Alkanes ORGANIC

Question 1

Why is crude oil split into fractions?

Answer 1

Not very useful as a mixture
Hydrocarbon fractions are useful, each having different application

Question 2

What does each fraction of crude oil consist of?

Answer 2

Group of hydrocarbons of similar chain lengths

Question 3

Why do hydrocarbons in fractions have similar chain lengths?

Answer 3

Similar boiling points

Question 4

How are fractions in crude oil separated?

Answer 4

Fractional distillation

Question 5

What determines which fraction each hydrocarbon is separated into in fractional distillation?

Answer 5

Size and length of hydrocarbon molecule

Question 6

What are alkanes?

Answer 6

Compounds of carbon and hydrogen containing only single bonds

Question 7

What is the lowest fraction in fractional distillation of crude oil?

Answer 7

Fuel oil

Question 8

What is the second fraction in fractional distillation of crude oil?

Answer 8

Diesel

Question 9

What is the third fraction in fractional distillation of crude oil?

Answer 9

Kerosene

Question 10

What is the highest fraction in fractional distillation of crude oil?

Answer 10

Gasoline

Question 11

Where is fractional distillation carried out?

Answer 11

In a fractionating column

Question 12

What is fractionating column?

Answer 12

Column which is hot at bottom and cool at top

Question 13

Describe the process of the fractional distillation of crude oil.

Answer 13

Crude oil enters fractionating column and heated so vapour rises
Vapours of hydrocarbons with very high boiling points immediately condense into liquid and are tapped off at bottom of column
Vapours of hydrocarbons with low boiling points will rise up column and condense at top to be tapped off

Question 14

What determines height fractions condense at?

Answer 14

Boiling point

Question 15

Where are fractions containing smaller hydrocarbons collected?

Answer 15

Top of fractionating column as gas

Question 16

Where are fractions containing larger hydrocarbons collected?

Answer 16

Lower sections of fractionating column

Question 17

Why is crude oil containing sulfur significant?

Answer 17

Produces sulfur dioxide when burned
One cause of acid rain

Question 18

Is fractional distilllation physical or chemical? Why?

Answer 18

Physical as no bonds broken

Question 19

What two ways can alkanes be produced

Answer 19

Addition reaction of hydrogen to alkene
Cracking of longer alkane chains

Question 20

What is crude oil?

Answer 20

A mixture of hydrocarbonds containing alkanes, cycloalkanes and arenes

Question 21

What are arenes?

Answer 21

Compounds with benzene ring

Question 22

Where does crude oil come from?

Answer 22

Extracted from earth in drilling process and transported to oil refinery

Question 23

Why hydrocarbon fractions are in high demand?

Answer 23

Smaller

Question 24

What happens to excess heavier fractions?

Answer 24

Broken down into smaller, more useful compounds

Question 25

What is cracking?

Answer 25

Process of breaking down complex chemical compounds by heating them

Question 26

How are large hydrocarbons cracked?

Answer 26

Fed into steel chamber and heated to high temperature and then passed over an aluminium oxide catalyst

Question 27

What is missing from steel chamber used to crack hydrocarbons? Why?

Answer 27

Oxygen Prevents combustion of hydrocarbon to water and carbon dioxide

Question 28

What are the two types of cracking?

Answer 28

Thermal cracking Catalytic cracking

Question 29

What is thermal cracking?

Answer 29

Requires high temperatures and high pressure and produces alkanes and lots of alkenes

Question 30

What is catalytic cracking?

Answer 30

Uses lower temperature and slight pressure in presence of catalyst to produce mainly aromatic hydrocarbons

Question 31

Is cracking endothermic or exothermic?

Answer 31

Endothermic

Question 32

What happens when alkanes are burnt in excess oxygen?

Answer 32

Complete combustion All carbon and hydrogen oxidised to carbon dioxide and water

Question 33

What happens when alkanes are burnt in a limited supply of oxygen?

Answer 33

Incomplete combustion Not all carbon fully oxidised Some carbon partially oxidised to carbon monoxide

Question 34

What form does carbon take in incomplete combustion?

Answer 34

Soot

Question 35

What toxic gases are produced by car exhaust?

Answer 35

Carbon monoxide Oxides of nitrogen Volatile organic compounds

Question 36

What is carbon monoxide?

Answer 36

Toxic and odourless gas which can cause dizziness, loss of consciousness and death

Question 37

Why is carbon monoxide toxic?

Answer 37

Binds to haemoglobin which then cannot bind to oxygen or carbon dioxide

Question 38

What effect do nitrogen oxides have?

Answer 38

Dissolve and react in water with oxygen to form nitric acid which is cause of acid rain

Question 39

What are the consequences of acid rain?

Answer 39

Corrosion of buildings, endangers plant and aquatic life

Question 40

What are catalytic converters used for?

Answer 40

Reduce amount of pollutants released in car exhaust fumes

Question 41

What is sulfur scrubbing?

Answer 41

Waster gases are passed into scrubbing chamber which sprays a wet slurry of calcium oxide and calcium carbonate into gases

Question 42

How is peroxyacetyl nitrate (PAN) formed?

Answer 42

Nitrogen oxides react with VOCs

Question 43

What is PAN?

Answer 43

Main pollutant found in photochemical smog

Question 44

How can alkanes undergo free-radical substitution?

Answer 44

Hydrogen atom substituted by halogen

Question 45

What is needed for alkanes to undergo free-radical substitution? Why?

Answer 45

Ultraviolet light Alkanes are very unreactive

Question 46

What are the three steps of free-radical substitution?

Answer 46

Initiation step Propagation step Termination step

Question 47

What is the initiation step of the free-radical substitution of alkanes?

Answer 47

Halogen bond is broken by UV energy Produces two radicals by homolytic fission reaction

Question 48

What is the propagation step of the free-radical substitution of alkanes?

Answer 48

Free radicals are very reactive and attack unreactive alkanes Alkyl free radical produced and attacks another to form halogenalkane and regenerate free radical - repeats

Question 49

What is the termination step of the free-radical substitution of alkanes?

Answer 49

Reaction terminated when two radicals collide and form single unreactive molecule

Question 50

What is meant by homolytic fission reaction?

Answer 50

Where each atom gets on electron from covalent bond