Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

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)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

6.2. what is a cycloalkane?

A

a saturated hydrocarbon

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

name 3 ways in which we can obtain alkane fuels?

A
  • fractional distillation
  • cracking
  • reforming
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what is crude oil?

A

a mixture of hydrocarbons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what is cracking?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is reforming?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what is catalytic cracking?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

give an example of a cracking equation

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
drawback of unburnt hydrocarbons
- released into air *unchanged* - can be carcinogenic (may be cancerous)
26
6.13. understand how the use of a catalytic converter solves some problems caused by pollutants
- uses a **rhodium catalyst** to convert harmful products into more stable products (H2O or CO2)
27
what environmental problem does catalytic converters not solve?
- DOES NOT SOLVE CO2 - potential to lead to global warming
28
equation for catalytic converters and: -unburnt hydrocarbon -nitrogen oxide
- CO + O2 -> CO2 - unburnt hydrocarbon: C8H18 + 12O2 -> 8O2 + 9H2O - nitrogen oxide: 2NO + 2CO -> N2 + 2CO2
29
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)
fuels made from living matter over a short period of time
30
what is a biodiesel?
made by *refining* renewable *fats and oils* (e.g. vegetable oil)
31
what is bioethanol?
made by the *fermentation* of *sugar* from crops
32
what is biogas?
produced by the breakdown of *organic waste matter*
33
define *carbon neutral*
the amount of CO2 released during combustion is the *same* as absorbed by the life of the organism
34
# (land use, yield, manafacture/ transport, carbon neutrality) compare biofuel and natural gas
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
6.15. what is a radical?
a species with an unpaired electron and is represented in mechanisms by a single dot
36
6.15. how is a radical formed?
**homolytic fission** of a covalent bond and results in the formation of radicals
37
6.16. understand the reactions of alkanes with: i oxygen in air (combustion)
general equation: fuel + oxygen -> CO2 + H2O - test for limewater: shows that CO2 is present
38
6.16. ii- halogens, in terms of the mechanism of radical substitution through initiation, propagation and termination steps
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
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
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 (15 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions