Fats and Oils

   Fats and oils have the same basic structure.

They are made in a condensation reaction when 3 fatty acid groups join with 1 molecule of glycerol. 3 water molecules are produced in each reaction.

Glycerol

  Glycerol is a tri ol – it has 3 hydroxyl groups in its structure. A trihydric alkanol.

It’s chemical name is propan1,2,3 tri ol.

CH I CH 2 I CH 2 2 – OH – OH - OH

Fatty Acids

  Fatty acids contain a carboxyl functional group attached to a long chain.

The chain length can vary – even number of carbon atoms.

 In fats the chains are saturated.

 In oils the chains are unsaturated.

O II HO – C – R ( R = carbon chain, C 4 Usually C 16 – C 18 – C 24 )

The Reaction

I

Glycerol

CH 2 – O H CH I CH 2 2 – O H – O H

Fatty Acids

+ HO OC - R + HO OC – R* + HO OC – R**

The Product

Fat or Oil

CH 2 – OCO I CH 2 – OCO I CH 2 – O II O – C OCO – R – R* + 3 H 2 O – R** Ester link

The New Ester

    The ester formed in the reaction is called a tri glyceride.

Fats and oils are mixtures of triglycerides.

The triglyceride can be broken down in a hydrolysis reaction to form glycerol and the 3 fatty acid molecules.

This is what happens to fat/oils when they are digested.

Uses of Fats and Oils

   Fats and oils are used to produce energy.

They contain twice as much energy as proteins and carbohydrates.

We can compare this in the lab by burning equal masses of foods under a test tube of water and noting the overall T change. The higher the increase in T – the more energy released from the food.

Fats/Oils

   Fats are grouped into: animal( beef, pork etc), vegetable( sunflower, olive etc.) and marine ( cod liver oil etc.) Fats have a higher melting point – the fatty acid chains are saturated and so can be easily stacked together. More Van der Waals’ forces.

Oils have a lower MP – the fatty acid chains are unsaturated making stacking more difficult.

Hardening

   We can harden or saturate oils by adding hydrogen to the fatty acid chain. Hydrogenation Hardened oils are used in margarine.

Soap

   Soaps are made by the hydrolysis of fats and oils using any alkali.

The salt of the alkali is produced as well as glycerol.

O II R – C – O Na +