organic chemistry - crude oil

Question 1

what is crude oil?

Answer 1

a mixture of hydrocarbons

Question 2

how does fractional distillation work to separate crude oil

Answer 2

• 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

6 fractions that crude oil is separated into and their uses

Answer 3

• refinery gases - bottled gas
• gasoline - fuel for cars
• kerosene - fuel for planes
• diesel oil - fuel for lorries
• fuel oil - fuel for ships
• bitumen - road surfacing

Question 4

what is a fuel

Answer 4

a substance that, when burned, releases heat energy (exothermic reaction).

Question 5

what is complete combustion

Answer 5

complete combustion happens when there is enough oxygen available, producing carbon dioxide (CO2) and water (H2O)

Question 6

what is incomplete combustion

Answer 6

incomplete combustion happens when there is not enough oxygen available, with possible products being carbon monoxide (CO), carbon (C, soot), carbon dioxide (CO2) and water (H2O)

Question 7

what is carbon monoxide

Answer 7

a gas that is produced by incomplete combustion of fuels

Question 8

why is carbon monoxide poisonous

Answer 8

because it reduces the capacity of the blood to carry oxygen.

Question 9

what happens when fuel is burned in vehicle engines

Answer 9

• high temperatures are reached.
• at these high temperatures nitrogen and oxygen from the air react to produce nitrogen oxides:

nitrogen + oxygen –> nitrogen oxides

In the atmosphere these nitrogen oxides can combine with water to produce nitric acid (HNO3).

Question 10

what happens when impurities in hydrocarbons are combusted

Answer 10

• 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 11

how is acid rain formed

Answer 11

• Acids formed in the atmosphere can fall as acid rain.
• This can be a major problem, killing trees and fish in lakes.
• Sulfur dioxide released into the atmosphere from the burning of fossil fuels can react with water and oxygen to make sulfuric acid (H₂SO₄)
• if sulfur dioxide in the atmosphere reacts with just water, a weaker acid called sulfurous acid (H₂SO₃) is formed
• in car engines the temperature is high enough for the nitrogen in the air to react with oxygen to produce oxides of nitrogen
• In the atmosphere these nitrogen oxides can produce nitric acid (HNO₃).

Question 12

what is cracking

Answer 12

Cracking involves the thermal decomposition of long-chain alkanes into shorter-chain alkanes and alkenes.
- it requires
Temperature: 600 C
Catalyst: aluminium oxide, Al2O3

Question 13

why is cracking necessary

Answer 13

• cracking converts long chain hydrocarbons into short chain hydrocarbons.
• long-chain alkanes are broken down into alkanes and alkenes of shorter length.
• crude oil contains a surplus long chains.
• shorter chain hydrocarbons are in greater demand, e.g. petrol.
• cracking also produces alkenes which are used in making polymers and ethanol.