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A LEVEL CHEM > 3.5 Alcohols > Flashcards

3.5 Alcohols Flashcards

1
Q

what are alcohols?

A
  • a compound with an -OH group, with a general formula CnH2n+1OH
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2
Q

do alcohols have generally high or low boiling points?

A
  • high, due to their ability to form hydrogen bonds between alcohol molecules
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3
Q

why can smaller alcohols dissolve in water?

A
  • they can form hydrogen bonds to water molecules
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4
Q

what are the three types of alcohols?

A
  • primary, secondary and tertiary
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5
Q

what is the oxidising agent used to oxidise alcohols?

A
  • potassium dichromate
  • K2Cr2O7
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6
Q

give the reagent, reaction and conditions for the partial oxidation of primary alcohols

A

reaction - primary alcohol into aldehyde

reagent - potassium dichromate solution and dilute sulfuric acid

conditions - warm gently and distil out the aldehyde as it forms

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7
Q

what is the observation for oxidation of primary alcohols?

A
  • the orange dichromate ion reduces the green Cr3+ ion
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8
Q

when writing oxidation equations, how do we express the oxidising agent?

A

[ O ]

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9
Q

what is distillation?

A
  • a technique used to seperate an organic product from its reacting mixture
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10
Q

how can we maximise the yield collected from distillation?

A
  • collect the distillate at the approximate boiling point of the desired aldehyde and not higher
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11
Q

why are electrical heaters often used to heat organic chemicals?

A
  • because organic chemicals are normally highly flammable and could set on fire with a naked flame
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12
Q

how can we help improve the yield of the distillate?

A
  • collection flask can be cooled with ice
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13
Q

what are the main parts of the distillation equipment?

A
  • thermometer
  • liebig condenser
  • water out then water in
  • round bottomed flask
  • collection flask
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14
Q

what are the reagents, conditions and reaction for the full oxidation of primary alcohols

A

reaction - primary alcohol to carboxylic acid

reagent - potassium dichromate solution and sulfuric acid

conditions - excess dichromate, heat under reflux

distill off product after reaction finished

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15
Q

what is the equation for full oxidation of primary alcohol

A

RCOH + 2[O] > RCOOH + H2O

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16
Q

when is reflux used?

A
  • when heating organic reaction mixtures for long periods
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17
Q

how does the condenser work in reflux!

A
  • prevents organic vapours from escaping by condensing them back to liquids
18
Q

why should you never seal the end of the condenser

A

build up of gas pressure could cause the apparatus to explode

19
Q

why are antibumping granules added to the flask?

A
  • to prevent vigorous, uneven boiling by making small bubbles form instead of large bubbles
20
Q

give the reaction, reagents and conditions for oxidation of secondary alcohols

A

reaction - secondary alcohol to ketone

reagent - potassium dichromate solution and dilute sulfuric acid

conditions - heat under reflux

21
Q

why cant tertiary alcohols be oxidised?

A
  • no hydrogen atom bonded to the carbon with the -OH group
22
Q

how can i distinguish between aldehydes and ketones?

A

tollens’ reagent or fehling’s solution

23
Q

how can tollens reagent be formed?

A
  • mixing aqueous ammonia and silver nitrate
  • the active substance is the complex ion of [Ag(NH3)2]+
24
Q

give the reaction and observation for tollens reagent

A
  • aldehydes only are oxidised by tollens reagent into a carboxylic acid
  • silver ions recues to silver atoms
  • a silver mirror forms inside test tube
25
Q

give the reaction and observations for fehlings solution

A
  • aldehydes only are oxidised by Fehling’s solution into a carboxylic acid
  • copper ions reduced to copper oxide
  • Blue copper ions change to red precipitate of Cu2O
26
Q

how can the presence of a carboxylic acid be tested?

A
  • addition of sodium carbonate
  • it will fizz and produce CO2
27
Q

what is meant by dehydration reaction?

A
  • removal of a water molecule from a molecule
28
Q

give the reaction, reagents conditions and role of reayent for the reaction of alcohols with dehydrating agents

A

reaction - acid catalysed elimination

reagent - concentrated sulfuric acid or phosphoric acid

conditions - warm (under reflux )

role of reagent - dehydrating agent

29
Q

give the equation for alcohol to alkene in acid catalysed elimination

A

alcohol > alkene + water

30
Q

draw on a sheet of paper the acid catalysed elimination mechanism

A

arrow from lone pair on O: to H+
positive O formed gaining a H
arrow from C-O bond to O+
arrow from C-H to C-C+
C=C forms

31
Q

what are the two ways of producing ethanol

A
  • fermentation and from ethene
32
Q

give the conditions and type of reaction for production of ethene from fermentation

A
  • yeast
  • no air
  • temperatures 30-40

fermentation

33
Q

why is the optimum temp 38 for fermentation?

A
  • lower temps reaction is too slow
  • high temps the yeast dies and enzymes denature
34
Q

why is fermentation done in an absence of air?

A
  • presence of air can cause extra reactions to occur
  • it oxidises the ethanol produced to ethanoic acid
35
Q

what are the advantages of fermentation?

A
  • sugar is a renewable resource
  • production uses low level tech/ cheap equipment
36
Q

what are the disadvantages of fermentation?

A
  • batch processs which is slow and gives high production costs
  • ethanol made is not pure and needs purifying
  • depletes land for growing crops
37
Q

give the reagent and type of reaction for production of ethene from industry

A

reagent - ethene - from cracking of fractions

reaction - hydration / addition

38
Q

what are the essential conditions for production of ethene from industry

A
  • high temperature at 300*
  • high pressure 70atm
  • strong acidic catalyst of conc H3PO4
39
Q

what are the advantages of ethene from industry?

A
  • faster reaction
  • purer product
  • continuous process
40
Q

what are the disadvantages of production of ethene from industry

A
  • high tech equipment needed
  • expensive
  • high enery costs for pumping to produce high pressures
  • non renewable

A LEVEL CHEM (20 decks)

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