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    Hi, if asked a question On FD and the process involved what would the key
    points to mention in a 3/4 mark question, I know the general idea and my textbook doesnst sum it all up well!

    Thanks!
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    This would get you 4/4 Marks - All credit to Alevelchemistry.co.uk

    The different hydrocarbons in crude oil have different boiling points. This is because the chain length varies. The greater the number of carbon atoms in the chain, the longer the chain length. This results in more Van der Waal’s forces acting between the molecules and a greater intermolecular attraction. Thus more energy is needed to separate the molecules and the boiling point is higher. It is the difference in boiling points of the different hydrocarbons in crude oil which is used to separate them from each other.

    The crude oil is passed into a tall tower called a fractionating column. This is very hot near the base but much cooler near the top. When the crude oil is passed into the tower, near the bottom, most of the mixture boils and starts to rise up the tower. As they rise up the tower, they start to cool down and will gradually condense back into liquid form. They are then tapped off. The larger hydrocarbons, with higher boiling points, will condense first and be tapped off near the base of the column. The smaller hydrocarbons, with smaller boiling points, will condense later and be tapped off near the top of the column. Thus the separation is achieved. Not that the process involves breaking intermolecular forces only; the molecules themselves are unaffected by this process.

    This process does not actually separate the crude oil mixture into pure hydrocarbon components, but into mixtures called fractions. Fractions are mixtures of hydrocarbons with similar boiling points. In many cases these fractions can be used directly, but sometimes further separation is required into purer components.
 
 
 
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