Fractional Distillation

Question 1

why cant crude oil, being a fossil fuel, be used in itself

Answer 1

because the different hydrocarbons that make it need to be separated first

Question 2

what method of separation is used to separate crude oil into its hydrocarbons

Answer 2

fractional distillation

Question 3

why is crude oil a non renewable resource

Answer 3

because it takes a long time to make and its being use up quicker than its formed

Question 4

what is a name for crude oil, in terms of its non renewability

Answer 4

a finite resource

Question 5

how are hydrocarbons separated through fractional distillation from crude oil

Answer 5

• crude oil is heated until most of it is gas
• gas enters a fractionating column
• column has a temp gradient (hot at bottom cool at top)
• longer hydrocarbons drain out of bottom of column
• shorter hydrocarbons condesne drain out of top of column

Question 6

what is the product of fractional distillation

Answer 6

crude oil mixture separated into different fractions

Question 7

what does each fraction contain when distilled

Answer 7

a mixture of hydrocarbons that all contain similar numbers of carbon atoms, so have similar boiling points

Question 8

why do the longer hydrocarbons drain out of the column at the bottom

Answer 8

because they have high boiling points, and because the fractionating column gets cooler as you go up, the hydrocarbons with higher boiling points quickly condense to liquids at the bottom and drain from there

Question 9

why do the shorter hydrocarbons drain out of the column at the top

Answer 9

because they have low boiling points, and because the fractionating column gets cooler as you go up, the hydrocarbons with shorter boiling points evaporate, rise and condense at the top where it’s cooler

Question 10

what is the approximate number of carbon atoms that condense at the top of the column

Answer 10

3

Question 11

what is the approximate number of carbon atoms that condense at the bottom of the column

Answer 11

40

Question 12

what is fractional distillation used for in a lab

Answer 12

to separate a mixture of liquids with similar boiling points

Question 13

explain how fractional distillation is used in a lab

Answer 13

• mixture in flask with fractionating column on top then heat
• evaporate at different temps as different liquids have different boiling points
• liquid with lowest boiling point evaporates first
• when temp on thermometer matches boiling point, it reaches top
• cools and condenses at the top into a container
• when first liquid is collected, temp is raised until the next one reaches the top

Question 14

why is the lab method of fractional distillation effective

Answer 14

although liquids with higher boiling points might start evaporating, the column is cooler at the top so they only get part of the way before condensing and running back down the flask

Question 15

what is the fractionating column used in the lab for fractional distillation

Answer 15

a rod filled with smaller glass rods