1. Fats and oils
Overview
In this section, study the chemistry and structure of edible fats and oils, and learn how the difference in melting points of fats and oils can be explained in terms of structural differences.

2. a) Edible fats and oils Learning intention
Learn about the characteristic properties of fats and oils and study how they are formed by a condensation reaction of glycerol with fatty acids.

3. Fats in the Diet Fats provide more energy per gram than carbohydrates.
Fat molecules are insoluble, and tend to group together and form
a large droplet. This is how fat is stored in the adipose tissue.
We store our extra energy as fat.
The type of fat we eat is important. Animal fats contain important fat
soluble vitamins. Oils, are thought to be healthier than solid fats, as
they are less likely to be deposited inside our arteries.
However, there is an ongoing debate about which fats are better for us.
Polyunsaturated fats are considered to be less potentially harmful to the
heart.

4. Fats and oils Naturally occuring Animal fat Vegetable oil Marine oil
lard
suet
sunflower oil
coconut oil
cod liver oil
whale oil

5. Fats and Oils
50% of your
brain is fat.
Fats and oils are a range of substances all based on glycerol,
propane-1,2,3-triol.
Natural fats and oils are a mixture of triglyceride compounds.
Each OH group can combine chemically with one carboxylic acid
Molecule. The resulting molecules are fats and oils.
They are described as triglycerides.
The hydrocarbon chain in each can be from 4 to 24 C’s long.
The C’s can be single bonded (saturated) or double bonded
(unsaturated).
Glycerol
propane-1,2,3-triol
a trihydric acid

6. Fats and oils
Fats and oils are built from an alcohol with three -O-H groups.
glycerol
Systematic name is propane-1,2,3-triol

7. Fatty Acids Humans fatty acids C17H35COOH CH3(CH2)16COOH
Stearic Acid (suet, animal fat) Saturated
C17H33COOH
CH3(CH2)7CH=CH(CH2)7COOH
Oleic Acid (olive oil) Unsaturated
Octadec-9-enoic acid
Humans fatty acids
Oleic acid
47%
Palmitic acid
24%
Linoleic acid
10%
Stearic acid 8%

8. Fats and oils
The other components of fat molecules are carboxylic acids
such as
Stearic acid
Systematic name is octadecanoic acid

9. Fats and oils Fats and oils are ESTERS of glycerol and
long chain carboxylic acids

10. Fats and oils Removal of water in the condensation reaction gives -
The molecular formula shown above suggests that the fat
molecule is shaped like an E, but the molecule is actually
shaped more like this:

11. Unsaturation in fats and oils
Using a plastic pipette, add five drops of olive oil to 5 cm3 of hexane in a conical flask.
2. Use a burette filled with a dilute solution of bromine water (0.02 mol dm–3) (Harmful and irritant). Read the burette.

12. Unsaturation in fats and oils
3. Run the bromine water slowly into the oil solution. Shake vigorously after each addition. The yellow colour of bromine disappears as bromine reacts with the oil. Continue adding bromine water to produce a permanent yellow colour.
4. Read the burette. Subtract to find the volume of bromine water needed in the titration.
5. Repeat the experiment with: five drops of cooking oil (vegetable) and five drops of cooking oil (animal).

13. Fats and Oils
The degree of saturation in a fat or oil can be determined by the
Iodine Number. (bromine can also be used).
The iodine reacts with the C=C bonds, so the greater the iodine number, the greater the number of double bonds.
Fat
Av Iodine No
Butter 40
Beef Fat 45
Lard 50
Olive Oil 80
Peanut Oil
100
Soya Bean Oil
180
Solid fats – butter, beef fat & lard have low iodine numbers because they are more saturated than the unsaturated oils.
Margarine is made from vegetable oils, butter
from animal fats. One reason why margarine
spreads better!
Omega 3 fatty acids make up a large % of your brain’s fat.

14. In practice both fats and oils are mixtures of esters containing both saturated and unsaturated compounds.
Beef Fat
Olive oil
In general oils have a higher proportion of unsaturated molecules.

15. b) The melting point of fats and oils
Learning intention
Learn how differences in structure of fats and oils lead to differences in strength of intermolecular forces, and therefore to differences in melting points. .

16. Fats and oils Fats are mainly built from carboxylic acids with
C-C single bonds.
Stearic acid in beef fat
Oils have some C=C bonds in the carboxylic acids
from which they are made.
Oleic acid in olive oil

18. Fats and oils Oil Double bonds in oil make the molecule less compact.
Less tightly packed molecules make oils liquid.
Fat
Fat molecules pack together more tightly,
making fats solid at room temperature.

19. Fat
Fat molecules pack together tightly, making fats solid at room temperature.
Double bonds in oil make the molecule less compact.
Oil
Less tightly packed molecules make oils liquid because the bonds between molecules are weaker.

20. Hydrogenation The addition of hydrogen to an unsaturated
oil will ‘harden’ the oil. Increase it’s m.p.
The hydrogen is added across the double bond.
Used with margarine, otherwise margarine
would be a liquid when taken out of the fridge.

21. Structures of Fats and Oils
Hydrolysis of a fat or oil produces a molecule of glycerol (alcohol) for
every 3 carboxylic acid molecules. The carboxylic acids are usually called
long chain fatty acids. Most fats and oils are, in fact, esters of
propane-1,2,3-triol, sometimes called, triesters.
R 1,R 2,R 3 are long carbon chains,
which can be the same or different
Hydrolysis
Glycerol + Fatty Acids
Glycerol
part
Fatty acid part
Triesters.