Organic Chemistry - Crude Oil

Question 1

what is crude oil?

Answer 1

a mixture of hydrocarbons

Question 2

how is crude oil separated?

Answer 2

• crude oil is separated by fractional distillation
• crude oil is heated and the oil evaporates.
• the gas goes into the fractional distillation tower. as the gas rises the temperature falls.
• fractions with higher boiling points condense and are collected nearer the bottom of the tower.

Question 3

what are the names and uses of the main fractions from crude oil?

Answer 3

from smallest chain length to largest chain length:
refinery gases - bottled gas
gasoline - fuel for cars
kerosene - fuel for aeroplanes
diesel oil - fuel for lorries
fuel oil - fuel for ships
bitumen - road surfacing

Question 4

what happens to the boiling point of the fractions in crude oil?

Answer 4

the boiling point increases as the number of carbon atoms (chain length) increases

Question 5

what happens to the viscosity of the fractions in crude oil?

Answer 5

the viscosity increases as the number of carbon atoms (chain length) increases

Question 6

what happens to the colour of the fractions in crude oil?

Answer 6

the greater the number of carbon atoms (chain length), the darker in colour that fraction is

Question 7

what happens when fuel is burned?

Answer 7

fuel releases heat energy when burned

Question 8

what is complete combustion of hydrocarbons?

Answer 8

complete combustion happens when there is enough oxygen available, producing carbon dioxide and water

Question 9

what is incomplete combustion of hydrocarbons?

Answer 9

incomplete combustion happens when there isn’t enough oxygen available, with possible products being carbon monoxide, carbon, carbon dioxide and water

Question 10

why is carbon monoxide poisonous?

Answer 10

carbon monoxide is poisonous because it reduces the capacity of the blood to carry oxygen

Question 11

when are nitrogen oxides formed?

Answer 11

when fuels are burned in vehicle engines, high temperatures are reached. at these high temperatures nitrogen and oxygen from the air react to produce nitrogen oxides

Question 12

when is sulfur dioxide formed?

Answer 12

fossil fuels such as coal, gas and oil are derived from crude oil. these fuels are hydrocarbons but also include impurities such as sulfur. when the fuels are burned, sulfur dioxide is produced which can escape into the atmosphere

Question 13

how does sulfur dioxide and oxides of nitrogen oxides contribute to acid rain?

Answer 13

• sulfur dioxide released into the atmosphere from the burning of fossil fuels can react with water and oxygen to make sulfuric acid
• also, if sulfur dioxide in the atmosphere reacts with just water, a weaker acid called sulfurous acid is formed
• in the atmosphere nitrogen oxides can produce nitric acid

Question 14

what is cracking?

Answer 14

cracking involves the thermal decomposition of long-chain alkanes into shorter-chain alkanes and alkenes

Question 15

what conditions are needed for cracking?

Answer 15

temperature: 600C
catalyst: aluminium oxide

Question 16

why is cracking necessary?

Answer 16

• crude oil contains a surplus of long chains
• shorter chain hydrocarbons are in greater demand, e.g. petrol
• cracking also produces alkenes which are used in making polymers and ethanol