Fractional Distillation

Question 1

how does crude oil form?

Answer 1

the slow decay of marine animals and plants over millions of years under heat and pressure

Question 2

composition of crude oil?

Answer 2

Mixture of hydrocarbons - mostly alkanes

Question 3

why and how is crude oil separated?

Answer 3

no use in raw form
differences in physical properties (boiling points) allow it to be separated by fractional distillation

Question 4

how does fractional distillation work?

Answer 4

• crude oil vaporised in a furnace
• vaporised crude oil passes into fractionating column (cooler at top than at bottom)
• vapours pass up and cools
• fractions condense at diff temperatures (larger lower down column) - drawn off at different levels in column
• shorter chain hydrocarbons condense nearer to the top as have lower boiling points
• largest don’t vaporise and run to bottom - the thick residue collected at the bottom is called tar- can be used to resurface roads or is further processed to give more valuable products
• molecules with lowest boiling points don’t condense and are drawn off as gases at the top

Question 5

what is a fraction

Answer 5

mixture of hydrocarbons with similar boiling points

Question 6

as carbon chains get longer, what happens the properties of hydrocarbons?

Answer 6

• more viscous
• harder to ignite
• less volatile (the tendency of a substance to vaporise)
• higher boiling points

Question 7

what happens to the residue from primary distillation? why?

Answer 7

separated by further distillation at lower pressure (vacuum distillation) - contain useful substances but would decompose if heated above 350 degrees at atmospheric pressure

Question 8

where does fractional distillation take place?

Answer 8

fractionating tower

Question 9

what type of bonds are broken and reformed in fractional distillation?

Answer 9

van der waals - physical process