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chemistry A - level > organic chem - alcohols > Flashcards

organic chem - alcohols Flashcards

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1
Q

alcohols
functional group
name
general formula

A

-O-H
-ol
Cn H2n+1 OH

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2
Q

What are the two main methods of forming alcohols?

A
  • hydration of ethene
  • fermentation
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3
Q

hydration of ethene

A

produces alcohols from alkenes in the presence of an acid catalyst. usually conc. sulphuric acid, H2SO4/ phosphoric acid H3PO4 under aq conditions. high temp and pressure

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4
Q

why is the hydration of ethene a favourable industrial process

A

very high percentage yield as ethanol is the only product

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5
Q

disadvantages of the hydration of ethene?

A
  • expensive due to high temp and pressure
  • source of ethene is crude oil
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6
Q

what happens in the fermentation process?

A

enzymes break down starch form crops into sugars which are fermented to form alcohol. its a cheaper method as it down in low temp (30 degrees), in anaerobic conditions with yeast

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7
Q

why is fermentation not favoured as a process

A

its made in batches so its slower and has a lower % yield, and produces CO2

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8
Q

why is ethanol (common biofuel) said to be carbon neutral?

A

carbon given out when its burned is equal to the carbon taken in by the crops during this process

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9
Q

What molecules are alcohols

A

Polar molecules due to polar O-H bond

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10
Q

The effect of the chain on the polarity of an alcohol

A

The longer the carbon chain the less polar it becomes

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11
Q

The boiling point for alcohols

A

The O-H allows for hydrogen bonding. The boiling point for alcohols are significantly higher than the respective alkane and alkene

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12
Q

does the place where O-H group is affect the alcohols properties?

A

yes, the physical properties and reactions can be affected

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13
Q

what are the classifications of alcohols?

A

primary alcohol
secondary alcohol
tertiary alcohol

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14
Q

reaction of alcohols
dehydration

A

its a type of reaction not a mechanism, that form’s alkenes through the loss of H20

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15
Q

what is the mechanism for dehydration of alcohols and their conditions?

A

elimination
- high temp and pressure
- excess concentrated acid catalyst (H2SO4)
- aluminium oxide added

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16
Q

oxidation of alcohols

A

in the presence of an oxidising agent, we can form new functional groups from alcohols

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17
Q

what happens when you distil a primary alcohol in an oxidation reaction?

A

forms an aldehyde
- al
CO=H

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18
Q

what happens when you distil and reflux a primary alcohol in an oxidation reaction?

A

forms a carboxylic acid
- oic acid
CO=OH

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19
Q

what happens when you reflux a secondary alcohol in an oxidation reaction?

A

forms a ketone
- one
CO=

20
Q

what happens when with a tertiary alcohol in an oxidation reaction?

A

no reaction
resistant to oxidation

21
Q

most common oxidising agent

A

acidified potassium dichromate K2Cr2O7

22
Q

starting and ending colour of K2Cr2O7

A

start (Cr2O72-) - orange
end (Cr3+) - green
gains 3 electrons so its being reduced

23
Q

order of boiling points:
- propanal
- propanone
- propanoic acid

A

propanoic acid is the highest as hydrogen bonding is possible
propanone
propanal

24
Q

which can be oxidised aldehydes or ketones?

A

aldehydes

25
Q

reactions of aldehydes

A

fehling’s test
tollens reagent

26
Q

what is fehlings test?

A

contains a weak oxidising agent that can oxidise aldehydes, heated
result for al - blue solution to an orange precipitate
result for one - remains blue

27
Q

what is the silver mirror test using tollens reagent

A

produces ammonia, warmed gently
result for al - colourless solution to silver/ black precipitate
result for one - stays colourless

28
Q

tests for carboxylic acids

A
  • indicator to test pH (r pH meter)
  • add alcohol and acid catalyst
  • add a solid carbonate/ hydrogen carbonate
29
Q

the addition of alcohol and acid catalyst to test for a carboxylic acid

A

result = fruity smell due to ester formation

30
Q

the addition of a solid carbonate/ hydrogen carbonate to test for a carboxylic acid

A

observation = fizzing/ gas produced/ bubbling
result for ketone = nothing

31
Q

what is high resolution mass spectrometry?

A

is able to measure Mr to more decimal places (4 or 5).at this resolution, molecules with the ‘same Mr’ to 1dp can be distinguished, more sensitive

32
Q

what is infra-red spectroscopy?

A

IR spectroscopy is a useful analytical technique used to identify functional groups in a molecule

33
Q

how does IR spectroscopy work?

A

bonds vibrate and can absorb IR radiation to get ‘excited’. different functional groups absorb different wavelengths of this radiation

34
Q

transmission % on 2250

A

single bonds
C - H
C- N
N - H
O - H

35
Q

transmission % on 2000

A

Triple bonds
C =- N

36
Q

transmission % on 1500

A

double bonds
C =C
C = O

37
Q

transmission % on less than 1500

A

fingerprint region
completely unique for a molecule

38
Q

shapes of alcohols on a IR spectroscopy

A

U -shaped curves

39
Q

shapes of carboxylic acids on a IR spectroscopy

A

wide V -shaped curves

40
Q

what is the purpose of small glass beads in the round-bottomed flask

A

to prevent bumping

41
Q

why is it important to open the tap of the separating funnel

A

avoid pressure build up

42
Q

Fractional distillation of ethanol

A
  • turn on water
  • heat flask, with a Bunsen burner
  • causes water & ethanol vapours to be produced
  • vapour pass up the fractionating column
  • water & ethanol are separated in it
  • water condenses back in the fractionating column
  • observe the thermometer to keep the temp at or below the boiling point of ethanol
  • use the condenser to cool the vapour and condense the ethanol back into a liquid
43
Q

What is global warming

A

absorption occurs in atmosphere with molecules,e.g. ozone, heat is trapped within the earths atmosphere. when CFCs are released, this heating effect is enhanced leading to global warming

44
Q

How are addition polymers produced

A

from fermentation without the need for crude oil. produces the primary alcohol, which is dehydrated to produce an alkene, which is using a production of addition polymers

45
Q

Suggest why sodium carbonate solution was used to wash the distillate

A

Neutralise acid

46
Q

Give a property of anhydrous calcium chloride, other than its ability to absorb water, that makes it suitable as a drying agent in this preparation

A

Does not dissolve with the cyclohexene

chemistry A - level (16 decks)

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