Unsaturated Oils Contain C=C Bonds
oils and fats have long chain molecules with loads of carbon atoms. These carbon atoms either have a single or a double bond.
Unsaturated oils have a double bond between some of their carbon atoms in their carbon chain.
This means if you add them to bromine water it will decolourise the water. This is because the double bond between the carbon atoms pops open and reacts with the bromine.
Monosaturated fats have just on C=C bond. Polyunsaturated fats have more than one.
Hydrogenation just means reacting something with hydrogen. You can do this to unsaturated oils at about 60 degrees in the presence of a nickel catalyst.
The double bonds in the hydrogen pop open and bond with the hydrogen.
Hydrogenated oils have a higher melting point than unsaturated oils so the latter tends to be more of a solid at room temp, while the former are liquids.
Margarine is a partially hydrogenated vegetable oil. If it was done fully it would be too hard to spread!
Hydrogenated oils also tend to last longer before going off – so they are used in processed foods like biscuits.
The downside is partially hydrogenated oils contain lots of trans fats. You don’t need to specifically know about these, but some people suggest they are very bad for you.