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Chemistry A Level 2023 2 organic > alcohols > Flashcards

alcohols Flashcards

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1
Q

general formula for alcohol

A

CnH2n+1OH

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2
Q

intermolecular forces in alcohols

A

hydrogen bonding due to OH bond

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3
Q

how do alcohols mp and bp compare with hydrocarbons’ of similar C chain lengths

A

higher because of hydrogen bonding compared to van der waals

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4
Q

are alcohols soluble in water? why does solubility depend on chain length?

A

soluble short chain
insoluble long chain
OH hydrogen bonds with water, but in long chains non-polarity takes precedence

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5
Q

primary alcohol

A

C bonded to OH is only bonded to one other C atom

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6
Q

what makes an alcohol secondary

A

C bonded to OH bonded to 2 other C atoms

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7
Q

what makes an alcohol tertiary

A

C bonded to OH is bonded to three other C atoms

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8
Q

how can ethanol be made from crude oil

A

hydration of ethene via electrophilic addition
(phosphoric acid catalyst H3PO4)

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9
Q

advantages and disadvantages of making ethanol from crude oil

A

advantages:
fast, continuous process, ethanol has high purity

disadvantages:
not renewable as from crude oil

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10
Q

how can ethanol be made from fermentation

A

plant carbohydrates broken down and fermented by enzymes in yeast –> ethanol

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11
Q

what conditions are needed for this reaction to take place

A

enzymes in yeast as a catalyst
35 degrees C
anaerobic conditions

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12
Q

equation for reaction which takes place

A

C6H12O6 (aq) –> 2C2H5OH + 2CO2

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13
Q

what are the advantages and disadvantages of ethanol from fermentation

A

advantages:
renewable as from plants

disadvantages:
slow
batch process
enzymes stop working at 15% alcohol so solution is not pure
needed to be fractionally distilled

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14
Q

in the future, how might most ethene be made? why is it not made like this at the moment

A

dehydrate ethanol made by fermentation –> ethene

not economical at the moment

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15
Q

define carbon neutral

A

no net addition of CO2 to the atmosphere - COs released when combusted = CO2 absorbed as a plant

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16
Q

explain how using ethanol in petrol engines could be considered to be carbon neutral

A

CO2 released in fermentation and combustion = CO2 absorbed when growing

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17
Q

why would it probably not be entirely carbon neutral to use ethanol in petrol engines

A

other carbon costs such as transport

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18
Q

what is a commercial fuel that uses ethanol and what does it contain and why

A

methylated spirits contains methanol which is toxic so can’t be drunk

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19
Q

write an equation for combustion of ethanol

A

C2H5OH (l) + 3O2 (g) –> 2CO2 (g) + 3H2O (l)

20
Q

what is an elimination reaction

A

removal of a smaller molecule from a larger one

21
Q

which groups leaves the parent molecule in the case of alcohols

A

OH and a H (to form water)

22
Q

what physical conditions are needed for the elimination reaction from alcohols to alkenes

A

excess hot concentrated sulphuric acid
OR
pass vapour over hot aluminium oxide

23
Q

what forms if you partially oxidise a primary alcohol

A

an aldehyde

24
Q

what conditions are needed to partially oxidise a primary alcohol

A

dilute sulphuric acid, potassium dichromate (VI), distill product as its produced, gentle heating

25
Q

equation for partial oxidation of ethanol

A

CH3CH2OH (l) + [O] –> CH3CHO (g) + H2O (l)

26
Q

what forms if you fully oxidise a primary alcohol

A

carboxylic acid

27
Q

what conditions are needed for this reaction

A

concentrated sulphuric acid, potassium dichromate (VI), reflux for about 20 mins, strong heating

28
Q

write an equation for full oxidation of ethanol

A

CH3CH2OH (l) + 2[O] –> CH3COOH (g) + H2O (l)

29
Q

what forms if you oxidise a secondary alcohol

A

ketone

30
Q

why can a ketone not be oxidised further? why can’t a tertiary alcohol be oxidised?

A

carbon-carbon bond would have to break

31
Q

what conditions are needed for the oxidation of a secondary alcohol

A

concentrated sulphuric acid,
potassium dichromate (VI),
reflux for about 20 mins,
strong heating

32
Q

write an equation for the oxidation of propan-2-ol

A

CH3CH(OH)CH3 (l) + [O] –> CH3COCH3 (g) + H2O (l)

33
Q

what is an aldehyde and what is its functional group

A

molecule with C=O group at end of carbon chain

34
Q

suffix for aldehyde

A

-al

35
Q

what is a ketone

A

molecule with C=O in middle of carbon chain

36
Q

suffix for ketone

A

-one

37
Q

what is a carboxylic acid

A

molecule with COOH at end of carbon chain

38
Q

suffix for carboxylic acid

A

-oic acid

39
Q

what does Tollens’ test give positive result for

A

aldehydes

40
Q

what is in tollens reagent and how does it react with substance tested

A

silver nitrate in NH3 (aq)

oxidises aldehydes but not ketones

complex silver (I) ions reduced to Ag (s) giving silver mirror

41
Q

how do you carry out Tollens test

A

equal volumes of substance being tested and tollens reagent to a test tube and leave in water bath to observe changes

42
Q

result of the Tollen’s test for aldehydes and ketones

A

aldehydes = silver mirror
ketones = no visible change

43
Q

what does Fehlings solution give +ve test for

A

aldehydes

44
Q

what is Fehlings

A

blue copper (II) complex ions - gentle oxidising agent

reduced to Cu+ ions (brick red)

45
Q

what conditions do you need to use the Fehling’s solution

A

heat

46
Q

what result do aldehydes and ketones give in Fehlings

A

aldehyde = brick red
ketone = no visible change

Chemistry A Level 2023 2 organic (16 decks)

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