B3 Lipids
Question 1
Determine the number of double bonds in linoleic acid, C18H32O2, and
linolenic acid, C18H30O2, and suggest which fatty acid will have a higher
iodine number.
• Refer Data Booklet Table 34
• linoleic has 2 C=C / double bonds and linolenic has 3
C=C / double bonds;
linolenic acid (will have higher iodine value);
Question 2
Explain why it is important to include the fatty acids linoleic
and linolenic acid in a balanced diet.
• Textbook page 567
• essential fatty acids / cannot be synthesized in body;
• lowers LDL cholesterol level / lowers risk of heart disease /
Question 3
(a) The partial equation for the enzyme-catalysed hydrolysis of a
triglyceride is shown below.
Draw the structural formulas of the products A and B.
• A: CH3(CH2)16COOH
• B: CH2OHCHOHCH2OH
Question 3
(b) Deduce whether the fatty acid obtained in part (a) will have a
higher or lower melting point compared to oleic acid,
CH3(CH2)7CH=CH(CH2)7COOH. Outline your reason.
• higher (melting point);
• saturated fatty acids / no C=C bonds;
Reason: close packing, stronger van der Waals’ forces, larger surface
area of contact.
Question 4
Some synthetic hormones are similar in structure to testosterone and are used
as anabolic steroids. Outline one medical and one non-medical use of anabolic
steroids.
• Medical use: recovery from injury/surgery/starvation/illness/disease;
• Non-medical use:
increase in muscle mass / enhances performance/strength in sports and
bodybuilding
Question 5
Triglycerides are one of three types of lipid found in the human body. The
following equation represents the formation of a triglyceride.
X + 3RCOOH  triglyceride + 3Y
(a)
Identify the compounds X and Y.
• X is glycerol/propane-1,2,3-triol/CH2(OH)CH(OH)CH2(OH);
• Y is water/ H2O;
Question 5
(b)
Draw the structural formula of a triglyceride formed from one molecule each
of octanoic acid, lauric acid and stearic acid. The formulas of the acids are shown in
Table 34 of the Data Booklet.
Question 5
(c) Explain whether the triglyceride in part (b) is a solid or a
liquid at room temperature.
• solid as contains (three) saturated/straight fatty acid chains;
• can pack closer together;
• have stronger London/dispersion/van der Waals’ forces between
chains;
Question 5
(d) Identify the type of reaction that occurs during the formation of a
triglyceride.
• esterification / condensation
Question 5
(e) Explain why fats have a higher energy value per mole than
carbohydrates.
• fats contain less oxygen than carbohydrates / are in a less oxidized
state (so more energy is released)
Question 6
Unsaturated fats contain C=C double bonds. The amount of unsaturation
in a fat or oil can be determined by titrating with iodine solution.
(a) Define the term iodine number.
• the number of grams/mass of iodine that add to/react with 100 g
of the fat/lipid/oil;
Question 6
• the number of grams/mass of iodine that add to/react with 100 g
of the fat/lipid/oil;
Question 6
Question 7
Question 8
Hormones play an important role in the body.
(a) Outline the function and production of hormones in the body.
• chemical messenger;
• secreted directly into the blood by endocrine glands;
Question 8
(b) In many communities there are people who use steroids
appropriately, and others who abuse them. Outline one appropriate use
and one abuse of steroids.
• build up depleted muscle due to lack of activity;
assist in recuperation from an illness;
stimulation of bone marrow;
treatment of delayed male puberty;
asthma inhalers;
treatment of female-to-male gender changes;
treatment of inflammation;
Award [1] for any one use.
•
muscle/strength build up for an unfair advantage in sport by athletes;
Award [1] for abuse.
Question 9
Calculate the number of carbon-carbon double bonds in linolenic acid,
C18H30O2, given that 7.7 g of iodine, I2, react with 2.8 g of linolenic
acid.