Paper 2- Alkanes

Question 1

What is a saturated hydrocarbon?

Answer 1

A molecule which contains only carbon and hydrogen and only single bonds

Question 2

Are alkanes polar?

Answer 2

No

Question 3

Why does boiling point increase as chain length increases?

Answer 3

More electrons so larger temporary dipole which creates a larger induced dipole
Stronger Van der Waals

Question 4

Why do branches lower the boiling point?

Answer 4

Smaller surface area
Smaller area of surface contact between molecules
Less Van der Waals

Question 5

What has a bigger effect on boiling point: molecule size or branches?

Answer 5

Molecule size

Question 6

Why are alkanes insoluble in water?

Answer 6

Water molecules held together by hydrogen bonds.
Alkanes only have Van der Waals so can’t overcome attraction between water molecules.

Question 7

What is a fraction in terms of fractional distillation?

Answer 7

A mixture of hydrocarbons with a similar boiling point range

Question 8

What are the four essential features of fractional distillation?

Answer 8

Different length chains have different boiling points
Boiling point depends on Mr
Heated crude oil passes into a fractionating column which is hotter at the top and cooler at the bottom
Longer chains condense at the bottom and shorter chains move further up and condense at their boiling point.

Question 9

Give 3 reasons why cracking is important

Answer 9

There is a greater demand for shorter alkanes
Makes more fuel
Less useful longer chains become more useful shorter chains

Question 10

What are the conditions for thermal cracking?

Answer 10

450-900 celsius
70 atm

Question 11

What are the conditions for catalytic cracking?

Answer 11

450 celsius
Slight pressure
Presence of a zeolite catalyst

Question 12

What does thermal cracking produce?

Answer 12

Mostly alkenes
Alkanes
Sometimes hydrogen

Question 13

What does catalytic cracking produce?

Answer 13

Branched alkanes
Cycloalkanes
Aromatic compounds
Some alkenes

Question 14

What are the products of thermal cracking used for?

Answer 14

Petrol
Alkenes used to produce polymers

Question 15

What are the products of catalytic cracking used for?

Answer 15

Motor fuels

Question 16

What is the general equation for cracking?

Answer 16

Long chain –> Small chain + alkenes (+hydrogen)

Question 17

In what order do you balance a combustion equation?

Answer 17

1) Carbons
2) Hydrogens
3) Oxygens

Question 18

What is complete combustion?

Answer 18

Burning of fuel in a plentiful supply of oxygen

Question 19

What is incomplete combustion?

Answer 19

Burning of fuel in a limited supply of oxygen

Question 20

What is a fuel?

Answer 20

A substance that releases heat when it undergoes combustion

Question 21

What is a solid product of incomplete combustion?

Answer 21

Carbon (soot)

Question 22

How is sulfur dioxide formed?

Answer 22

Burning fuel with sulfur-containing impurities

Question 23

Why is sulfur dioxide harmful?

Answer 23

It causes acid rain

Question 24

How are particulates formed?

Answer 24

Incomplete combustion of hydrocarbons

Question 25

Why are particulates harmful?

Answer 25

Causes respiratory health problems including cancer Global dimming

Question 26

Why are some hydrocarbons released unburnt?

Answer 26

Combustion is not 100% efficient

Question 27

Why are unburnt hydrocarbons harmful?

Answer 27

Contribute to photochemical smog Greenhouse gas

Question 28

How is carbon monoxide formed?

Answer 28

Incomplete combustion of hydrocarbons

Question 29

Why is carbon monoxide harmful?

Answer 29

Is a poisonous gas

Question 30

How is carbon dioxide formed?

Answer 30

Complete combustion of hydrocarbons

Question 31

Why is carbon dioxide harmful?

Answer 31

Greenhouse gas

Question 32

How are nitrogen oxides formed?

Answer 32

Enough energy for nitrogen and oxygen from the air to combine (usually in an engine)

Question 33

Why are nitrogen oxides harmful?

Answer 33

Contribute to acid rain and photochemical smog

Question 34

How is water vapour produced?

Answer 34

Combustion of hydrocarbons

Question 35

Why is water vapour harmful?

Answer 35

Greenhouse gas

Question 36

What are the 3 main greenhouse gases?

Answer 36

Methane Carbon dioxide Water vapour

Question 37

How is sulphur dioxide removed from waste gases in industry?

Answer 37

Flue gas desulfurisation React with calcium oxide

Question 38

Why might flue gas desulfurisation not be 100% efficient?

Answer 38

Not all the sulfur dioxide reacts

Question 39

How does a catalytic converter work?

Answer 39

Uses catalysts such as platinum or rhodium Metals coated onto a honeycomb shaped ceramic material to increase surface area for lower costs

Question 40

What is the equation between carbon monoxide and nitrogen monoxide in a catalytic converter?

Answer 40

2CO + 2NO --> n2 + 2CO2

Question 41

What is the equation between unburnt hydrocarbons and nitrogen monoxide in a catalytic converter?

Answer 41

C8H18 + 25NO --> 8CO2 + 9H2O

Question 42

How does carbon dioxide contribute to global warming? (6)

Answer 42

Incoming EM radiation is absorbed by the Earth Re emitted at IR radiation Some IR radiation is absorbed by C=O bonds And is trapped in the atmosphere Energy is transferred to other molecules By collisions which increase their KE Causing the Earth's temp to increase

Question 43

What is a free radical?

Answer 43

A species that contains an odd number of electrons, with one electron not paired with any other

Question 44

What is the name of the mechanism of chlorination of alkanes?

Answer 44

Free radical substitution

Question 45

What is the essential condition for the chlorination of alkanes?

Answer 45

UV light

Question 46

What condition is needed to form a high yield of tetrachloromethane?

Answer 46

Excess chlorine

Question 47

What condition is needed to form a high yield of chloromethane?

Answer 47

Excess methane

Question 48

How could you separate the products of the chlorination of alkanes?

Answer 48

Fractional distillation as the different products have different boiling points