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A-level Chemistry > 4.2.1 Alcohols > Flashcards

4.2.1 Alcohols Flashcards

1
Q

Are alcohols soluble in water?

A
  • likely to be soluble in water due to similar strength attractions between water and alcohol molecules
  • alcohol molecules are able to form hydrogen bonds with water due to polar -OH group
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2
Q

Why does solubility decrease with chain length?

A
  • a larger part of the molecule is made up of non-polar carbon-hydrogen bonds
  • the hydrocarbon chain does not form hydrogen bonds with water molecules
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3
Q

Are alcohols polar?

A
  • the O-H functional group is polar due to differences in electronegativities between oxygen and hydrogen
  • there is a electron deficient hydrogen that can form hydrogen bonds
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4
Q

Draw a diagram to show the hydrogen bonding in alcohol molecules

A

See notes

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5
Q

Why are alcohols less volatile than alkanes?

A
  • low volatility = higher bpt
  • alcohol molecules have hydrogen bonds between molecules
  • alkanes only have London forces between molecules
  • more energy is needed to overcome hydrogen bonds as they are stronger than London forces
  • alcohols have a higher bpt
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6
Q

What is a primary alcohol?

A
  • an alcohol with one alkyl group attached to C-OH
  • e.g. propan-1-ol
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7
Q

Draw a primary alcohol

A

See notes
(Propan-1-ol)

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8
Q

What is a secondary alcohol?

A
  • an alcohol with 2 alkyl groups attached to C-OH
  • e.g. butan-2-ol
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9
Q

Draw a secondary alcohol

A

See notes
(Butan-2-ol)

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10
Q

What is a tertiary alcohol?

A
  • an alcohol with 3 alkyl groups attached to C-OH
  • e.g. methylpropan-2-ol
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11
Q

Draw a tertiary alcohol

A

See notes
(Methylpropan-2-ol)

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12
Q

Draw reaction for incomplete combustion of pentan-1-ol

A

See notes
(Insufficient oxygen present for complete oxidation)

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13
Q

Draw reaction for complete combustion of propan-2-ol

A

See notes
(Plentiful supply of oxygen)

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14
Q

What does a primary alcohol form when oxidised?

A
  • primary alcohol
  • aldehyde
  • carboxylic acid
  • (2 H to be removed = 2 steps)
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15
Q

What does a secondary alcohol form when oxidised?

A
  • secondary alcohol
  • ketone
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16
Q

What does a tertiary alcohol form when oxidised?

A
  • no reaction
17
Q

What are the conditions for the oxidation of primary alcohols?

A
  • acidified potassium dichromate (+heat)
  • H2SO4/K2Cr2O7
  • reaction carried out under distillation conditions to form an aldehyde
  • reaction carried out under reflux to form a carboxylic acid
  • oxidising agent represented by [O] in a reaction equation
18
Q

What colour change occurs during the oxidation of primary alcohols?

A
  • from orange to green
  • Cr(VI) = orange
  • Cr(III) = green
19
Q

Draw the oxidation of a primary alcohol to form an aldehyde

A

See notes
Under distillation conditions

20
Q

Draw the oxidation of a primary alcohol into a carboxylic acid

A

See notes
Under reflux
No H2O

21
Q

Why are distillation and reflux conditions used?

A
  • distillation - as soon as the aldehyde forms it doesn’t have time to form the carboxylic acid
  • reflux - this allows the aldehyde to condense back into the reaction flask and carry on reacting
22
Q

What is the overall equation for the oxidation of primary alcohols?

A

Primary alcohol + 2[O] -> carboxylic acid + H2O

  1. Primary alcohol + [O] -> aldehyde + H2O
  2. Aldehyde + [O] -> carboxylic acid
23
Q

How are secondary alcohols oxidised?

A
  • form ketones
  • carried out under reflux to ensure that all reactant is converted into product
24
Q

Draw the oxidation of a secondary alcohol to a ketone

A

See notes

25
Q

What are the conditions for the elimination of water from alcohols (dehydration)?

A
  • concentrated H3PO4 or H2SO4
  • under reflux for about 40mins
26
Q

What is the equation for the dehydration of alcohols?

A

See notes

27
Q

What are the conditions for the substitution of alcohols to give haloalkanes?

A
  • chlorides NaCl/c. H2SO4
  • bromides NaBr/c. H2SO4
  • iodides NaI/H3PO4
28
Q

What is the equation for the substitution of alcohols to give haloalkanes?

A

See notes

A-level Chemistry (23 decks)

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