Oils and fats

Fats and Oils are like hydrocarbons in that they are made up of chains of carbons atoms surrounded by hydrogen atoms. They are not hydrocarbons however, because they also contain oxygen atoms at one end of the chain. Some of the same definitions still do apply:

• fats have no C=C double bonds.
• Vegetable oil molecules with one double bond are called .
• Oil molecules with more than one double bond are called .

We can detect unsaturated molecules because they react with and . Both test chemicals are orange/brown in solution, but form compounds with unsaturated chains. If only saturated molecules are present, then no reaction can take place and the orange colour will remain.

Polyunsaturated oils are far less viscous (more runny) than saturated ones, because double bonds are more than single bonds. This means they don't wrap around each other as much as the more bendy saturated chains. This also means that polyunsaturated oils have a lower melting point - hence they are liquid at room temperature.

The polyunsaturated oils from vegetables are more healthy than the lards and fats from animals. However they are not very good for spreading. To harden them we need to turn some of the chains into ones. This can be done through . This is involves adding hydrogen in a similar way to bromine/iodine test. This removes double bonds raising the melting point of the oil, making it a solid at room temperature.

Hydrogenation

1. The oil is heated to °C
2. Small particles of are added
3. is bubbled through the mixture
4. The nickel opens up the bond and two hydrogen atoms add across the double bond

The nickel acts as a , it speeds up the reaction with out being used up or changed. The nickel is filtered out and the saturated fat is used to make foods such as margarine, chocolate, peanut butter, biscuits and cakes. It turns out that this also slows the products from going off.