Alkanes

Question 1

Why are alkanes called saturated hydrocarbons?

Answer 1

Because they don’t contain double carbon bonds.

Question 2

How are the alkanes from crude oil removed?

Answer 2

Fractional Distillation

Question 3

How does fractional distillation work?

Answer 3

1. The crude oil is vaporised at high temperatures.
2. The vaporised crude oil goes into the fractionating column and starts to rise.
3. The hydrocarbons with higher boiling points remain at the bottom because they don’t vaporise well.
4. The hydrocarbons with the lower boiling points rise and they cool and condense. They then are collected as a fraction.
   5, Because the alkanes have different boiling points they condense at different temperatures and can be collected at different fractions.

Question 4

What is cracking?

Answer 4

The breaking of long-chain alkanes into smaller hydrocarbons.

Question 5

What are the commercial benefits of cracking?

Answer 5

Smaller hydrocarbons are more in demand so they are more valuable.

Question 6

What are the conditions needed for thermal cracking?

Answer 6

1. High temperatures 400 to 900 degrees
2. High pressures up to 70atm

Question 7

What does thermal cracking produce?

Answer 7

smaller alkanes and alkenes

Question 8

What are the alkenes produced in thermal cracking used for?

Answer 8

They are used to make polymers and ethanol.

Question 9

What conditions are needed for catalytic cracking?

Answer 9

1. zeolite catalyst
2. moderate pressure.
3. temperature of 450 degrees

Question 10

What does catalytic cracking produce?

Answer 10

1. aromatic hydrocarbons
2. branched and cyclic alkanes

Question 11

What is the use for the cyclic hydrocarbons produced in catalytic cracking?

Answer 11

They burn more cleanly so they are used as fuels.

Question 12

Why is catalytic cracking the preferred method of cracking?

Answer 12

It requires a lower temperature which means less energy needs to be used and that saves money.

Question 13

What is produced in the complete combustion of alkanes?

Answer 13

carbon dioxide and water.

Question 14

What is produced in the incomplete combustion of alkanes?

Answer 14

carbon monoxide, sometimes carbon and water

Question 15

What are the environmental consequences of the formation of nitrogen oxides?

Answer 15

Nitrogen oxide is toxic and it can form acidic nitrogen dioxide gas. Nitrogen dioxide is toxic and it can lead to the formation of acid rain.

Question 16

What are the environmental consequences of the formation of carbon monoxide?

Answer 16

It is toxic

Question 17

What are the environmental consequences of the formation of carbon dioxide?

Answer 17

contributes to global warming

Question 18

What are the environmental consequences of the formation of unburnt hydrocarbons?

Answer 18

contribute to the formation of smog in the atmosphere

Question 19

What are the environmental consequences of the formation of soot ( C )?

Answer 19

contribute to global dimming and respiratory problems.

Question 20

How is sulfur dioxide removed from flue gases?

Answer 20

It reacts with carbon oxide to form carbon sulfite which removes the sulfur dioxide from the gases.

Question 21

What is the role of catalytic converters?

Answer 21

They remove carbon monoxide, nitrogen oxides and unburnt hydrocarbons from exhaust gases by turning them into relatively unharmful carbon dioxide, nitrogen and water.

Question 22

How does carbon monoxide contribute to global warming?

Answer 22

They absorb infrared radiation and they emit some of the energy back to the earth which keeps it warm.

Question 23

What is the mechanism to make halogenoalkanes from alkanes?

Answer 23

free radical substitution

Question 24

What is a free radical?

Answer 24

a species that has an unpaired electron.

Question 25

What conditions do you need for free radical substitution?

Answer 25

UV light