2. After completing this lesson you should be able to : Fats and oils are esters formed from the condensation of glycerol (propane-1,2,3- triol) and three carboxylic acid molecules. The carboxylic acids are known as ‘fatty acids’ and are saturated or unsaturated straight-chain carboxylic acids, usually with long chains of carbon atoms. The lower melting points of oils compared to those of fats is related to the higher degree of unsaturation of oil molecules. The low melting points of oils are a result of the effect that the shapes of the molecules have on close packing, hence on the strength of van der Waals’ forces of attraction. Oils can be converted to fats by hydrogenation, an addition reaction with hydrogen. This reduces the degree of unsaturation which increases the melting point. Learners should be familiar with addition reactions. Fats and oils are:  a concentrated source of energy  essential for the transport and storage of fat-soluble vitamins in the body

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. COPY

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

5. Fats and Oils Fats and oils are a range of substances all based on glycerol, propan-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 propan-1,2,3-triol An alcohol with three –OH groups COPY

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

7. Fatty Acids CH 3 (CH 2 ) 16 COOH CH 3 (CH 2 ) 7 CH=CH(CH 2 ) 7 COOH Stearic Acid (suet, animal fat) Saturated Oleic Acid (olive oil) Unsaturated Octadec-9-enoic acid Oleic acid47% Palmitic acid24% Linoleic acid10% Stearic acid8% Humans fatty acids C 17 H 35 COOH C 17 H 33 COOH COPY

8. Fats and oils Stearic acid Systematic name is octadecanoic acid The other components of fat molecules are carboxylic acids such as In fats – the acid always has an even number of carbon atoms. COPY

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

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: COPY

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

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

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

14. 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. COPY

15. http://www.educationscotland.gov.uk/highersci ences/chemistry/animations/oilsfats.asp Yellow margarine song http://www.youtube.com/watch?v=7rzJNy_WZG4 COPY

16. Unsaturation in fats and oils 1.Using a plastic pipette, add five drops of olive oil to 5 cm 3 of hexane in a conical flask. 2. Use a burette filled with a dilute solution of bromine water (0.02 moll –1 ) (Harmful and irritant). Read the burette. Scholar animation available

17. 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). Unsaturation in fats and oils

18. 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. Omega 3 fatty acids make up a large % of your brain’s fat. Solid fats – butter, beef fat & lard have low iodine numbers because they are more saturated than the unsaturated oils. FatAv Iodine No Butter40 Beef Fat45 Lard50 Olive Oil80 Peanut Oil100 Soya Bean Oil 180 Margarine is made from vegetable oils, butter from animal fats. One reason why margarine spreads better! COPY

19. 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. COPY

20. 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 Glycerol part Fatty acid part Hydrolysis Glycerol + Fatty Acids Triesters. COPY