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Aqa A Level Chemistry > Alkanes and Halogenalkanes lol > Flashcards

Alkanes and Halogenalkanes lol Flashcards

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1
Q

What do alkenes contain?

A

Only hydrogen and carbon do hydrocarbons

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2
Q

How many bonds does every carbon atom in an alkane make?

A

Four single bonds with other atoms so impossible for carbon to make more than four bonds so alkenes are saturated (only contain single bonds)

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3
Q

Alkanes first four

A

Methane
Ethane
Propane
Butane

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4
Q

What else can you get like alkanes?

A

Cycloalkanes but have different general formula

CnH2n assuming only one ring but still saturated

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5
Q

Petroleum what is it?

A

Crude oil
Mixture of hydrocarbons (mainly alkanes ranging from small alkanes like pentane to massive alkanes of more than 50 carbons.

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6
Q

Is crude oil useful?

A

Not as it is it needs to undergo fractional distillation

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7
Q

Fractional distillation step 1

A

1) first the crude oil is vaporised at about 350 degrees

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8
Q

Fractional distillation step 2

A

Vaporised crude oil goes into a fractional column and rises up through the trays. The largest hydrocarbons don’t vaporise at all, because their boiling points are too high- they just run to the bottom and form a gooey residue

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9
Q

Fractional distillation step 3

A

As crude oil vapour goes up the fractionating column it gets cooler because alkane molecules have different chain lengths they have different boiling points so each fraction condenses at a different temperature. The fractions are drawn off at different levels in the column. They’re drawn off as gases at the top of the column

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10
Q

Gases

A

1-4 carbons

Liquefied petroleum gas (LPG) camping gas

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11
Q

40 degrees

A

Petrol
5-12 carbons
Petrol

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12
Q

110 degrees

A

Naphtha
7-14 carbons
Processed to make petrochemicals

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13
Q

180 degrees

A

Kerosene (paraffin)
11-15 carbons
Jet fuels. Petrochemicals, central heating

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14
Q

250 degrees

A

Gas oil (diesel)
15-19 carbons
Diesel fuel, central heating fuel

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15
Q

340 degrees

A

Mineral oil (lubricating)
20-30 carbons
Lubricating oil

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16
Q

Residue

A

Fuel oil, 30-40 carbons, ships, power stations
wax, grease, 40-50 candles lubrication
bitumen
50+ roofing, road surfacing

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17
Q

What’s most in demand from crude oil?

A

Lighter fractions of crude oil like petrol and naphtha
Heavier stuff like bitumen
So more expensive to get stuff in demand

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18
Q

How is this demand met?

A

Less popular heavier fractions are cracked. Cracking is breaking long-carbon chain alkanes into smaller hydrocarbons (including alkenes) involved breaking c-c bonds

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19
Q

Can you choose a certain length to crack to?

A

No where the chain breaks is random so you’ll get a different mixture of products everything you crack a hydrocarbon

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20
Q

General formula for alkane a?

A

CnH2n+2

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21
Q

What do alkenes contain?

A

Only hydrogen and carbon do hydrocarbons

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22
Q

How many bonds does every carbon atom in an alkane make?

A

Four single bonds with other atoms so impossible for carbon to make more than four bonds so alkenes are saturated (only contain single bonds)

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23
Q

Alkanes first four

A

Methane
Ethane
Propane
Butane

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24
Q

What else can you get like alkanes?

A

Cycloalkanes but have different general formula

CnH2n assuming only one ring but still saturated

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25
Q

Petroleum what is it?

A

Crude oil
Mixture of hydrocarbons (mainly alkanes ranging from small alkanes like pentane to massive alkanes of more than 50 carbons.

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26
Q

Is crude oil useful?

A

Not as it is it needs to undergo fractional distillation

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27
Q

Fractional distillation step 1

A

1) first the crude oil is vaporised at about 350 degrees

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28
Q

Fractional distillation step 2

A

Vaporised crude oil goes into a fractional column and rises up through the trays. The largest hydrocarbons don’t vaporise at all, because their boiling points are too high- they just run to the bottom and form a gooey residue

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29
Q

Fractional distillation step 3

A

As crude oil vapour goes up the fractionating column it gets cooler because alkane molecules have different chain lengths they have different boiling points so each fraction condenses at a different temperature. The fractions are drawn off at different levels in the column. They’re drawn off as gases at the top of the column

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30
Q

Gases

A

1-4 carbons

Liquefied petroleum gas (LPG) camping gas

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31
Q

40 degrees

A

Petrol
5-12 carbons
Petrol

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32
Q

110 degrees

A

Naphtha
7-14 carbons
Processed to make petrochemicals

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33
Q

180 degrees

A

Kerosene (paraffin)
11-15 carbons
Jet fuels. Petrochemicals, central heating

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34
Q

250 degrees

A

Gas oil (diesel)
15-19 carbons
Diesel fuel, central heating fuel

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35
Q

340 degrees

A

Mineral oil (lubricating)
20-30 carbons
Lubricating oil

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36
Q

Residue

A

Fuel oil, 30-40 carbons, ships, power stations
wax, grease, 40-50 candles lubrication
bitumen
50+ roofing, road surfacing

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37
Q

What’s most in demand from crude oil?

A

Lighter fractions of crude oil like petrol and naphtha
Heavier stuff like bitumen
So more expensive to get stuff in demand

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38
Q

How is this demand met?

A

Less popular heavier fractions are cracked. Cracking is breaking long-carbon chain alkanes into smaller hydrocarbons (including alkenes) involved breaking c-c bonds

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39
Q

Can you choose a certain length to crack to?

A

No where the chain breaks is random so you’ll get a different mixture of products everything you crack a hydrocarbon

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40
Q

General formula for alkane a?

A

CnH2n+2

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41
Q

Two types of cracking?

A

Thermal cracking

Catalyst cracking

42
Q

What conditions does thermal cracking need?

A 
A high temperature( up to 1000oC)
High pressure (up to 70 atomspheres)
43
Q

What does thermal cracking produce?

A

A lot of alkenes
Alkenes are used to make heaps of valuable products like polymers (plastic). A good example is poly(ethene) which is made from ethene.

44
Q

What conditions does catalytic cracking need?

A

A zeolite catalyst (hydrated aluminosilicate)
Slight pressure
High pressure (about 450oC)

45
Q

What does catalytic cracking produce?

A

Aromatic hydrocarbons and motor fuels

46
Q

Describe aromatic compounds

A

Contain benzene rings
Benzene rings have six carbons with three double bonds
Pretty stable because electrons are delocalised around the carbon ring

47
Q

Why is catalytic cracking cheaper than thermal cracking?

A

Using a catalyst cuts costs because the reaction can be done at a low pressure and a lower temperature
The catalyst also speeds up the reaction saving time and time is money

48
Q

What happens if you burn (oxidise) alkanes and other hydrocarbons with plenty of oxygen?

A

Carbon dioxide and water
Combustion reaction
Complete combustion

49
Q

What do alkanes make?

A

Great fuels

Burning just a small amount releases a humongous amount of energy

50
Q

Where are alkanes used?

A

Burnt in power stations, central heating systems and to power a car

51
Q

Downside of alkanes?

A

Produce a lot of pollutants

52
Q

What happens if there’s not enough oxygen around?

A

Hydrocarbons combust incompletely to produce either carbon monoxide or carbon particles

53
Q

When a hydrocarbon undergoes incomplete combustion?

A

You get carbon monoxide gas instead or as well as carbon dioxide

54
Q

Why is carbon monoxide bad news?

A

It’s poisonous
Binds to the same sites on haemoglobin molecules in red blood cells as oxygen molecules so oxides can’t be carried around the body.
Luckily, carbon monoxide can be removed from exhaust gases by catalytic converters on cars

55
Q

Soot can be formed by?

A

Incomplete combustion

56
Q

Why is soot bad news?

A

Thought to cause breathing problems

Can build up in engines meaning they don’t work properly

57
Q

Burning fossil girls produces what?

A

Carbon dioxide

58
Q

What is carbon dioxide?

A

Greenhouse gas

59
Q

Greenhouse effect?

A

Greenhouse gases in our atomspheres are really good at absorbed infrared energy (heat). Emit some of the energy they absorb back towards the Earth keeping it warm.

60
Q

What do most scientists agree?

A

Increasing the amount of carbon dioxide in our atomsphere we are making the Earth warmer
It’s called global warming
Just learn this rubbish

61
Q

What don’t engines do?

A

Burn all fuel molecules some will come out as unburnt hydrocarbons

62
Q

When are oxides of nitrogen (NOx) produced?

A

When high pressure and temperature in a car engine cause the nitrogen and oxygen atoms from the air to react together

63
Q

When do hydrocarbons and nitrogen oxides react together?

A

In the presence of sunlight to form ground-level ozone (O3) which is a major component of smog.

64
Q

What does ground-level ozone do?

A

Irritate people’s eyes
Aggravates respiratory problems
Causes lung damage (ozone isn’t nice stuff unless it’s high up in the atomsphere as part of the doubt layer)

65
Q

What do catalyst converters do?

A

Remove unburnt hydrocarbons and oxides of nitrogen from the exhaust

66
Q

What do some fossil fuels contain?

A

Sulfur

When burnt sulfur reacts to form sulfur dioxide gas (SO2)

67
Q

Sulfur dioxide is it good?

A

NO
If it gets into the atomsphere it dissolves into the moisture and is converted into sulfuric acid which causes acid rain.

68
Q

What else causes acid rain?

A

When nitrogen oxides escape into the atomsphere- nitric acid is produced

69
Q

Why does acid rain matter?

A

Destroys trees and vegetation
Corroding building and statues
Kills fish in lakes

70
Q

Sulfur dioxide can be removed how from power stations flue gases before it gets into the atomsphere?

A

Powdered calcium carbonate (limestone) or calcium oxide mixed with water to make an alkaline slurry. When flue gases mix with alkaline slurry, the acidic sulfur dioxide gas reacts with calcium compounds to form harmless calcium sulfate

71
Q

What’s a free radical?

A

A particle with an unpaired electron
Unpaired electron makes them very reactive
Represented by •

72
Q

When do free radicals form?

A

When a covalent bond splits equally giving one electron to each atom

73
Q

When do halogen react with alkanes?

A

In photochemical reactions-reactions started by UV light

Hydrogen atom substituted by chlorine or bromine. Free radical substitution reaction

74
Q

Chlorine and methane goes to?

A

UV

CH4+Cl2=> CH3Cl+HCl

75
Q

Three stages of free-radical substitution reaction?

A

Initiation reaction
Propagation reaction
Termination

76
Q

Initation reaction

A

Free radicals produced
Sunlight provides enough energy to break Cl-Cl bond (photodissociation)
Cl2=UV=> 2Cl•
Bond splits equally and each atom gets to keep one electron. Atom becomes highly reactive free radical Cl• because of unpaired electron

77
Q

Proposition reaction

A

Free radical used up and created in chain reaction
Cl• +CH3-> CH3• +HCl
CH3• +Cl2=> CH3+Cl•
New Cl• can attack another CH4 molecule and do on until all Cl2 or CH4 molecules are used up

78
Q

Termination reaction

A

Free radicals mopped up
If two free radicals join together they form a stable molecule
The two unpaired electrons form covalent bond
Heaps of possible termination reactions
Cl• +CH3• => CH3Cl
CH3• +CH3•=> C2H6

79
Q

What happens after termination

A

If chlorine in excess Cl• free radicals will start attacking chloromethane producing CH2Cl2 CHCl3 CCl4
But if methane in excess product will mostly be chloromethane

80
Q

What a are CFC’s

A

Chlorofluorocarbons

Halogenalkane molecules where all of the hydrogen atoms have been replaced by chlorine and fluorine

81
Q

What does ozone in the upper atomsphere do?

A

Acts as a chemical sunscreen
Absorbs lots of UV radiation from the Sun stopping it from reaching us
UV radiation can cause sunburn or even skin cancer

82
Q

How is ozone formed naturally?

A

When an oxygen molecule is broken down into two free radicals by UV radiation
Free radicals attack other oxygen molecules forming ozone
O2=UV=> O•+O•
O2+O•=>O3

83
Q

How are CFC’s causing holes in the ozone?

A

Chlorine free radicals are formed in the upper atmosphere when C-Cl bonds in CFCs are broken down by UV radiation
CCl3F=UV=> CCl2F+Cl•
Free radicals are catalysts
React with ozone to form intermediate ClO• and an oxygen molecule
Cl• +O3=> O2+ ClO•
ClO•+O3=> 2O2+Cl•

84
Q

Overall equation

A

2O3=> 3O2

Cl• is the catalyst

85
Q

Chlorine free radical regenerated?

A

Can go straight on to attack another ozone molecule so only takes one chlorine free radical to destroy loads of ozone molecules

86
Q

CFC’s were used because?

A

Pretty unreactive, non-flammable and non-toxic

Used to be used as coolant gas in fridges as solvents and as propellants in aerosols

87
Q

Why did they stop using them?

A

1970’s research by several different scientific groups demonstrated that CFCs were causing damage to the ozone. The advantages of CFCs couldn’t outright the environmental problems they were causing so they were banned.

88
Q

How come we still can have fridges and stuff now CFCs are banned?

A

Chemists have developed safer alternatives to CFCs which contain no chlorine such as HFC hydrofluorocarbons and hydrocarbons

89
Q

What’s a halogenoalkane?

A

An alkane with at least one halogen atom in place of a hydrogen atom

90
Q

Halogens are much more?

A

Electronegative than carbon so carbon-halogen bonds are polar

91
Q

δ+ charge on the carbon does what?

A

Makes it prone to attacks from nucleophiles

92
Q

What’s a nucleophile?

A

An electron-pair donor
Donates an electron pair to somewhere without electrons
OH-, CN-, NH3 are all nucleophiles that can react with halogenoalkanes

93
Q

What can a nucleophile react with?

A

With a polar molecule by kicking out the functional group and taking its place (nucleophilic substitution reaction go learn it)

94
Q

The carbon- halogen strength decides what?

A

Reactivity for any reaction to occur the carbon-halogen bond needs to break

95
Q

What bond is the strongest?

A

C-F
It has the highest bond enthalpy
So fluoroslksnrd undergo nucleophilic substitution reactions slower the other halogenoalkanes

96
Q

Lowest bond enthalpy?

A

C-I bond
So easier to break
Iodoalkanes substituted quicker

97
Q

Explain elimination reaction theory

A

Warm halogenoalkane with HO- ions dissolved in ethanol instead of water an elimination reaction happens and you end up with an alkene
Anhydrous
Under reflux or you’ll lose volatile stuff
Learn the mechanism

98
Q

What happens when halogenalkanes react with hydroxide?

A

Either they will undergo nucleophilic substitution or elimination depending on the conditions and are said to be competing

99
Q

What conditions favour nucleophilic substitution?

A

OH-/ water
Reflux
Aqueous conditions
OH- acts as a nucleophile

100
Q

What conditions favour elimination?

A

Anhydrous conditions
OH- acts as a base
OH-/ ethanol
Reflux

101
Q

What would happen if you used a mixture of water and ethanol as a solvent?

A

Both reactions will happen and you’ll get a mixture of two products

Aqa A Level Chemistry (12 decks)

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