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AQA: Chemistry Paper 2 > Alkanes > Flashcards

Alkanes Flashcards

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1
Q

What is the general formula for an alkane?

A

C nH 2n +2

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2
Q

What is rude oil?

A

A mixture of different hydrocarbons

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3
Q

Which chains are in higher demand?

A

Short chains

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4
Q

What type of fractions do you find near the top of the distillation column?

A

Fractions of molecules with lower boiling points and shorter chains

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5
Q

Where is LPG found in the fractionation column?

A

Near the top

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6
Q

Give examples of fractions collected before diesel

[2]:

A
  • Kerosene

- Petrol

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7
Q

What decreases as you go down the fractionation column [2]:

A

Flammability and volatility of chains

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8
Q

What increases as you go down the fractionation column?

A

Viscosity

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9
Q

Where would you be likely to find bitumen on the fractionational distillation column?

A

Near the bottom

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10
Q

What is petroleum?

A

Petroleum is a mixture consisting mainly of alkane hydrocarbons

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11
Q

What is a petroleum fraction?

A

Petroleum fraction: mixture of hydrocarbons with

a similar chain length and boiling point range

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12
Q

Industrial fractional distillation procedure [4]:

A
  • Oil is pre-heated then passed into column.
  • The temperature of column decreases upwards
  • The fractions condense at different heights
  • The separation depends on boiling point which depends on size of molecules
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13
Q

In Industrial fractional distillation the larger the molecule the larger the…

A

Van der waaals forces

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14
Q

Industrial fractional distillation is a process that…

A

involves the splitting of weak van der waals forces

between molecules

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15
Q

Vacuum distillation unit [3]:

A
  • Heavy residues from the fractionating column are distilled again under a vacuum.
  • Lowering the pressure over a liquid will lower its boiling
    point.
  • Allows heavier fractions to be further separated without high temperatures which could break them down
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16
Q

Fractional Distillation in the laboratory [3]:

A
  • Vapours pass up the fractionating column the vapour with the lower boiling point reaches the top of the fractionating column first.
  • The vapours with higher boiling points condense
    back into the flask
  • Only the most volatile vapour passes into the
    condenser
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17
Q

Where should the thermometer be during fractional distillation in the laboratory?

A

thermometer should be at or below the boiling

point of the most volatile substance

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18
Q

What does the condenser do during fractional distillation in the laboratory?

A

The condenser cools the vapours and condenses to

a liquid and is collected

19
Q

What is fractional distillation in the laboratory used for?

A

To separate liquids with different boiling points

20
Q

Cracking [definition]:

A

conversion of large hydrocarbons to smaller hydrocarbon molecules by breakage of C-C bonds

21
Q

Cracking advantages [3]:

A
  • petroleum fractions with shorter carbon chains are in more demand than larger fractions
  • make use of excess larger hydrocarbons
  • The products of cracking are more valuable than the starting materials
22
Q

What does thermal cracking produce? [2]:

A
  • produces mostly alkenes

- sometimes produces hydrogen

23
Q

Conditions for thermal cracking [2]:

A
  • High pressure (7000 kPa)

- High temperature (400°C to 900°C)

24
Q

What is catalytic cracking used for?

A

Making motor fuels

25
Q

What does catalytic cracking produce? [2]:

A
  • branched and cyclic alkanes

- aromatic hydrocarbons

26
Q

Advantages of catalytic cracking [2];

A
  • Branched and cyclic hydrocarbons burn more
    cleanly and are used to give fuels a higher octane
    number
  • Cheaper than thermal cracking because it saves
    energy as lower temperatures and pressures are used
27
Q

Combustion of alkanes [2]:

A
  • Alkanes readily burn in the presence of oxygen
  • This combustion of alkanes is highly
    exothermic
28
Q

What are the harmful products of incomplete combustion [2]:

A
  • CO is toxic

- Carbon (soot) can cause global dimming- reflection of the sun’s light

29
Q

Combustion equation:

A

x + O2 = CO2 + H2O

30
Q

Catalytic converters [2]:

A
  • Converters have a ceramic honeycomb coated with a thin layer of catalyst metals
  • Turn molecules produced in car engines into relatively less harmful ones
31
Q

What are the catalyst metals on catalytic converters?

[3]:

A
  • platinum
  • palladium
  • rhodium
32
Q

Why do catalytic converters have a large honeycomb structure?

A

to give a large surface area

33
Q

Catalytic conversions [2]:

A
  • 2 CO + 2 NO → 2 CO2 + N

- S + O → SO2

34
Q

Why is CO harmful?

A

Toxic

35
Q

Why is CO2 harmful?

A

Greenhouse gas- contributes to global warming

36
Q

Why is NO2 harmful?

A

NO is toxic and can form acidic gas NO2 which is toxic and acidic, forms acid rain

37
Q

Why is Sulphur harmful?

A

Form SO3 in atmosphere which dissolves in water and forms acid rain

38
Q

What happens when alkanes react with bromine/ chlorine under UV light?

A
  • Free radical substitution

- Produces halogenoalkanes

39
Q

Mechanism of greenhouse effect [4]:

A
  • UV wavelength radiation passes through atmosphere to Earth’s surface and heats up surface
  • 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
40
Q

Free radical [definition]:

A

A reactive species which possess an unpaired electron, represented by a dot

41
Q

Initiation:

A

Free radical on products side

42
Q

Propagation:

A

Free radical on products and reactants

43
Q

Termination:

A

Free radical on reactants side

44
Q

What are the conditions for free radical substitution?

[3]:

A
  • UV light
  • Alkene present
  • Halogen present

AQA: Chemistry Paper 2 (7 decks)

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