: Explain why stearic acid has a higher melting point than oleic acid.
- 19N.3.hl.TZ0.12c: State one similarity and one difference in composition between phospholipids and...
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19M.3.sl.TZ2.7c:
Predict, giving a reason, the relative energy density of a carbohydrate and a lipid of similar molar mass.
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17M.3.sl.TZ2.9a:
Glycerol is one product of the reaction. Identify the two other organic products.
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19N.3.hl.TZ0.12b:
The chemical change in stored fats causes rancidity characterized by an unpleasant smell or taste.
Compare hydrolytic and oxidative rancidity.
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18M.3.sl.TZ2.6d:
Outline one impact food labelling has had on the consumption of foods containing different types of lipids.
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18N.3.hl.TZ0.9a:
The iodine number is the maximum mass of iodine that reacts with 100 g of an unsaturated compound.
Determine the iodine number of stearidonic acid, C17H27COOH.
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19N.3.hl.TZ0.12a:
The iodine number is the number of grams of iodine which reacts with 100 g of fat. Calculate the iodine number of oleic acid.
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17M.3.sl.TZ1.11a:
List the building blocks of triglycerides and carbohydrates.
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19M.3.hl.TZ2.11a(i):
Deduce the structural formula of phosphatidylcholine.
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17N.3.sl.TZ0.8c:
Outline the importance of linoleic acid for human health.
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19M.3.sl.TZ1.9c:
The addition of partially hydrogenated cocoa butter to chocolate increases its melting point and the content of trans-fatty acids (trans-fats).
Outline two effects of trans-fatty acids on health.
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18N.3.sl.TZ0.7b.i:
The iodine number is the maximum mass of iodine that reacts with 100 g of an unsaturated compound.
Determine the iodine number of stearidonic acid, C17H27COOH.
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19M.3.hl.TZ1.10a:
The melting points of cocoa butter and coconut oil are 34 °C and 25 °C respectively.
Explain this in terms of their saturated fatty acid composition.
- 19N.3.sl.TZ0.9b: State one impact on health of the increase in LDL cholesterol concentration in blood.
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19N.3.sl.TZ0.9d(ii):
Identify a reagent that hydrolyses triglycerides.
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17M.3.sl.TZ1.11b.ii:
Solid fat triglycerides can also clog kitchen sink drains.
Explain how sodium hydroxide unblocks the drain.
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19N.3.sl.TZ0.9a:
The iodine number is the number of grams of iodine which reacts with 100 g of fat. Calculate the iodine number of oleic acid.
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19M.3.hl.TZ2.11d:
Phospholipids are also found in lipoprotein structures.
Describe one effect of increased levels of low-density lipoprotein (LDL) on health.
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19M.3.hl.TZ2.11b:
Lecithin is a major component of cell membranes. Describe the structure of a cell membrane.
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17M.3.sl.TZ2.8b:
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.
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17M.3.sl.TZ1.11b.i:
The drain pipe of a kitchen sink can become clogged by fatty acids, such as linoleic acid, C18H32O2, but not by the trisaccharide, raffinose, C18H32O16, containing the same number of carbon atoms.
Explain why raffinose is far more water soluble than linoleic acid.
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16N.3.sl.TZ0.8b:
The table below shows average figures for the percentage fatty acid composition of some common fats and oils.
(i) Deduce, with a reason, which fat or oil from the table above has the lowest iodine number.
(ii) Deduce, with a reason, which fat or oil from the table above is most likely to become rancid when exposed to the air.
(iii) The P/S index of a fat or oil is the ratio of polyunsaturated fat to saturated fat present. It is sometimes used to compare the relative health benefits of different lipids in the diet. Calculate the P/S index of beef fat and soybean oil.
(iv) Suggest why a P/S index of greater than 1 is considered beneficial to health.
(v) Cotton seed oil and corn oil have similar iodine numbers but the melting point of cotton seed oil is higher than that of corn oil. Suggest an explanation in terms of the structure and bonding in these two oils.
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20N.3.sl.TZ0.6c:
Phospholipids help maintain cellular environments while fatty acid lipids have important roles in energy storage and electrical insulation. Discuss the structural properties of saturated fats needed for these roles.
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17M.3.sl.TZ1.11c:
The amount of proteins, fats and carbohydrates determine the energy content of foods.
Explain why linoleic acid, C18H32O2, is a more efficient energy storage molecule than raffinose, C18H32O16. -
18M.3.sl.TZ1.7a.ii:
State one factor that increases the rate at which saturated lipids become rancid.
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17M.3.sl.TZ2.8a:
Explain which one of these fatty acids has the highest boiling point.
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18M.3.sl.TZ1.7b:
Butter contains varying proportions of oleic, myristic, palmitic and stearic acids. Explain in terms of their structures why stearic acid has a higher melting point than oleic acid, using section 34 of the data booklet.
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20N.3.sl.TZ0.6b(i):
A representation of a phospholipid bilayer cell membrane is shown:
© International Baccalaureate Organization 2020.
Identify the components of the phospholipid labelled A and B.
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17N.3.sl.TZ0.8b.ii:
Calculate the volume of iodine solution used to reach the end-point.
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19M.3.hl.TZ1.10c:
The addition of partially hydrogenated cocoa butter to chocolate increases its melting point and the content of trans-fatty acids (trans-fats).
Outline one effect of trans-fatty acids on health.
