Fractional distillation of crude oil (3.3.2.1)

What can alkanes be described as?

Alkanes are saturated hydrocarbons, which means they contain carbon and hydrogen only and contain no double bonds

What is petroleum?

A mixture consisting of mainly alkane hydrocarbons that can be separated by fractional distillation.

What are the physical properties (and trends in them) of alkanes?

Solubility in water

They lack polarity so they are mainly insoluble in water (like dissolves like)

Melting/boiling point

As the chain length increases, the MP/BP increases as they have more surface contact with each other due to a larger surface area, therefore they have greater LDFs so more energy is required to break them

As the branching increases (more alkyl groups), the MP/BP decreases as there are fewer surface points of contact between alkane molecules, thus weaker LDFs therefore less energy is required to overcome these forces

Viscosity

As the chain length increases so does the viscosity

Flammability

As the chain length increases, the flammability decreases

How are the fractions separated in crude oil?

They are separated by fractional distillation which uses a fractionating column that is cool at the top and hot at the bottom.

Before entering the column, the oil is vapourised, this vapour then enters the column and the small molecules rise up further than the large molecules as they have lower BP and condense at the top at the column, whereas the large molecules condense at the bottom.