6.2 Alkanes

Question 1

What is homolytic fission?

Answer 1

It happens when each bonding atom receives one electron from the bonded pair forming two radicals

Question 2

What is heterolytic fission?

Answer 2

When one bonding atom receives both electrons from the bonded pair

Question 3

What are radicals?

Answer 3

Highly reactive, neutral species

Question 4

How is a covalent bond formed from two radicals?

Answer 4

The radicals collide and the electrons are involved the bond formation

Question 5

Describe the process of fractional distillation of crude oil

Answer 5

1. The oil is pre-heated then passed into a column.
2. The fractions condense at different heights and the temperature of column decreases upwards
3. The separation of the fuels depends on boiling point which depends on size of molecules. The larger the molecule the larger the London forces
4. Similar molecules (size, bp, mass) condense together and so are collected at the same fraction
5. Small molecules condense at the top at lower temperatures and big molecules condense at the bottom at higher temperatures.

Question 6

What is the reforming of crude oil?

Answer 6

It is processing of straight-chain hydrocarbons into branched-chain alkanes and cyclic hydrocarbons for efficient combustion.

Question 7

Describe the 𝜎 (sigma) bond in alkane

Answer 7

The sigma bond is a covalent bond which has a direct overlap of the s orbitals of the bonding atoms.

Question 8

What reactions will alkanes undergo?

Answer 8

Combustion and reaction with halogens

Question 9

What type of reaction is combustion?

Answer 9

Oxidation reaction

Question 10

What is the colour of the bunsen burner flame during complete combustion?

Answer 10

Blue flame

Question 11

Which type of hydrocarbon are most likely to undergo incomplete combustion?

Answer 11

Longer chains

Question 12

What are the pollutants formed in the combustion of alkanes?

Answer 12

Carbon monoxide, oxides of nitrogen and sulfur, carbon particulates and unburned hydrocarbons

Question 13

What is the environmental impact of carbon monoxide?

Answer 13

It is toxic/poisonous, binds to haemoglobin

Question 14

What is the environmental impact of soot (carbon)?

Answer 14

Asthma, cancer, global dimming

Question 15

What are the environmental impacts of nitrogen oxides?

Answer 15

NO is toxic and can form smog
NO 2 is toxic and acidic and forms acid rain
Can react with VOCs to make PAN, which is found in photochemical smog.

Question 16

What are the environmental impacts of unbranched hydrocarbons?

Answer 16

They contribute towards formation of smog

Question 17

What is the importance of catalytic converter?

Answer 17

These remove CO, oxides of nitrogen and
unburned hydrocarbons (e.g. octane,
C8H18) from the exhaust gases, turning
them into less toxic products CO 2 , N 2
and H 2 O.

Question 18

What are biofuels?

Answer 18

They are fuels developed from renewable resources.

Question 19

What are the advantages of biofuels?

Answer 19

• Reduces of use of non-renewable fossil fuels
• Use of biodiesel is more carbon-neutral
• Fossil fuels can be used feedstock for organic compounds
• Less large scale pollution

Question 20

What are the disadvantages of biofuels?

Answer 20

• Less food crops may be grown because crops for biofuel would be grown instead
• Reduction of rain forests have to be cut down to provide land
• Shortage of fertile soils

Question 21

How are halogenoalkanes formed from alkanes?

Answer 21

Radical substitution

Question 22

In the presence of what does alkane react with halogens?

Answer 22

UV light

Question 23

What are the three stages of free radical substitution?

Answer 23

Initiation - breaking halogen bond to form free radicals
Propagation - chain part of the reaction where products are formed but free radical remains
Termination - free radicals removed, stable products formed

Question 24

What compounds can be classified as aliphatic?

Answer 24

Alkanes, alkenes and alkynes.

Question 25

What is the mnemonic for naming the first 4 alkanes?

Answer 25

Monkey Eats Peanut Butter
M-eth
E-th
P-rop
B-ut

Question 26

How can alkanes be formed from crude oil?

Answer 26

Fractional distillation and cracking.

Question 27

What are the products of fractional distillation?

Answer 27

Bitumen, fuel oil, diesel, kerosene, gasoline and refinery gases.

Question 28

What is bitumen used for?

Answer 28

Roads and roofs.

Question 29

What is fuel oil used for?

Answer 29

Fuel for ships and power stations.

Question 30

What is diesel used for?

Answer 30

Fuel for vehicles.

Question 31

What is kerosene used for?

Answer 31

Fuel for aircrafts.

Question 32

What is gasoline used for?

Answer 32

Fuel for cars.

Question 33

What are refinery gases used for?

Answer 33

Bottled gas.

Question 34

What types of alkanes are more in demand?

Answer 34

Smaller chain alkanes.

Question 35

What are the types of cracking?

Answer 35

• Thermal cracking: requires high temperature and high pressure. Makes alkanes and and lots of alkenes.
• Catalytic cracking: lower temperature and slight pressure with a catalyst like zeolite or aluminium oxide to make mainly aromatic compounds.

Question 36

What is knocking?

Answer 36

When straight chain alkanes in a car engine explode rather than combust making combustion less efficient.

Question 37

What does reforming use?

Answer 37

A platinum catalyst.

Question 38

What do car exhaust fumes include?

Answer 38

Carbon monoxide, oxides of nitrogen, volatile organic compounds (VOCs).

Question 39

What are catalytic converters?

Answer 39

Precious metals like platinum are coated on a honeycomb metal arrangement.

Question 40

Why are catalytic converters in honeycomb arrangement?

Answer 40

A large surface area.

Question 41

What is a renewable fuel?

Answer 41

A fuel that can be replaced over a short period.

Question 42

What are the 3 main biofuels?

Answer 42

Biodiesel, bioethanol and biogas

Question 43

What are the 3 limitations of free radical substitution?

Answer 43

Impurities, further substitution and substitution of different carbon atoms.