Alkanes

Question 1

What are alkanes?

Answer 1

A homologous series of saturated hydrocarbons

Question 2

What is a saturated hydrocarbon?

Answer 2

One which contains only single bonds between the carbon atoms

Question 3

What is crude oil?

Answer 3

A mixture of different hydrocarbons

Question 4

How can the different hydrocarbons in crude oil be separated?

Answer 4

Fractional distillation

Question 5

Why can the different hydrocarbons in crude oil be separated by fractional distillation?

Answer 5

Because they have different boiling points

Question 6

What happens during fractional distillation?

Answer 6

The mixture is vapourised and fed into the fractionating column, the vapours rise and condense at different levels, the fractions are collected

Question 7

What is a fraction?

Answer 7

A group of compounds with similar boiling points that are removed at the same level of a fractionating column

Question 8

What is cracking?

Answer 8

Breaking C-C bonds in alkanes to produce shorter chain alkanes and alkenes

Question 9

Why is cracking used?

Answer 9

Longer chain molecules are less useful than shorter chain molecules but are more abundant

Question 10

What are the conditions for thermal cracking

Answer 10

1200 K and 7000kPa

Question 11

What are the main products of thermal cracking?

Answer 11

Alkanes and alkenes

Question 12

What are the conditions for catalytic cracking?

Answer 12

720 K, atmospheric pressure and a zeolite catalyst

Question 13

What are the main products of catalytic cracking?

Answer 13

Aromatic hydrocarbons and motor fuels

Question 14

Why are alkanes commonly used as fuels?

Answer 14

They combust readily and release large amounts of heat energy

Question 15

What is produced if alkanes undergo complete combustion?

Answer 15

Carbon dioxide and water

Question 16

What is produced if alkanes undergo incomplete combustion?

Answer 16

Carbon monoxide or carbon particles and water

Question 17

What pollutants are produced by internal combustion engines?

Answer 17

Oxides of nitrogen, carbon monoxide, carbon particles, sulfur dioxide and unburnt hydrocarbons

Question 18

Why is carbon dioxide problematic?

Answer 18

It causes global warming

Question 19

Why is carbon monoxide problematic?

Answer 19

It’s toxic

Question 20

Why are carbon particles problematic?

Answer 20

They cause global dimming and breathing difficulties

Question 21

Why are oxides of nitrogen problematic?

Answer 21

They cause acid rain

Question 22

Why is sulfur dioxide problematic?

Answer 22

It causes acid rain

Question 23

Why are unburnt hydrocarbons problematic?

Answer 23

They create smog

Question 24

What pollutants released by internal combustion engines can be removed by a catalytic converter?

Answer 24

Carbon monoxide, oxides of nitrogen and unburnt hydrocarbons

Question 25

What are the catalysts in catalytic converters?

Answer 25

Platinum and rhodium

Question 26

What is the equation for the removal of nitrogen monoxide and carbon monoxide in a catalytic converter?

Answer 26

2NO(g) + 2CO(g) → 2CO2(g) + N2(g)

Question 27

What causes oxides of nitrogen to be produced by internal combustion engines?

Answer 27

The oxidation of atmospheric nitrogen inside car engines

Question 28

What causes sulfur dioxide to be produced by internal combustion engines

Answer 28

Burning fuels that contain sulfur impurities

Question 29

How is sulfur dioxide removed from the atmosphere?

Answer 29

Flue gas desulfurisation

Question 30

What happens during flue gas desulfurisation?

Answer 30

Flue gases are passed through a slurry containing calcium oxide and calcium carbonate which neutralise the sulfur dioxide to form calcium sulphite

Question 31

Why are calcium oxide and calcium carbonate able to neutralise sulfur dioxide?

Answer 31

They are bases

Question 32

What is the equation for the reaction between sulfur dioxide and calcium oxide?

Answer 32

CaO(s) + SO2(g) → CaSO3(s)

Question 33

What is the equation for the reaction between sulfur dioxide and calcium carbonate?

Answer 33

CaCO3(s) + SO2(g) → CaSO3(s) + CO2(g)

Question 34

What happens to the calcium sulphite produced by flue gas desulfurisation and why?

Answer 34

It is oxidised to calcium sulfate because it is more useful

Question 35

When will alkanes react with halogens?

Answer 35

In the presence of UV light

Question 36

What type of reaction is the reaction between an alkane and a halogen to form a halogenoalkane?

Answer 36

Free radical substitution

Question 37

What is a free radical?

Answer 37

An atom or group with an unpaired electron

Question 38

What are the 3 steps in a free radical substitution reaction?

Answer 38

Initiation, propagation, termination

Question 39

What is the initiation step for the reaction between methane and chlorine in UV light?

Answer 39

Cl2 → Cl● + Cl●

Question 40

What are the propagation steps for the reaction between methane and chlorine in UV light?

Answer 40

Cl● + CH4 → HCl + ●CH3 Cl● + CH4 → HCl + ●CH3

Question 41

What are the termination steps for the reaction between methane and chlorine in UV light?

Answer 41

Cl● + Cl● → Cl2 Cl● + ●CH3 → CH3Cl ●CH3 + ●CH3 → C2H6

Question 42

Why is the combination of 2 chlorine radicals not a proper termination step?

Answer 42

Because the UV light would break the chlorine molecule down again

Question 43

What is a catalytic converter?

Answer 43

A device fitted in a car to reduce the amount of emissions from an internal combustion engine

Question 44

What is fractional distillation?

Answer 44

A method of separating a mixture of substances according to their different boiling points