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Chemistry Y12 > alcohols > Flashcards

alcohols Flashcards

1
Q

why will wine end up tasting sour if left opened without cork?

A

This is because the alcohol (ethanol) has been oxidised to a carboxylic acid (ethanoic acid).

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2
Q

how can we distinguish between primary, secondary and tertiary alcohols?

A

by looking at the reaction of alcohols with oxidising agents such as acidified potassium dichromate (VI)

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3
Q

what is oxidation?

A

oxidation is regarded as the gain of 1
oxygen atom (or the loss of 2 hydrogen atoms).

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4
Q

what is an oxidising agent?

A

The chemical that supplies the oxygen (or removes the hydrogen)

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5
Q

what symbol shows 1 atom of oxygen? or shows the oxidant

A

In balanced symbol equations [O] is 1 atom of oxygen.

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6
Q

what is a primary alcohol oxidised to form?

A

to form an aldehyde.

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7
Q

the aldehyde can then be further oxidised into a…?
By adding..?

A

carboxcylic acid
Excess potassium dichromate

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8
Q

give the full displayed formula reaction when ethanol is warmed with excess acidified potassium dichromate.

A

ethanol + [O] ——> ethanal and water
CH3CH2OH + [O] → CH3CHO + H2O

then

ethanal + [O] ———-> ethanoic acid
CH3CHO + [O] → CH3COOH

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9
Q

what is the overall reaction for the above reaction?

A

CH3CH2OH + 2 [O] → CH3COOH + H2O
ethanol + 2 [O] —–> carboxylic acid + water

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10
Q

what are the reaction conditions for the oxidation of primary alcohols?

A

K2Cr2O7 + (H2SO4) dilute and warm sulphuric acid

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11
Q

what colour change is observed when primary alcohols are oxidised using acidified potassium dichromate (VI)?

A

The orange solution of potassium dichromate (VI) changes to
a green solution containing chromium (III) ions.

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12
Q

how can we control the oxidation of primary alcohols?

A

By altering the reaction conditions

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13
Q

How do we control the oxidation of a primary alcohol to give us an aldehyde?

A

using distillation apparatus

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14
Q

How do we control the oxidation of a primary alcohol to give us a carboxylic acid?

A

Alcohol is oxidised under reflux

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15
Q

if a primary alcohol is oxidised using distillation apparatus…?

why does this work?

A

then any aldehyde formed will distil off immediately from the mixture.

This works because the aldehyde boiling point is lower than the corresponding alcohol and carboxylic acid.

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16
Q

if a primary alcohol is oxidised under reflux, then…?

why does this work?

A

the aldehyde cannot escape and is oxidised to form a carboxylic acid.

When reactants are heated under reflux, any volatile components will rise up the condenser, get condensed and
then return to the reaction mixture.

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17
Q

what are secondary alcohols oxidised to?

A

ketones

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18
Q

give the full displayed formula reaction when butan-2-ol is warmed with acidified potassium dichromate.

A

makes butanone

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19
Q

why can aldehydes be further oxidised but not ketones?

A

Aldehydes can be oxidised further because there is still a hydrogen atom attached to the carbon with the C=O bond.
Ketones do not have this hydrogen atom.

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20
Q

what are the reaction conditions for the oxidation of secondary alcohols

A

K2Cr2O7 + dilute H2SO4 + warm

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21
Q

When secondary alcohols are oxidised using
acidified potassium dichromate (VI) what colour change is observed?

A

The orange solution of potassium dichromate (VI) changes to a green solution containing chromium (III) ions.

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22
Q

what observation is made from tertiary alcohols and oxidising agents?

A

Tertiary alcohols are not oxidised by acidified
dichromate (VI) ions.

Therefore, no colour change is observed – the
solution stays orange.

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23
Q

why do tertiary alcohols have no reaction?

A

In contrast to 1° and 2° alcohols, 3° alcohols do not have a hydrogen atom bonded to the carbon carrying the ―OH group.

Such atoms are removed as part of the oxidation process – thus 3° alcohols are not oxidised under normal conditions.

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24
Q

Aldehydes and ketones

A
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25
Q

What does the carbonyl, aldehyde and ketone group look like?

A
  • C=O
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26
Q

Which two homologous series have the same general formula?

A

Aldehydes and ketones
CnH2nO

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27
Q

What is the difference between the aldehydes and ketones?

A

The aldehydes have a hydrogen atom attached to the carbonyl carbon atom

28
Q

Where do aldehydes have their carbonyl group n the carbon chain?

A

At the end

29
Q

Where do ketones have their carbonyl group in the carbon chain?

A

The middle

30
Q

Higher ketones have …? isomers

A

Positional isomer

31
Q

Why do aldehydes and ketones show functional group isomerism?
Give an example.

A

They’re different homologous series but have the same functional groups
E.g C3H6O can be propanal or propanone

32
Q

How can aldehydes and ketones be distinguished?

A

By using mild oxidising agents
E.g Tollen’s reagent or Fehling’s solution

33
Q

what is the active substance in tollens reagent?

A

[Ag(NH3)2]+. Silver ions in the +1 oxidation state.

34
Q

how is the active substance made?

A

The active substance is made by mixing silver nitrate and dilute aqueous ammonia.

35
Q

what happens when an aldehyde is warmed with Tollens reagent?

A

When Tollen’s reagent is warmed with an aldehyde the silver ions are reduced (by the aldehyde) to silver metal atoms.
The aldehyde is oxidised to a carboxylic acid.
A silver mirror is produced on the walls of the test tube.

36
Q

what doesn’t react with Tollens reagent?
so colour remains..?

A

ketones
colourless

37
Q

what is Fehling’s solution?

A

blue solution containing Cu2+ ions.

38
Q

what happens when an aldehyde is warmed with Fehling’s solution?

A

When an aldehyde is warmed with Fehling’s solution the Cu2+ ions are reduced to Cu+ ions (Cu2O, copper (I) oxide).
The Cu+ ions in copper (I) oxide are brick red and copper (I) oxide is insoluble.
A red precipitate is produced.
The aldehyde is oxidised to a carboxylic acid.

39
Q

what doesn’t react with Fehling’s solution?
so colour remains…?

A

ketones
blue

40
Q

Fermentation of ethanol

A
41
Q

What is fermentation?

A

In the fermentation process an aqueous solution of plant sugar e.g glucose is converted into ethanol and carbon dioxide by living yeast cells

42
Q

Write the equation for fermentation?

A

C6H12O6 —(yeast, 35degrees) -> 2C2H5OH + 2CO2

43
Q

What does the yeast contain?

A

The heat contains enzymes which catalyse the fermentation reaction

44
Q

What are the reaction conditions?

A

The reaction is carried out in
- approximately 35 degrees C in aqueous solution
- anaerobic conditions ( no oxygen)

45
Q

What would the presence of oxygen cause?

A

Cause ethanol to oxidise into ethanoic acid

46
Q

Why can’t fermentation take place under a high or low temperatures?

A

A hight temperatures - Yeast cannot survive as the enzymes are denatured

At low temperatures - enzymes in yeast are not activated and the reaction is very slow

47
Q

What is a batch process?

A

The reactant are mixed together, once the reaction is over the products are removed and the process is started all over again

48
Q

How is the ethanol separated from fermented products?

A

Fractional distillation

49
Q

What is fermentation used to make?

A

Alcoholic drinks, bread and biofuel

50
Q

Compare the advantages and disadvantages of making ethanol by direct hydration of ethene compared to fermentation

A

Direct hydration - continuous process- cheap on manpower, requires expensive equipment and high energy, reaction if fast, pure ethanol and high yield, finite resource used

Fermentation - batch process- expensive on manpower, cheap equipment low energy, slow reaction, ethanol is impure and low yield, renewable resource used

51
Q

What type of fuel is ethanol?

A

Ethanol made by fermentation is a biofuel

52
Q

What is biofuel?

A

Biofuels are made from plants or biomass (material derived from plants)

53
Q

Are biofuels non-renewable or renewable?

A

Renewable because plants can be grown again quickly

54
Q

Compare biofuels with fossil fuels

A

Fossil fuels take millions of years to form and are finite whereas biofuels are quickly grown and renewable

55
Q

Ethanol as a biofuel can be considered…?

A

Carbon neutral

56
Q

What is a carbon neutral activity?

A

A carbon neutral activity is one that has no net annual carbon (greenhouse gases) emissions to the atmosphere

57
Q

Why is ethanol biofuel considered carbon neutral?

A
  • amount of carbon dioxide made during ethanol combustion + amount of carbon dioxide released by ethanol formation (by fermentation) = amount of carbon dioxide removed from the atmosphere during photosynthesis
58
Q

Why is fermentation considered by some people not carbon neutral?

A
  • processing steps require energy
  • production of this energy may involve the release of additional carbon dioxide
  • the land area used to grow crops for fermentation may lead to deforestation
  • trees act as natural stores of co2 and cutting them will release
  • also less land available for growing crops for food (developing countries)
59
Q

Dehydration of alcohols

A
60
Q

Alcohols can also undergo…? Reactions

A

Elimination reactions

61
Q

Why is this reaction referred to as a dehydration reaction?

A

Water is eliminated in this reaction

62
Q

Draw a word equation to show the dehydration of an alcohol to produce an..?

A

Alcohol —-> (heat/acid catalyst) –> Akene + water

63
Q

Outline the dehydration of ethanol by elimination

A
64
Q

Alkanes made by elimination can be used as..?

A

Starting material for addition polymerisation reactions

65
Q

Why is this alternative route to making addition polymers better than the usual route

A

The usual route starts or with crude oil

Fermentation of plant sugars —> crude oil (fractional distillation) —> alkanes (cracking) —-> alkenes (addition polymerisation) —> polymers

66
Q

Draw using arrows the alternative route

A

Alcohols —(dehydration)—> Alkenes —(addition polymerisation) —> polymers

67
Q

FINISH

A

Chemistry Y12 (11 decks)

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