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AQA A Level Organic Chemistry > 5. Alcohols > Flashcards

5. Alcohols Flashcards

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1
Q

General formula for alcohols?

A

CnH₂n₊₁OH

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2
Q

Are alcohols saturated or unsaturated?

A

Saturated

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3
Q

What is the functional group in alcohols?

A

-OH

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4
Q

What can the H in the O-H bond in alcohols do, in terms of bonding?

A

It can hydrogen bond with other alcohol molecules and with water

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5
Q

What can alcohols hydrogen bond to?

A

Other alcohol molecules and water

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6
Q

Why can alcohols form hydrogen bonds?

A

The H in the O-H bond

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7
Q

Why do alcohols have relatively high boiling points?

A

They can hydrogen bond

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8
Q

Why are many alcohols soluble in water?

A

They can hydrogen bond

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9
Q

What is it called when a molecule has a double bond and an O-H bond?

A

An alkenol

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10
Q

How can ethanol be manufactured industrially?

A
  • hydration of alkenes

* fermentation to produce ethanol

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11
Q

What decides which method for ethanol to be manufactured?

A

Depends on desired purity of ethanol and the availability of the different raw materials in the country where is it made

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12
Q

What reaction takes place when alcohols are produced from alkenes?

A

Addition

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13
Q

Why does an addition reaction need to take place when alcohols are produced from alkenes?

A

To get rid of the double bond

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14
Q

What is the catalyst when alcohols are produced by hydration of alkenes?

A

Solid phosphoric acid catalyst (also possible with concentrated sulphuric acid)

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15
Q

What will be the purity of the ethanol produced by hydration of ethenes?

A

> 90%

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16
Q

What is the overall symbol equation for when ethanol is produced from ethene by hydration?

A

CH₂=CH₂ + H₂O ⇌ CH₃CH₂OH

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17
Q

What is the overall word equation for when ethanol is produced from ethene by hydration?

A

Ethene + Water ⇌ Ethanol

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18
Q

What are the conditions for the production of alcohol through hydration of alkenes?

A
  • solid phosphoric acid catalyst
  • 300°C
  • 60atm
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19
Q

What of type pressures and temperatures are required for hydration of alkenes?

A

High temperatures and pressure (300­°C and 60atm)

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20
Q

How are alcoholic drinks produced?

A

Fermentation of glucose

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21
Q

What happens during the fermentation of glucose to form alcohol?

A
  • carbohydrates from plants are broken down into sugars (e.g. glucose)
  • this is converted to ethanol and carbon dioxide
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22
Q

What is the fermentation of glucose catalysed by?

A

The action of enzymes (zymase) in yeast

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23
Q

What is the optimum temperature for zymase enzymes in yeast?

A

30-40°C

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24
Q

What is the overall symbol equation for the fermentation of glucose to produce ethanol?

A

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

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25
Q

Which alcohol is produced when glucose is fermented?

A

Ethanol

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26
Q

What temperature is the fermentation of glucose carried out at?

A

30-40°C

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27
Q

Why is the fermentation of glucose carried out at 30-40°C?

A

Any lower, reaction would be too slow and any higher, the enzymes would be denatured

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28
Q

Why must the fermentation of glucose be carried out in the absence of air?

A

To prevent oxidation of ethanol to ethanoic acid

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29
Q

What type of respiration is the fermentation of glucose?

A

Anaerobic

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30
Q

When can ethanol be classed as a biofuel?

A

When it has been produced by fermentation, as the raw material used is plant material

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31
Q

What is a biofuel?

A

A fuel produced from renewable biological resources

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32
Q

Is ethanol produced from ethene a biofuel?

A

No - ethene is from crude oil, obtained by fractional distillation

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33
Q

When fermenting glucose to form alcohol, what happens when the fermenting solution contains about 15% ethanol?

A

The enzymes are unable to function and fermentation stops

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34
Q

How is ethanol removed from the fermenting solution?

A

Fractional distillation

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35
Q

Why can ethanol be removed from the fermenting solution by fractional distillation?

A

Because ethanol and water have different boiling points

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36
Q

Is the combustion of ethanol exothermic or endothermic?

A

Exothermic

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37
Q

What is the balanced symbol equation for the combustion of ethanol?

A

C₂H₅OH + 3O₂ → 3H₂O + 2CO₂

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38
Q

What can the energy produced from the combustion of ethanol be used to power?

A

Vehicles, and is increasingly being used in cars

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39
Q

What is a carbon neutral activity?

A

When there are no net carbon emissions

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40
Q

Why is ethanol from fermentation of glucose said to be carbon-neutral?

A
  • releases carbon dioxide when produced and burned

* but plant material from which it is made from absorbs carbon dioxide from the atmosphere during photosynthesis

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41
Q

How can ethanol produced by fermentation of glucose shown to be carbon-neutral using symbol equations?

A
  • photosynthesis - 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (6 mols taken in)
  • fermentation - C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (2 mols produced)
  • combustion - 2C₂H₅OH + 6CO₂ → 4CO₂ + 6H₂O (4 mols produced)
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42
Q

What does proving that fermentation of glucose by symbol equations not take into account?

A
  • planting & harvesting
  • preparation of plants for fermentation
  • fermentation process
  • fractional distillation
  • transportation
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43
Q

Advantages of producing alcohol by hydration of alkenes?

A
  • cheap - ethene is cheap and not much wasted
  • fast
  • continuous process - low labour costs
  • pure product
  • no waste products
  • doesn’t use crops that could’ve been used for food
  • extracting is fast and reliable
44
Q

Disadvantages of producing alcohol by hydration of alkenes?

A
  • uses crude oil - non-renewable, although now fairly cheap to obtain, as resources run out it will be more expensive
  • high amount of energy needed for the process
  • expensive equipment needed for continuous process
45
Q

Advantages of producing alcohol by fermentation of glucose?

A
  • glucose is from plants which can be grown again - renewable
  • could be seen as carbon neutral as when plant grows it takes in CO₂ for photosynthesis and balances the CO₂ released when fermented
  • high energy not needed - low cost due to low temp
  • places like Brazil - more employment, beneficial to economy
46
Q

Disadvantages of producing alcohol by fermentation of glucose?

A
  • 2 stage process
  • very slow
  • batch process
  • when ethanol concentration reaches 15% yeast stops functioning and fermentation stops
  • product obtained is not pure
  • 15% mixture must be purified by distillation - extra cost
  • CO₂ is produced
  • ethical issue - whether we should use crops for ethanol where there are developing countries with no food
47
Q

What are primary alcohols?

A

Alcohols which have one alkyl group attached to the carbon which has the -OH group attached

(ie functional group is at the end of the chain)

48
Q

What are secondary alcohols?

A

Alcohols which have two alkyl groups attached to the carbon which has the -OH group attached

49
Q

What are tertiary alcohols?

A

Alcohols which have three alkyl groups attached to the carbon which has the -OH group attached

50
Q

What must you ensure when drawing the displayed formula for alcohols?

A

The bond between the O and H must be shown

51
Q

What can oxidation in organic chemistry be regarded as?

A

The addition of oxygen; or the removal of hydrogen

52
Q

How can the oxidising agent be represented in full equations?

A

[O]

53
Q

Why is the oxidising agent represented as [O] in equations?

A

Full equations are quite complex

54
Q

What can primary alcohols be initially oxidised to?

A

Aldehydes

55
Q

What must be happening when alcohols are oxidised in order for aldehydes to form?

A

Must be distilled off

56
Q

What happens in the oxidation of primary alcohols, if the aldehyde is not distilled off?

A

The reaction is carried out under reflux and a carboxylic acid is formed

57
Q

What happens when a primary alcohol is oxidised during distillation?

A

An aldehyde is formed

58
Q

What happens when a primary alcohol is oxidised under reflux?

A

A carboxylic acid is formed

59
Q

When a primary alcohol is oxidised under reflux, is the oxidising agent limiting or in excess?

A

In excess

60
Q

When reflux apparatus is set up to obtain carboxylic acid from a primary alcohol, what is the condenser for?

A

To stop the evaporation of the aldehyde

61
Q

What is formed when a secondary alcohol undergoes oxidation?

A

A ketone

62
Q

Why are carboxylic acids not formed from secondary alcohols?

A

Ketones cannot be oxidised

63
Q

Why can’t ketones be oxidised?

A

There is no C-H bond which an oxygen atom can be inserted

64
Q

Can tertiary alcohols be oxidised?

A

No

65
Q

Why can’t tertiary alcohols be oxidised?

A

There no hydrogen on the carbon containing the alcohol group

66
Q

What is the oxidising agent used when oxidising 1°, 2° and 3° alcohols?

A

Potassium dichromate

67
Q

Symbol for potassium dichromate?

A

K₂Cr₂O₇

68
Q

What colour does potassium dichromate go when it has oxidised with a 1° alcohol?

A

Green

69
Q

What colour does potassium dichromate go when it has oxidised with a 2° alcohol?

A

Green

70
Q

What colour does potassium dichromate go when it has oxidised with a 3° alcohol?

A

Remains orange

71
Q

What happens when potassium dichromate is reduced?

A

Changes colour from orange to green

72
Q

Why does potassium dichromate change colour from orange to green in the presence of 1° and 2° alcohols?

A

It is reduced

73
Q

What happens to potassium chromate in the presence of 1° and 2° alcohols?

A

It reduces itself, and changes colour from orange to green

74
Q

Why are Tollen’s and Fehling’s reagents used to identify aldehydes?

A

They are good oxidising agents

75
Q

What do Tollen’s and Fehling’s reagents test for?

A

Aldehydes

76
Q

What do Tollen’s and Fehling’s reagents do to aldehydes?

A

They oxidise them to carboxylic acids

77
Q

How many tests can be used to test for aldehydes?

A

Two

78
Q

What is Tollen’s reagent made of?

A

Ammoniacal silver nitrate

79
Q

When will Tollen’s reagent oxidise aldehydes?

A

When boiled

80
Q

What happens when Tollen’s reagent oxidises aldehydes?

A

The colourless Ag⁺ ions are reduced to metallic silver, which form on the surface of the test tube

81
Q

What indicates an aldehyde is present when Tollen’s reagent is the oxidising agent?

A

A silver mirror

82
Q

What is Fehling’s solution made of?

A

A complex solution contained Cu²⁺ ions

83
Q

When will Fehling’s solution oxidise aldehydes?

A

When heated

84
Q

What happens when Fehling’s solution oxidises aldehydes?

A

The blue Cu²⁺ ions are reduced to the red copper (I) oxide, Cu₂O

85
Q

What indicates an aldehyde is present when Fehling’s solution is the oxidising agent?

A

A brick red precipitate (of Cu₂O)

86
Q

What can undergo elimination?

A
  • halogenoalkanes

* alcohols

87
Q

As well as alcohols, what can also undergo elimination?

A

Halogenoalkanes

88
Q

What is formed when alcohols undergo elimination?

A

Alkene

89
Q

Under what conditions are alcohols eliminated to form alkenes?

A

Heating with a concentrated sulphuric acid catalyst

90
Q

Why is elimination of alcohols also known as dehydration?

A

Alcohols lose water when they undergo elimination

91
Q

What conditions is hydration favoured by?

A

Acidic conditions

92
Q

Why are hydration reactions favoured by acidic conditions?

A

The -OH group becomes protonated by H⁺ ions

93
Q

What happens in elimination in alcohols, after the -OH group becomes protonated by H⁺ ions?

A

The -OH group that has been protonated by H⁺ ions leaves as a water molecule - forming a carbocation

94
Q

In elimination in alcohols, where does the H that is lost come from?

A

A carbon atom that is adjacent to the carbon atom attached to the OH group

95
Q

Why can there be more than one product formed from the elimination of alcohols?

A

The H which is lost can come from different carbons, as long as the carbon is next to the carbon with the OH group

96
Q

What can alkenes produced by hydration be used to make?

A

Polymers

97
Q

How can polymers be created without using crude oil?

A
  • elimination (hydration) of alcohols to produce alkenes
  • these alkenes produce polymers

(provided the original ethanol was produced by fermentation)

98
Q

General equation for the oxidation of a primary alcohol to an aldehyde?

A

RCH₂OH + [O] → RCHO + H₂O

99
Q

What is the potassium dichromate (used as an oxidising agent for alcohols) acidified with?

A

Dilute sulphric acid

100
Q

Conditions of oxidation of primary alcohols to aldehydes?

A

Warm, distillation

101
Q

General equation for the oxidation of a primary alcohol to a carboxylic acid?

A
  • RCH₂OH + [O] → RCHO + H₂O

* R-COH + [O] → R-COOH

102
Q

Conditions of oxidation of primary alcohols to a carboxylic acid?

A

Heat, reflux

103
Q

General equation for the oxidation of a secondary alcohol to a ketone?

A

R₁CH(OH)R₂ + [O] → R₁COR₂ + H₂O

104
Q

Conditions of oxidation of secondary alcohols to ketones?

A

Heat, distillation

105
Q

Reagent for elimination of alcohols to alkenes?

A

Concentrated sulphuric acid

AQA A Level Organic Chemistry (16 decks)

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