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Edexcel A-Level Chemistry > Topic 6 - ORGANICS I > Flashcards

Topic 6 - ORGANICS I Flashcards

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1
Q

Features of a homologous series

A
  • Same general formula
  • Show a trend in physical properties
  • Have similar chemical properties
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2
Q

What type of bonds are all single bonds?

A

Sigma bonds

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3
Q

What are the properties of sigma bonds?

A
  • End on overlap
  • Large overlap
  • Directly between nuclei
  • Strong attraction
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4
Q

What are the properties of pi bonds?

A
  • Side on overlap
  • Smaller overlap
  • Not directly between nuclei
  • Significantly weaker
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5
Q

What type of bonds are double bonds?

A

A sigma bond surrounded by 2 pi bonds

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6
Q

What are structural isomers?

A

Molecules with:
- Same molecular formula
- Different structural formula

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7
Q

What are geometric isomers?

A
  • Same molecular formula
  • Different structural formula
  • Restricted rotation about a C=C double bond
  • Different groups on the C atoms
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8
Q

What is a hydrocarbon?

A

Molecules made of hydrogen and carbon atoms only

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9
Q

Definition of an alkane

A

Hydrocarbons with the general formula CnH2n+2

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10
Q

What is the trend of boiling points as alkane size increases?

A

Bp/mp increases

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11
Q

Why does boiling point increase as alkane size increases?

A
  • London forces increase
  • More electrons per molecule
  • More energy required to overcome IMFs
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12
Q

What state is C4H10?

A

Gas

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13
Q

What state is C5H12?

A

Liquid

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14
Q

What is miscibility?

A

The ability of two solutions to combine and form a homogeneous solution

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15
Q

Are alkanes miscible in H2O?

A

No
- CnH2n+2 and H2O cannot form hydrogen bonds

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16
Q

Are alkanes miscible in cyclohexane?

A

Yes
- Both CnH2n+2 and C6H12 only form London forces

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17
Q

Can alkanes bond with other reactants?

A

Not likely
- Alkanes have sigma bonds which are very strong
- Hence low reactivity

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18
Q

What type of reactions can alkanes undertake?

A
  • Combustion reaction
  • Substitution with halogens
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19
Q

Describe the process of obtaining fuel from perch

A
  • Dead matter from the seabed is compressed and heated, producing hydrocarbons
  • Drilling removes the crude oil from the sea
  • Fractional distillation separates the crude oil into fractions
  • Cracking converts long hydrocarbon chains to shorter, more useful chains
  • Reformation converts these chains to shorter, thick branched isomers
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20
Q

What are the main fractions produced in fractional distillation?
Lightest->heaviest

A
  • Refinery gases
  • Gasoline
  • Kerosene
  • Diesel
  • Fuel oil
  • Bitumen
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21
Q

What are the conditions necessary for cracking?

A

~ 650oC
- Catalysts such as aluminium oxide/silica dioxide

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22
Q

Why is reformation useful?

A
  • Isomers are short, thick and branched

Isomers pack less closely together, therefore:
- Weaker London forces
- More efficient combustion

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23
Q

What are the products of complete alkane combustion?

A
  • Highest oxides
  • CO2
  • Exothermic, releases energy

Only when there is sufficient O2

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24
Q

What are the products of incomplete alkane combustion?

A
  • Lower oxides
  • CO2, CO and C

When there is insufficient O2

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25
Q

What are the consequences of pollution by carbon oxides?
CO2 and CO

A

CO2: Greenhouse effect, climate change (long term environmental problem)
CO: Toxic (short term health problem)

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26
Q

What are the consequences of pollution by nitrous oxides?

A
  • Acid rain (Long term environmental problem)
  • Toxic (short term health problem)
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27
Q

How are sulphur oxides produced?

A

When impurities in the oil react in the engine

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28
Q

What are the consequences of pollution by sulphur oxides?
SO2 and SO3

A
  • Acid rain (long term environmental problem)
  • Toxic (short term health problem)
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29
Q

How do catalytic converters reduce the harm caused by pollutants?

A
  • Made of platinum/rhodium
  • Oxidises harmful oxides

Eg.
NO + CO –> 0.5N2 + CO2

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30
Q

What type of reaction is methane + bromine?

A

Alkane (radical) substitution

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31
Q

What is the net reaction of CH4 + Br2 –> ?

A

CH4 + Br2 –> CH3Br + HBr

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32
Q

What are the 3 steps of the alkane substitution mechanism?

A
  • Initiation
  • Propagation
  • Termination
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33
Q

Explain what initiation is in the alkane substitution mechanism?

A

Halogen breaks apart homolytically due to energy from UV light

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34
Q

Explain what is propagation in the alkane substitution mechanism?

A
  • 2 step process in which reactants -> products
  • Catalysed by halogen radical
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35
Q

Explain what is termination in the alkane substitution mechanism?

A

When any two free radicals combine

36
Q

What is the role of UV light in the substitution mechanism?

A
  • Breaks the X-X bond, where X is a halogen
  • It is the only bond that is weak enough for the UV to break
37
Q

What is a radical?

A
  • Species with an unpaired electron
  • Formed by homolytic fission of a covalent bond
38
Q

What is the general formula of alkenes?

A

CnH2n

39
Q

Why are alkenes unsaturated?

A

They contain at least one double bond

40
Q

What occurs in organic reduction?

A
  • Gain of hydrogen
  • Loss of oxygen
41
Q

What occurs in organic oxidation?

A
  • Loss of hydrogen
  • Gain of oxygen
42
Q

What conditions are needed for alkene reduction? (exclude addition of H2)

A
  • 150 degrees celsius
  • Nickel catalyst
43
Q

What is added to an alkene to oxidise it?

A
  • Potassium manganate (VII)/KMnO4
  • Dilute sulphuric acid/H2SO4
44
Q

What symbol represents the oxidising agent potassium manganate (VII)?

A

[O]

45
Q

What is an electrophile?

A

Electron pair acceptors

46
Q

What mechanism/reaction do alkenes undergo?

A

Electrophilic addition

47
Q

Why is a greater amount of the major product produced during an electrophilic addition?

A

The most stable carbocation is produced

48
Q

Which carbocation is the most stable?

A

Tertiary>secondary>primary

49
Q

How is the covalent bond broken in an electrophilic addition reaction?

A

Heterolytic fission

50
Q

What happens when an alkene is passed with steam under pressure with a heated phosphoric acid catalyst?

A
  • Addition reaction
  • OH added
51
Q

Why are heat and pressure required for polymerisation?

A

Heat: breaks pi bond
Pressure: forces molecules closer

52
Q

Advantages of polymers

A
  • Feedstock for cracking
53
Q

Disadvantages of polymers

A
  • If burnt can produce toxic fumes
  • Last many years
  • Can harm wildlife
54
Q

What would the polymer of E- but-2-ene be called?

A

Polybut-2-ene

55
Q

General formula of halogenoalkanes?

A

CnH2n+1X where X is Cl, Br or I

56
Q

What are primary halogenoalkanes?

A

Only one C atom attached to C-X group

57
Q

What are secondary halogenoalkanes?

A

2 C atoms attached to C-X group

58
Q

What are tertiary halogenoalkanes?

A

3 C atoms attached to C-X group

59
Q

What state are most halogenoalkanes?

A

Liquid

60
Q

Are halogenoalkanes miscible in water?

A

No - no hydrogen bonding
- Layers are observed

61
Q

What is a nucleophile?

A

Electron pair donors

62
Q

What mechanism/reactions do halogenoalkanes undergo?

A

Nucleophilic substitution

63
Q

What is added to an alcohol to form a chloroalkane and what is observed?

A

PCl5
Steamy white fumes

64
Q

How is a bromoalkane formed?

A
  • NaBr + 50% H2SO4 -> HBr + NaHSO4
  • HBr is added to the alcohol
65
Q

How is an iodoalkane formed?

A
  • (Red) P + 1.5I2 -> PI3
  • PI3 is added to the alcohol
66
Q

What is formed when KOH(aq) is added to a halogenoalkane?

A

OH- ion forms an alcohol
X- ion removed

67
Q

What is formed when KCN(ethanol) is added to a halogenoalkane?

A

CN- ion forms a nitrile
X- ion removed

68
Q

What is formed when NH3(ethanol) is added to a halogenoalkane?

A

NH3 forms an amine
HX removed

69
Q

When is the SN1 mechanism used?

A

Secondary or tertiary halogenoalkanes

70
Q

When is the SN2 mechanism used?

A

Primary halogenoalkane

71
Q

Why can’t the SN2 mechanism be used for tertiary halogenoalkanes?

A
  • Methyl groups are too bulky for nucleophile to fit
  • Known as steric hindrance
72
Q

Conditions needed for a halogenoalkane elimination?

A

Ethanolic KOH

73
Q

Which halogenoalkane is the most reactive and why?

A

Iodoalkanes
- C-I bonds are longer therefore weaker
- Less energy needed to break them
- They break faster

74
Q

Is SN1 or SN2 faster?

A

SN1
- Tertiary is faster
- Unimolecular, not waiting for a collision

75
Q

What is formed when AgNO3(aq) is added to a halogenoalkane?

A

RX + H2O -> ROH + H+ ion + X-ion
Ag+ + X- -> AgX
- Precipitate of silver halide is observed

76
Q

General formula of alcohols?

A

CnH2n+1OH

77
Q

Products of alcohol combustion and what is observed?

A
  • CO2
  • H2O
  • Blue flame
78
Q

What is added and what happens in an alcohol elimination reaction?

A
  • Warm, concentrated H3PO4 added
  • Alkene formed
  • H2O formed
79
Q

What is added for the oxidation of an alcohol?

A
  • Potassium dichromate (VI)/K2Cr2O7
  • Dilute sulphuric acid/H2SO4
80
Q

Products of the partial oxidation of a primary alcohol?

A

Aldehyde

81
Q

Products of the complete oxidation of a primary alcohol?

A

Carboxylic acid

82
Q

Products of the oxidation of a secondary alcohol?

A

Ketone

83
Q

Why can’t tertiary alcohols be oxidised?

A
  • There is no spare H atom
  • H2O cannot be formed
84
Q

Colour change of the oxidation of primary and secondary alcohols?

A

Orange->green

85
Q

Colour change of the oxidation of tertiary alcohols?

A
  • No change as no oxidation
  • Stays orange

Edexcel A-Level Chemistry (16 decks)

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