Introduction to Alkanes and Fractional Distillation

What are alkanes?

Alkanes are saturated hydrocarbons that can either be in chains or cyclic

What is the general formula for chain alkanes?

C_nH_2n+2

What is the general formula for cyclic alkanes?

C_nH_2n

What do alkanes not react with? 

As alkanes are among the most unreactive organic molecules - they don’t react with acids, bases, oxidising or reducing agents 

What does fractional distillation do?

Fractional distillation separates crude oil using the different boiling points of each fraction.

Name the fractions in order from top to bottom

Refinery Gas

Petrol

Naptha

Kerosene

Diesel

Lubricating Oil

Fuel Oil

Residue

What is each fraction used for?

Refinery Gas - Used as fuel

Petrol - Used in cars

Naptha - Used to make chemicals

Kerosene - Jet fuel, paraffin for heating and lighting

Diesel - For diesel engines

Lubricating Oil - Oil for cars and other machines

Fuel Oil - Fuel for ships, factories

Residue - Used to make bitumen, asphalt

What is the boiling point for each of the fractions?

Refinery Gas - 20^o

Petrol - 70^o

Naptha - 120^o

Kerosene - 180^o

Diesel - 260^o

Lubricating Oil - 300^o

Fuel Oil - 350^o

Residue

What is the pattern in boiling points?

The longer the chain the higher the boiling point (increases as you go down)

What is the pattern in viscosity?

As you go down they become more viscous 

What is the pattern in colour? 

As you go down the colour gets darker

In a practical demo state what you would see when hexane (petrol) is lit with a flame

• light in colour

• easy to light

• an orange flame

• not smokey

In a practical demo state what you would see when diesel is lit with a flame

• darker in colour

• not as easy as hexane to light

• a black smoky flame