3.3.2.1 Alkanes And Fractional Distillation

Question 1

What are alkanes?

Answer 1

Saturated hydrocarbons

Question 2

What is petroleum?

Answer 2

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

Question 3

What are the types of alkanes

Answer 3

Unbranched (straight)
Branched (chain)
Cyclic

Question 4

What are the physical properties of alkanes

Answer 4

Polarity
Boiling points
Solubility

Question 5

Describe polarity of alkanes

Answer 5

Alkanes are non polar. Thus the only IMF between molecules are weak vdw forces because bigger molecules have large electron clouds

Question 6

Describe the boiling points of alkanes

Answer 6

Increasing IMF is why bpts increase as alkane length increases.Shorter chains are gases at room temp.Alkanes with branched chains have lower mots than alkanes with the same number of carbon atoms this is because they can’t pack as closely as unbranched chains and so the vdw are not as effective

Question 7

Describe the solubility of alkanes

Answer 7

Alkanes are insoluble in water due to water molecules being held together by hydrogen binds which are much stronger than the vdw forces acting between alkanes . However alkanes do much with other relatively non polar liquids

Question 8

How do alkanes react?

Answer 8

They are relatively unreactive
They have strong c-c and c-h bonds
They don’t react with acids bases , oxidising and reducing agents
They do burn and will react with halogens under suitable conditions
They burn in a plentiful supply of oxygen to form co2 and h20 (or in a restricted supply of oxygen CO or carbon

Question 9

How is crude oil separated?

Answer 9

Fractional distillation

Question 10

What is the fractional distillation process?

Answer 10

Crude oil is heated in a furnace

A mixture of liquid and vapour passes into a tower that’s cooler at the top than the bottom

The vapour passes up the tower via a series of trays containing bubble caps until they arrive at a tray that is sufficiently cool (at their bpt) then they condense into a liquid

The shorter the chain hydrocarbons condense in trays nearer the top of the tower where its cooler because they have lower bpts

The thick residue that collects at the base of the tower is called tar or bitumen. It can be used for road surfacing