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Edexcel A-Level Chemistry > topic 6b- alkanes > Flashcards

topic 6b- alkanes Flashcards

1
Q

6.1. what is the general formula of an alkane?

A

Cn H2n+2
(have single carbon bonds)

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2
Q

6.2. what is a cycloalkane?

A

a saturated hydrocarbon

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3
Q

name 3 ways in which we can obtain alkane fuels?

A
  • fractional distillation
  • cracking
  • reforming
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4
Q

what happens as the molecular mass of alkane’s increases?

A
  1. boiling point INCREASES
  2. viscosity INCREASES
  3. Denser
  4. harder to ignite
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5
Q

why is the boiling point of branched chain alkanes lower than that of unbranched chain alkanes?

A

MORE points of contact= MORE london forces= HIGHER BP

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6
Q

what is crude oil?

A

a mixture of hydrocarbons

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7
Q

describe how crude oil can be separated by fractional distillation

A
  1. the mixture is vapourised (at around 350c) and fed into the fractioning column
  2. vapours rise, cool and condense
  3. products are siphoned off for different uses
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8
Q

why are gases at the top of the fractioning column? and the use of gases?

A

SHORT carbon chain= LOW BP means they rise higher up the column

use= liquefied petroleum gas, camping gas (e.g. methane)

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9
Q

name a use for:
- petrol
- naptha
- kerosene
- gas oil
- mineral oil

A

petrol= cars
naptha= manafacturing of chemicals
kerosene= for aircrafts
gas oil= central heating, diesel
mineral oil= lubricant

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10
Q

why is bitumen at the base of the fractioning column? and its use?

A

LONG carbon chain= HIGH BP
- harder to rise up the fractioning column and condenses easier at base

use= paving roads

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11
Q

what is cracking?

A

compounds collected from the fractioning column that require further breaking down to form smaller, more useful molecules

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12
Q

what is reforming?

A

processing of straight chain hydrocarbons into branched chain alkanes and cyclic hydrocarbons for efficient combustion

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13
Q

what is catalytic cracking?

A

uses zeolite catalyst at a slight pressure ana a high temperature (about 450 degrees)

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14
Q

what is thermal cracking?

A

prouduces a high proportion of alkanes and alkenes
high temperatures of around 1200K and pressures around 7000 kpa

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15
Q

give an example of a cracking equation

A

C10H22 -> C8H18 + C2H4
or C12H26 -> C10H22 + C2H4

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16
Q

give the general equation of complete combustion

A

fuel + oxygen -> CO2 + H2O

17
Q

what is incomplete combustion?

A

some of the atoms in the fuel are not fully oxidised

18
Q

incomplete combustion

give the equation for the formation of carbon

A

C3H8 + 4O2 -> C + 2CO2 + 4H2O

19
Q

INCOMPLETE COMBUSTION

give the equation for the formation of CO

A

C3H8 + 4O2 -> 2CO + CO2 + 4H2O

20
Q

what is knocking?

A

a type of reforming
-alkanes explode to their own accord (likely to occur with straight chain alkanes)

21
Q

name the products formed during the combustion of alkane fuels

A
  • carbon monoxide
  • oxides of nitrogen and sulfur
  • carbon particulates
  • unburned hydrocarbons.
22
Q

describe why carbon monoxide is a bad pollutant

A

toxic gas that can cause death
=prevents transport of O2 to the body

23
Q

drawbacks of nitrogen and sulfur oxides

A
  • can produce acid rain
  • nitrogen monoxide + O2 -> nitrogen dioxide (acidic can dissolve in H2O)
  • ## Acid rain= 2NO2 + H2O -> HNO2 + HNO3SO2 + H2O -> H2SO3 (sulfurous acid)
    as well as sulfur trioxide and sulfuric acid
24
Q

drawbacks of carbon particulates

A
  • formed from incomplete combustion -> seen as smoke or soot
  • can discolour buildings
  • can cause breathing difficulties
25
Q

drawback of unburnt hydrocarbons

A
  • released into air unchanged
  • can be carcinogenic (may be cancerous)
26
Q

6.13. understand how the use of a catalytic converter solves some problems caused by pollutants

A
  • uses a rhodium catalyst to convert harmful products into more stable products (H2O or CO2)
27
Q

what environmental problem does catalytic converters not solve?

A
  • DOES NOT SOLVE CO2
  • potential to lead to global warming
28
Q

equation for catalytic converters and:
-unburnt hydrocarbon
-nitrogen oxide

A
  • CO + O2 -> CO2
  • unburnt hydrocarbon: C8H18 + 12O2 -> 8O2 + 9H2O
  • nitrogen oxide: 2NO + 2CO -> N2 + 2CO2
29
Q

6.14. what is a biofuel
(understand the use of alternative fuels, including biodiesel and alcohols derived
from renewable sources such as plants, in terms of a comparison with non-renewable fossil fuels)

A

fuels made from living matter over a short period of time

30
Q

what is a biodiesel?

A

made by refining renewable fats and oils (e.g. vegetable oil)

31
Q

what is bioethanol?

A

made by the fermentation of sugar from crops

32
Q

what is biogas?

A

produced by the breakdown of organic waste matter

33
Q

define carbon neutral

A

the amount of CO2 released during combustion is the same as absorbed by the life of the organism

34
Q

(land use, yield, manafacture/ transport, carbon neutrality)

compare biofuel and natural gas

A

biofuel=
- land use -a lot of land needed (replaces land that is used to grow food )
- yield - low, gradually increasing
- manafacture/ transport- no exploration or drilling costs, substantial cost in growing, processing and transport
- carbon neutrality- much closer to being carbon neutral

35
Q

6.15. what is a radical?

A

a species with an unpaired electron and is represented in mechanisms by a single dot

36
Q

6.15. how is a radical formed?

A

homolytic fission of a covalent bond and results in the formation of radicals

37
Q

6.16. understand the reactions of alkanes with:
i oxygen in air (combustion)

A

general equation: fuel + oxygen -> CO2 + H2O
- test for limewater: shows that CO2 is present

38
Q

6.16. ii- halogens, in terms of the mechanism of radical substitution through initiation,
propagation and termination steps

A

Overall reaction= CH4 + Cl2 -> CH3Cl + HCl
1. Initiation= always produce radicals
Cl2 -> 2Cl’ (‘=dot)
2. propagation= radicals on both sides of equation
CH4 + Cl’ -> CH3’ + HCl
CH3’ + Cl2 -> CH3Cl + Cl’
3. termination= radicals on reactants side of equation ONLY
Cl’ + CH3’ -> CH3Cl
CH3’ + CH3’ -> CH3CH3
Cl’ + Cl’ -> Cl2

39
Q

6.17. understand the limitations of the use of radical substitution reactions in the synthesis of organic molecules, in terms of further substitution reactions and the formation of a mixture of products

A
  1. LOW yield
  2. a number of products are produced
    (as shown through further substitution reactions)
    CH3Cl + Cl2 -> CH2Cl2 + HCl
    CH2Cl2 + Cl2 -> CHCl3 + HCl trichloromethane is also formed here
    CHCl3 + Cl2 -> CCl4 + HCl
  3. can take place at any point along the carbon chain

Edexcel A-Level Chemistry (13 decks)

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