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AQA A level Chemistry > Alkanes > Flashcards

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

Name the first four alkanes

A

Methane, ethane, propane, butane

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3
Q

Describe and explain the process of fractional distillation

A

Crude oil is heated and fed into a tube
The alkanes are separated via boiling points
So when the vapours reach their boiling points they condense into a liquid and is piped of
Shorter chain alkanes condense nearer to to the top where it is cooler because they have low boiling points
Thick residue collects at base called bitchumen or tar

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4
Q

Why do we crack alkanes

A

Longer chains alkanes aren’t as useful as shorter chains

Shorter chains can be used as fuels and are more useful

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5
Q

Describe the process of thermal cracking

A

Produces a high amount of alkenes

Happens at a high temperature (900 degree C and 450 atmosphères)

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6
Q

What are the disadvantages of thermal cracking

A

It is expensive due to conditions
It is also difficult to determine how short the alkene chain will be
Can be dangerous

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7
Q

Describe catalytic cracking

A

Takes place under (1 to 2 atmospheres and 450 degree C)
In the presence of a zeolite catalyst
Produces motor fuels

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8
Q

What kind of compounds do catalytic cracking form

A

It forms aromatic compounds, hydrocarbons, branched alkanes, motor fuels

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9
Q

What does the term saturated mean

A

Has single bonds only

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10
Q

State the meaning of the term hydrocarbon

A

Contains only carbon and hydrogen atoms

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11
Q

Why should sulfur compounds be removed from fractions before they are used in central heating

Exam Questions

A

Sulphur can react with oxygen to make sulphur dioxide which can causes acidic rain

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12
Q

Explain how oxides of nitrogen are formed

A

the oxygen in the engine reacts with nitrogen in the air under high temperature and pressure

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13
Q

Write an equation to show how nitrogen monoxide in the air is converted into nitrogen dioxide.

A

2NO + O2 -> 2NO2

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14
Q

Nitric acid (HNO3) contributes to acidity in rainwater.

Deduce an equation to show how nitrogen dioxide reacts with oxygen and water to form nitric acid.

A

4NO2 + 02 + 2H20 -> 4HNO3

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15
Q

Write an equation for the cracking of one molecule of dodecane into equal amounts of two different molecules each containing the same number of carbon atoms.

State the empirical formula of the straight-chain alkane that is formed.
Name the catalyst used in this reaction.

A

C12H26 -> C6H12+ C6H14

Empirical formula - C3H7
Catalyst- Zeolite

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16
Q

Name the process used to separate petrol into different fractions

A

Fractional distillation

17
Q

What does carbon dioxide contribute to

A

Global warming

18
Q

What is the use of a catalytic converter

A

It is used to remove exhaust gases before they enter the atmosphere

19
Q

What is the catalyst used in a catalytic converter

A

Platinum or Rhodium

20
Q

Write an equation for the incomplete combustion of C8H18 to form carbon monoxide and water only.
A catalytic converter is used to remove carbon monoxide from the exhaust gases in a car. Identify a catalyst used in the catalytic converter.
Write an equation to show how carbon monoxide is removed in a catalytic converter.
(4)
State why the water produced in the exhaust gases may contribute to global warming

A

Incomplete combustion

C8H18 + 8.5 O2 ~> 8CO + 9H20

Catalyst- Platinum

2CO + 2NO -> 2CO2 + N2

State the reason- water is a greenhouse gas or it absorbs radiation

21
Q

Why do we use flue gas desulphurisation

A

To remove waste products

22
Q

What can unburnt hydrocarbons cause

A

They can cause respiratory problems

23
Q

What is the equation to remove sulphur from fuels

A

Ca0+ SO2 -> CaSO3

24
Q

How can you use CaSO3

A

First add some oxygen to make CaSO4

Then you make something called gypsum

Which is used in plastering

25
Q

Why do nitrogen oxides form

A

Because of the High temperature and spark from the engine

26
Q

Name the greenhouse gases

A

Methane, carbon dioxide, water vapour

27
Q

Describe the mechanism of global warming

A

The Earth radiates out infrared long wavelength radiation.

The C=O Bonds in CO2 absorb infrared radiation so the IR radiation does not escape from the atmosphere.

This energy is transferred to other molecules in the atmosphere by collisions so the atmosphere is warmed.

28
Q

Why is a catalytic converter covered in mesh

A

To increase the surface area

29
Q

What is wet scrubbing

A

Involves dissolving calcium carbonate or oxide in water and spraying on acidic sulphur dioxide gas

AQA A level Chemistry (26 decks)

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