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7.02 A-Level Organic KW > 3.2 Alkanes > Flashcards

3.2 Alkanes Flashcards

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
What is fracking?
Extracting natural gas trapped within shale rock
26
Why is fracking used?
Natural gas supplied by the north sea is decreasing rapidly | Many areas of the UK has natural gas trapped
27
How is gas extracted in fracking?
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
What pollutants are produced in combustion?
``` Carbon dioxide Carbon monoxide Carbon Sulfur dioxide Nitrates of oxides Carbon particulates Unburnt hydrocarbons ```
30
What is produced in complete combustion? Cause?
Carbon dioxide CO2 Global warming
31
What is produced in incomplete and very incomplete combustion? Causes?
Carbon monoxide CO Poisonous Carbon C or soot Global dimming
32
What do carbon particulates cause?
Cancer | It can exacerbate asthma
33
What is incomplete combustion?
A lack of oxygen in the reaction
35
Where does sulfur come from if present in combustion equations?
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
What is produced as a result of sulfur?
Sulfuric acid H2SO4 Which is acid rain
37
How is sulfuric acid produced?
S + O2 —> SO2 2SO2 + O2 —> 2SO3 SO3 + H2O —> H2SO4
38
How do we prevent sulfuric acid or acid rain being produced?
Flue gas desulfurisation
39
What can be used as a neutraliser in flue gas desulfurisation?
Calcium oxide | Calcium carbonate
40
Why is there opposition to fracking?
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
What can calcium sulfate be used for?
Plasterboard
42
What else can be formed in combustion?
Oxides of Nitrogen
43
What are the equations for how smog is formed?
N2 + O2 —> NO | N2 + 2O2 —> 2NO2
44
What is the effect of smog?
It is bad for the lungs
45
How does N2 and O2 react?
Because of the heat in car engines at around 2500 degrees they have enough energy
46
What are used to prevent pollutants?
Catalytic converters
47
Where are catalytic converters used? What do they prevent?
Cars - just behind the engine Carbon monoxide, nitrates of oxygen and unburnt hydrocarbons
48
What is the structure of a catalytic converter?
Honeycomb structure (large surface area) made from a ceramic material Coated in platinum, palladium, rhodium or iridium which are catalysts
49
What does the large surface area of the honeycomb structure of the catalytic converter lead to?
Little of the expensive metal goes a long way
50
What are some reactions that take place in catalytic converters?
Producing CO2 instead of CO Producing Nitrogen from Nitrates of oxygen
51
What is carbon neutral? Example?
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
What is the last measure for preventing acid rain?
CaO + H2SO4 —> CaSO4 + H2O
53
What kind of reaction is flue gas desulfurisation? What are the reactions?
Neutralisation SO2 + CaO + 1/2 O2 —> CaSO4 SO2 + CaCO3 + 1/2 O2 —> CaSO4 + CO2

7.02 A-Level Organic KW (14 decks)

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