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AQA A-Level Organic Chemistry > 3.2 Alkanes > Flashcards

3.2 Alkanes Flashcards

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1
Q

What is the general formula of an alkane?

A

CnH2n+2

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2
Q

What is the functional group of the alkanes?

A

C-C

Carbon carbon single bonds

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3
Q

What are saturated hydrocarbons?

A

Only contains c-c single bonds, contains carbon and hydrogen only

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4
Q

What are some properties of alkanes?

A

Differs by CH2
Insoluble in water
Unreactive
Almost non-polar: Electronegativity difference between carbon and hydrogen is 0.4

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5
Q

What is the significance of different chain lengths?

A

As the carbon chain increases in length the boiling point increases

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6
Q

Why does the boiling points increase with the chain length?

A

There is more surface area for intermolecular forces of attraction therefore the bonds require more energy to overcome

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7
Q

What are intermolecular forces of attraction also called?

A

Van der Waals

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8
Q

What are properties of branched chain alkanes?

A

Lower melting/ boiling point than straight chains

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9
Q

Why do branched alkanes have lower boiling points?

A

They cannot pack together as closely as unbranched chains so the van der waal forces are not as effective

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10
Q

What is used to separate crude oil?

A

Fractional distillation

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11
Q

What is the process of fractional distillation?

A

Crude oil is heated in a furnace
A mixture of liquid and vapour passes into the fractionating column
It is hotter at the bottom and cooler at the top
The vapours pass up the column via a series of trays until they reach one sufficiently cool
The vapour condenses on a tray
Shorter hydrocarbons condense at the top because they have lower boiling points

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12
Q

What is left over in a fractionating column?

A

A thick residue called tar or bitumen

Used for road surfacing

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13
Q

What is the issue with tar?

A

Supply often exceeds demand

It is often processed further to give more valuable products

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14
Q

What is cracking?

A

A process where you break up a large hydrocarbons molecules into smaller more useful molecules

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15
Q

What are the two types of cracking?

A

Catalytic

Thermal

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16
Q

How does catalytic cracking take place?

A

Using the catalyst zeolite
Temp: 500 degrees
Pressure: 1 atmosphere

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17
Q

What is produced in catalytic cracking?

A

High percentage of hydrocarbons between 5 and 10

Branched, aromatic and cycloalkanes

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18
Q

What is zeolite made from?

A

Aluminoscilicates

Lattices of Aluminium, silicon and oxygen

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19
Q

What is special about zeolite?

A

Honeycomb structure creating a large surface area

It has a ionic intermediate - acidic

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20
Q

What is used in catalytic cracking in a laboratory?

A

Mineral wool soaked in light paraffin

Aluminium oxide catalyst

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21
Q

What is produced in catalytic cracking in a laboratory? How can you tell?

A

Mostly gases - chain lengths less than C5

The mixture will decolourise bromine solution (alkene test)

22
Q

How does thermal cracking take place?

A

High temperatures: 450-750 degrees

High pressure: 70 atmospheres

23
Q

What does thermal cracking produce?

A

High proportion of alkenes

24
Q

What happens in thermal cracking?

A

Carbon carbon bonds are broke so each carbon ends up with a single electron i.e free radicals are formed

25
Q

What is fracking?

A

Extracting natural gas trapped within shale rock

26
Q

Why is fracking used?

A

Natural gas supplied by the north sea is decreasing rapidly

Many areas of the UK has natural gas trapped

27
Q

How is gas extracted in fracking?

A

Drill into the shale
Force pressurised water mixed with sand causing the soft shale to break up
Add Hydrochloric acid to help break up the shale
Add methanol to prevent corrosion in the system
This releases trapped gas flowing to the surface

28
Q

What pollutants are produced in combustion?

A 
Carbon dioxide 
Carbon monoxide 
Carbon
Sulfur dioxide
Nitrates of oxides
Carbon particulates
Unburnt hydrocarbons
30
Q

What is produced in complete combustion? Cause?

A

Carbon dioxide CO2

Global warming

31
Q

What is produced in incomplete and very incomplete combustion? Causes?

A

Carbon monoxide CO
Poisonous

Carbon C or soot
Global dimming

32
Q

What is incomplete combustion?

A

A lack of oxygen in the reaction

32
Q

What do carbon particulates cause?

A

Cancer

It can exacerbate asthma

35
Q

Where does sulfur come from if present in combustion equations?

A

It is contained within some parts of crude oil as it is from the sea creatures many years ago

It is an impurity in the crude oil

36
Q

What is produced as a result of sulfur?

A

Sulfuric acid H2SO4

Which is acid rain

37
Q

How is sulfuric acid produced?

A

S + O2 —> SO2
2SO2 + O2 —> 2SO3
SO3 + H2O —> H2SO4

38
Q

How do we prevent sulfuric acid or acid rain being produced?

A

Flue gas desulfurisation

39
Q

What can be used as a neutraliser in flue gas desulfurisation?

A

Calcium oxide

Calcium carbonate

40
Q

Why is there opposition to fracking?

A

Concern about amount of water used
Scared about chemicals polluting the water
Occasional earthquakes
Burning the natural gas itself produces CO2 contributing to global warming

41
Q

What can calcium sulfate be used for?

A

Plasterboard

42
Q

What else can be formed in combustion?

A

Oxides of Nitrogen

43
Q

What are the equations for how smog is formed?

A

N2 + O2 —> NO

N2 + 2O2 —> 2NO2

44
Q

What is the effect of smog?

A

It is bad for the lungs

45
Q

How does N2 and O2 react?

A

Because of the heat in car engines at around 2500 degrees they have enough energy

46
Q

What are used to prevent pollutants?

A

Catalytic converters

47
Q

Where are catalytic converters used? What do they prevent?

A

Cars - just behind the engine

Carbon monoxide, nitrates of oxygen and unburnt hydrocarbons

48
Q

What is the structure of a catalytic converter?

A

Honeycomb structure (large surface area) made from a ceramic material

Coated in platinum, palladium, rhodium or iridium which are catalysts

49
Q

What does the large surface area of the honeycomb structure of the catalytic converter lead to?

A

Little of the expensive metal goes a long way

50
Q

What are some reactions that take place in catalytic converters?

A

Producing CO2 instead of CO

Producing Nitrogen from Nitrates of oxygen

51
Q

What is carbon neutral? Example?

A

Something that produces no overall carbon dioxide emissions

Plants take in CO2
Converted into biodiesel
The CO2 produced is just what was taken in
Therefore no overall change

52
Q

What is the last measure for preventing acid rain?

A

CaO + H2SO4 —> CaSO4 + H2O

53
Q

What kind of reaction is flue gas desulfurisation? What are the reactions?

A

Neutralisation

SO2 + CaO + 1/2 O2 —> CaSO4

SO2 + CaCO3 + 1/2 O2 —> CaSO4 + CO2

AQA A-Level Organic Chemistry (14 decks)

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