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Chemistry > Alcohols > Flashcards

Alcohols Flashcards

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1
Q

Why do alcohols have higher melting and boiling points than their analogous alkanes?

A
  • ethanes strongest IMF is van de walls
  • Ethanols strongest bonds are hydrogen bonds
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2
Q

Why are short alcohols soluble in water? Why do alcohols become less soluble as chain length increases?

A
  • water and short chain alcohols both contain hydroxyl group and this can form hydrogen bonds with each other
  • as chain length increases, as the non-polar hydrocarbon chain cannot form hydrogen bonds, a greater part of the molecule is unable to form H bonds with water molecules
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3
Q

Why are alcohols useful from chemical synthesis?

A
  • as they are used as intermediates and as solvents
  • used as starting materials for the production of many other substances
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4
Q

What are the conditions for fermentation?

A
  • glucose
  • 35C
  • anaerobic
  • yeast
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5
Q

Why must air be kept out of the reaction vessel (fermentation)

A
  • to prevent ethanol from oxidising (ethanol acid)
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6
Q

Does fermentation have high or low atom economy?

A
  • low
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7
Q

What does hydration mean?

A
  • adding water across double bond
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8
Q

What are the conditions for hydration of ethane?

A
  • 573K
  • 60-70atm
  • H3PO4 catalyst
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9
Q

What is a biofuel?

A
  • fuel made from renewable resources
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10
Q

What does carbon neutral mean?

A
  • the CO2 released by burning fuels is absorbed by plants from which it was obtained
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11
Q

Why might ethanol not be described as a carbon neutral fuel?

A
  • uses energy for all steps
  • transport + fertiliser + machinery in farming
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12
Q

Aldehydes ketones and carboxylic acids contain…

A
  • the C=O (carbonyl) functional group
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13
Q

What is the functional group for an aldehyde

A

Suffix-al

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14
Q

What is the functional group for a ketone?

A
  • suffix-one
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15
Q

What is a carboxylic acid>

A
  • R-COOH
  • suffix-oic acid
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16
Q

What is the strongest IMF in an aldehyde?

A
  • dipole-dipole
17
Q

Describe the oxidation of primary alcohols

A
  • primary alcohols can be oxidised to aldehydes
  • aldehydes can be further oxidised to carboxylic acids
18
Q

What is the oxidising agent in the oxidation of primary alcohols?

A
  • acidified potassium dichromate
  • H+/K2Cr2O7
19
Q

Describe the colour of potassium dichromate

A
  • K2Cr2O7 is orange due to the presence of Cr2O7 2- ions
  • when it oxidises a primary alcohol or an aldehyde it turns green as Cr2O72- ions are reduced to Cr3+ ions
20
Q

How is ethanol oxidised?

A
  • distillation
  • produces an aldehyde + water
  • H+ in H+/K2Cr2O2 is supplied by a dilute acid
  • oxidising agent is added to alcohol to ensure it is never in excess
  • mixture is heated gently and distilled immediately
  • to maximise the yield for aldehyde the temperature must be kept below boiling point of the alcohol and the collecting vessel should be cool
  • ethanal has a boiling point of 21C so it vaporises as soon as it forms
  • CH3CH2OH + [O] -> CH3CHO + H2O
21
Q

How is an alcohol/aldehyde oxidise to a carboxylic acid?

A
  • reflux
  • the H+/Kr2Cr2O7 is supplied by a concentrated acid and is added in excess
  • orange to green
  • after refluxing for around 20 mins, the ethanol I acid that is formed has a boiling point of 118C. The apparatus is rearranged to that for distillation, so it can be distilled off along with any water
22
Q

What is the general equation of an alcohol to a carboxylic acid?

A
  • R-CH2OH + 2[O] -> R-COOH + H2O
  • 2 Oxidation steps
  • H2O is producded in step 1 only
23
Q

What is the equation for the oxidation of ethanol -> ethanoic acid?

A

CH2CH2OH + 2[O] > CH3COOH + H2O

24
Q

Describe oxidation of secondary alcohols

A
  • secondary alcohols are oxidise to ketones using H+/K2Cr2O7 under reflux conditions
  • orange to green
  • byproduct of water
25
Q

Why can ketones not be oxidise further?

A
  • no available hydrogen atoms on the carbonyl carbon
26
Q

Why can tertiary alcohols not be oxidised?

A
  • no available hydrogen atoms on the carbon with the -OH group attached
27
Q

How do you test for a carboxylic acid?

A
  • add carbonate
  • test for CO2
28
Q

How do you use tollens reagent to test for aldehydes?

A
  • add ammonical silver nitrate as it contains Ag+ ions
  • Ag+ will be reduced to Ag
  • aldehyde is oxidised to the carboxylic acid
  • formation of silver mirror (shows aldehyde has been oxidised)

R-CHO + [O] -> R-COOH

29
Q

How do you use fehlings solution test for an aldehyde

A
  • fehlings solution containers a copper (II) complex containing Cu2+ ions which are blue
  • during the test the Cu2+ ions are reduced to Cu+ ions which are red
  • Cu2+ + e- -> Cu+
  • formation of a brick red precipitate
    R-CHO + [O] -> R-COOH
30
Q

What are the reagents for dehydration of alcohols?

A
  • Hot conc H2SO4
  • Hot conc H3PO4
  • Hot Al2O3
31
Q

What is the apparatus for dehydration of ethanol when hot AL2O3 is used?

A
32
Q

What is the apparatus when hot concentrated acid is used for dehydration of ethanol?

A
33
Q

What are the reagents, products, and conditions for a dehydration of alcohol reaction?

A
  • reagents: ethanol and hot Al2O3 or hot conc H3PO4
  • conditions: ethanol vapourised
  • ethanol -> ethene + H2O
34
Q

Outline the mechanism of the dehydration of ethene

A
35
Q

What is refluxing?

A
  • mixture is heated vigorously into a vapour
  • the vapour that condenses is then trapped and returned to the reaction mixture, forcing it (the initial aldehyde product) to be oxidised further (to a carboxylic acid)

Chemistry (13 decks)

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