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AS Level Chemistry > Alcohols > Flashcards

Alcohols Flashcards

1
Q

What is the general formula of alcohols

A

CnH2n+1OH

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2
Q

What are the two methods alcohols can be produced by

A

Hydration and fermentation

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3
Q

What is the conditions needed for a hydration reaction (4)

A
  • Aqueous conditions
  • High Temperature
  • High pressures
  • Strong acid catalyst of concentrated Phosphoric acid
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4
Q

How does hydration produce alcohols

A
  • An alkene breaks its double bond in the presence of the catalyst turning for example c2h4 into c2h5 with one of the carbons being a carbocation
  • the carbocation gets attcked by steam(water)
  • draw an arrow from one of the lone pairs on the oxygen of the water to the C
  • Draw c2h5 with a water molecule
  • then draw c2h5oh + H+
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5
Q

What is used as a catalyst in hydration reactions

A

Phosphoric acid

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6
Q

What is the percentage yield in hydration reactions and why

A

Very high because ethanol is the only product

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7
Q

How does fermentation produce alcohols

A

Enzymes break done starch from crops into sugars which can be fermented into alcohol

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8
Q

What is the disadvantage of fermentation

A
  • Batch process which is slow
  • High production costs
  • Impure ethanol is produced which needs distilling
  • Depletes land used for growing food crops
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9
Q

Why is fermentation cheaper

A

Because it can be carried out at lower temperatures

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10
Q

What is ethanol in a fermentation reaction

A

A common biofuel

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11
Q

What is a biofuel

you dont need to learn this

A

Biofuels are liquid fuels produced from renewable biological sources, including plants and algae

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12
Q

Why is fermentation said to be carbon neutral

A

As the carbon is given out when it is burnt it is equal to the carbon taken in by the crops during the growing process

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13
Q

What type of alcohols aren’t easily oxidised

A

Tertiary

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14
Q

What alcohols can be oxidised to produce various products

A

Primary and secondary

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15
Q

What can primary alcohols produce

A

Aldehydes and carboxylic acids

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16
Q

What can secondary alcohols produce

A

Ketones

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17
Q

How are primary alcohols turned into carboxylic acids

A

When heated further under reflux conditions they oxidised further

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18
Q

How are primary alcohols turned into aldehydes

A

Heated in the presence of acidified potassium dichromate and distilled

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19
Q

Potassium dichromate formula

A

K2Cr2O7

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20
Q

How are secondary alcohols turned into ketones

A

Oxidised when heated in the presence of acidified potassium dichromate

21
Q

How can alkenes be formed

A

By the dehydration of alcohols where a water molecule is removed

22
Q

What does potassium dichromate act as in the oxidation of alcohols

A

Oxidising agent

23
Q

What is reduced and oxidised in an oxidisation of alcohols

A

Potassium dichromate is is reduced and the alcohol is oxidised

24
Q

What is the colour change when a alcohol is oxidised

A

Orange to green

25
Q

What conditions are needed for alkenes to be formed by the dehydration of alcohols

A

Excess hot sulfuric acid is added and aluminium oxide is used as a catalyst

26
Q

Why do alcohols have a higher boiling point than alkenes

A

Alkanes are non polar do only have vdw forces

27
Q

What is the boiling point of alcohols

A

Higher than alkanes of the equivalent length

28
Q

How does the polar OH bond arise

A

O is more electron negative than H

29
Q

How do you draw the OH bond

A

Draw a negative on the o and positive on the h, draw two lone pairs on the o and draw dashes to the h

30
Q

Why are alcohols more soluble than alkanes in water

A

They can form hydrogen bond with water molecules and alkanes cannot

31
Q

What is reflux used for

A

Full oxidisation of primary alcohol to carboxylic acid

32
Q

What happens in reflux to any vapours that evaporate cool and condense and drip back into the reaction mixture

A

They repeat this until it is all oxidised to the acid

33
Q

What happens to the carboxylic acid to separate it from the reaction mixture
Distillation

A

Distillation

34
Q

What reagents are used in reflux

A

Concentrated sulfuric acid and excess potassium dichromate

35
Q

What is distillation used for

A

Partial oxidation of a primary alcohol to a aldehyde

36
Q

What happens to the aldehyde as it is formed

A

Distilled to prevent further oxidation

37
Q

What reagents are used in distillation

A

Dilute acid and less potassium dichromate

38
Q

Functional group for aldehyde

A

Double bond o at the end

39
Q

Functional group for ketone

A

Double bond o in the middle

40
Q

What types of reactions do alcohols undergo

A

Combustion and elimination

41
Q

What are the two methods of elimination

A

Pass vapours over al2o3 catalyst or react with h3po4 or conc h2so4

42
Q

Method of distillation for alcohols

A

Heat organic product in the round bottom flask using an electric heater, place thermometer at t junction, use a condenser with the water going in at the bottom, collect distillate and use an ice bath to cool the distillate

43
Q

Why should you never seal the end of the condenser

A

The build up of gas could cause the apparatus to explode

44
Q

What are anti bumping granules used for

A

Provide a surface for small bubbles to form on

45
Q

Reaction between ketones and tollens reagent

A

Heat gently and a silver mirror forms inside o the test tube

46
Q

How can aldehydes be distinguished from ketones

A

Ketones don’t react with tollens reagent

47
Q

How can the presence of a carboxylic acid be tested

A

Add sodium carbonate and it will fix and produce carbon dioxide

48
Q

Why do some people say biofuel isn’t carbon neutral

A

Transportation costs, energy is used when distilling

AS Level Chemistry (14 decks)

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