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Chemistry A-level - organic Chem > Alkanes > Flashcards

Alkanes Flashcards

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1
Q

how to name alkanes ?

A

find the longest chain
find the methyl group and its position on the c chain
then state the position of the methyl group and include the name of the carbon chain.

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2
Q

what is meant by an alkane ?

A

alkanes are saturated hydrocarbons with the general formula CnH2n+2

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3
Q

alkanes are hydrocarbons #. what is meant by a hydrocarbon ?

A

a compound that contains only hydrogen and carbon atoms

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4
Q

what is meant by alkanes being saturated ?

A

it means that each carbon is bonded 4 times with the maximum number of hydrogens possible

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5
Q

what are cycloalkanes described as in terms of being saturated ?

A

cycloalkanes are still saturated

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6
Q

what kind of isomer of alkanes are cycloalkanes ?

A

functional group isomers

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7
Q

what is the general formula of cycloalkanes ?

A

CnH2n

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8
Q

where are alkanes found in ?

A

crude oil

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9
Q

what is another word for crude oil ?

A

petroleum

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10
Q

what is crude oil / petroleum ?

A

a mixture of different length hydrocarbons

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11
Q

how can we separate crude oil ?

A

using a fractionating column that uses fractional distillation

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12
Q

why does crude oil need to be separated ?

A

so that it can be separated into smaller more useful alkanes called fractions

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13
Q

1st stage of fractional distillation

A

crude oil is vaporised in a blast furnace to about 350C so that it turns into a gas

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14
Q

2nd stage

A

vaporised crude oil goes into a fractionating column and rises up through the trays. the longest hydrocarbons don’t vaporise and run down to the bottom to form a gooey residue

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15
Q

why do the longest hydrocarbons not vaporise and run to the bottom ?

A

because their boiling points are too high.

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16
Q

what does the column have in terms of temperature ?

A

the column has a temperature gradient. it is cooler at the top and hotter at the bottom

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17
Q

why is it that as the vapour rises, parts of the mixture condense at different temperatures ?

A
  • because there are different chain lengths and hence different boiling points
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18
Q

what happens to the shortest hydrocarbons ? and why ?

A

they won’t condense so will come off as gases at the top of the column
- because they have the lowest boiling points

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19
Q

fraction = gases
number of carbons + uses ?

A

1-4 carbons
-liquified petroleum gas (LPG)
-camping gas

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20
Q

fraction = petrol (gasoline)
number of carbons + uses ?
temp ?

A

5-12 carbons
- petrol
40 C

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21
Q

fraction = naphtha
number of carbons and uses ? temp ?

A

7-14 carbons
-processed to make petrochemicals
110 C

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22
Q

fraction = kerosene (paraffin)
number of carbons and uses ? temp ?

A

11-15 carbons
- jet fuel
- petrochemicals
- central heating fuel
180 C

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23
Q

fraction = gas oil (diesel)
number of carbons + uses ?
temp ?

A

15-19 carbons
- diesel fuel
- central heating fuel
250 C

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24
Q

fraction = mineral oil (lubricating )
number of carbon + uses ?
temp ?

A

20-30 carbons
- lubricating oil
340 C

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25
Q

what are the fractions called in the residue at the bottom of the fractionating column ?

A
  • fuel oil
  • waxes
  • grease
  • bitumen
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26
Q

fraction = fuel oil
number of carbons + uses ?

A

30-40 carbons
- fuel for ships and power stations

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27
Q

fraction = wax , grease
number of carbons + uses ?

A

40-50
-candles
- lubrication

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28
Q

fraction = bitumen
number of carbons + uses ?

A

50 + carbons
- roofing
- road surfacing

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29
Q

what kind of fractions are more demanded ?

A

the lighter fractions of crude oil such as petrol and naphtha

30
Q

which fractions are not as highly demanded ?

A

the heavier fractions of crude oil such as bitumen

31
Q

what is meant by cracking ?

A

breaking long chain alkanes (the heavier fractions ) into shorter more useful hydrocarbons including alkenes

32
Q

how can decane crack
C10H22 ?

A

C10H22 —> C2H4 + C8H18
decane —> ethene + octane

33
Q

what are the 2 products of cracking ?

A

alkane + alkene

34
Q

what are the 2 types of cracking ?

A
  • thermal cracking
  • catalytic cracking
35
Q

conditions for thermal cracking ?

A

high temperature ( up to 1000C)
high pressure ( 70 atm)

36
Q

what are the products of thermal cracking ?

A

mainly alkenes

37
Q

what are the products of thermal cracking used for ?

A

the alkenes produced are used to make polymers ( plastics )
e,g propene is used to make poly(propene)

38
Q

what are he conditions for catalytic cracking ?

A

-high temperature ( 450C)
- slight pressure
- uses a zeolite catalyst (hydrated aluminosilicate )

39
Q

what are the products of catalytic cracking ?

A
  • aromatic hydrocarbons and these are useful in motor fuels
  • branched alkanes
  • cycloalkanes
40
Q

what do aromatic compounds contain ?

A

they contain benzene rings
benzene rings have 6 carbon atoms with 3 double bonds
they are also pretty stable because the electrons are delocalised around the carbon ring

41
Q

what does the zeolite catalyst do to the reaction ?

A

using a zeolite catalyst lowers the temperature and pressure needed for cracking to occur
- this lowers the cost and speeds up the reaction by saving time and therefore saving money

42
Q

what is formed during the complete combustion of alkanes ?

A

carbon dioxide and water

43
Q

why are alkanes good fuels ?

A

alkanes are good fuels as burning just a small amount releases large amounts of energy

44
Q

what are the uses for alkanes ?

A

they are burnt in power stations, central heating systems and used to power vehicles

45
Q

show the complete combustion of butane ?

A

C4H10 + 6.5O2 —-> 4CO2 + 5H2O

46
Q

what is formed during incomplete combustion ?

A

-carbon monoxide and water
or
- carbon soot
and water

47
Q

why is carbon monoxide bad for human health ?

A

carbon monoxide is a colourless, odourless, toxic gas
- it binds to haemoglobin in the blood and prevents oxygen bonding so oxygen cannot be carried around the body

48
Q

how can carbon monoxide be removed ?

A

using a catalytic converter

49
Q

what health issues does carbon soot cause ?

A

breathing problems
makes buildings dirty
clogs up engines
global dimming

50
Q

what does burning fossil fuels lead to ?

A

global warming

51
Q

what does burning fossil fuels produce ?

A

carbon dioxide CO2
- which is a greenhouse gas

52
Q

what is meant by the greenhouse effect ?

A

when greenhouses gases such as CO” in the atmosphere absorb infrared radiation from the sun and emit some of it back into the earth which in turn keeps it warm

53
Q

what do most scientists agree on ?

A

that by increasing the amount of carbon dioxide in the atmosphere we are increasing the global temperatures which leads to global warming

54
Q

where does ozone occur ?

A

at the lowest level of the atmosphere

55
Q

what does the ozone layer contain ?

A
  • sunlight
  • hydrocarbons
  • nitrogen dioxide
56
Q

from where does a great deal of hydrocarbons and nitrogen dioxides come from ?

A

cars and factories

57
Q

how is photochemical smog produced ?

A

when solid carbon particulates and ozone mix

58
Q

what are the health problems caused by smog ?

A

it harms the respiratory system in animals and damages plants

59
Q

what are the problems caused by ground-level ozone ?

A
  • irritates peoples eyes
  • aggravates respiratory problems
  • causes lung damage
60
Q

how are oxides of nitrogen formed ?

A

they are made when nitrogen and oxygen found in the air combine under high pressure and temperature. car engines provide these conditions

61
Q

what machinery helps to reduce the amount of unburnt hydrocarbons and oxides of nitrogen going into the atmosphere ?

A

catalytic converters in the exhaust

62
Q

what is produced when we burn fossil fuels that contain sulfur ?

A

sulfur dioxide

63
Q

why is sulfur dioxide gas so bad ?

A

it gets into the atmosphere and dissolves the moisture and is then converted into sulfuric acid which causes acid rain

64
Q

what does acid rain cause ?

A

acid rain :
- destroys trees and vegetation
- corrodes buildings and statues
- kills fish in lakes

65
Q

how do you remove sulfur dioxide in glue gasses ?

A

through a process called wet scrubbing
- where an alkali is used to neutralise the sulfur dioxide in flue gas

66
Q

what does wet scrubbing involve ?

A

involves dissolving calcium carbonate or oxide in water and spraying it on acidic sulphur dioxide gas
- this therefore forms a harmless salt called calcium sulfite

67
Q

Features of shorter alkanes ?

A
  • lower boiling points
  • more volatile
  • more flammable
  • less viscous
  • less coloured
68
Q

How is the zeolite catalyst arranged ?

A

It is arranged in a honeycomb structure
That allows us to use a small amount of catalyst for a large surface area
Reduces cost

69
Q

What kind of flame do shorter alkanes have ?

A

A clean flame

70
Q

What kind of flame do larger alkanes produce when burnt ?

A

A sootier flame

Chemistry A-level - organic Chem (7 decks)

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