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as level chemistry > 2.7 alcohols and carboxylic acids > Flashcards

2.7 alcohols and carboxylic acids Flashcards

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1
Q

what is the functional group of alcohols?

A

-OH

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2
Q

how can you work out wether an alcohol is primary, secondary or tertiary?

A
  • look at the carbon directly bonded to the -OH group
  • count how many carbons this carbon is bonded to
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3
Q

name:
. H H H
I I I
H - C - C - C - H
I I I
OH OH OH

A

propane-1,2,3-triol

e - bc more than 1 alcohol group

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4
Q

decide whether this alcohol is primary, secondary or tertiary?
. H H H H
I I I I
H - C - C - C - C - H
I I I I
H OH H H

A

secondary

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5
Q

what are the 3 ways of making alcohols?

A
  1. fermentation
  2. from alkenes
  3. from halogenoalkanes
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6
Q

how does making alcohols from fermentation work?

A
  • glucose from the sugar cane plant is converted to ethanol and CO2
  • reaction is carried out between 30-35.C
  • enzyme (zymase) in yeast convert the glucose to the products
  • reaction is carries out in the absence of oxygen (anaerobic conditions) otherwise ethanol is oxidised to vinegar
  • the ethanol is separated from the mixture by filtering and then by distillation to give 96% pure ethanol
  • ethanol produced this way is sometimes referred to as a biofuel (a fuel produced by a biological process)
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7
Q

what is the formula for the reaction of making alcohols from fermentation?

A

C6H12O6 —> 2C2H5OH + 2CO2

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8
Q

what are the conditions for the reaction of making alcohols from fermentation?

A
  • between 30-35°C
  • enzyme (zymase) in yeast
  • anaerobic conditions
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9
Q

why is the reaction of making alcohols from fermentation carried out in anaerobic conditions?

A

otherwise the ethanol is oxidised to vinegar

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10
Q

how is the ethanol separated from the mixture in the reaction of making alcohols from fermentation?

A

by filtering and then by distillation

(con)

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11
Q

what is a biofuel?

A

a fuel produced by a biological process

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12
Q

what are the cons for the reaction of making alcohols from fermentation?

A
  • takes a long time
  • filtering and distillation
  • this process doesnt produce 100% concentrated ethanol as fermentation stops when the concentration of ethanol reaches around 15% bc at these levels enzymes in the yeast cease to function
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13
Q

what are the advantages and disadvantages of biofuels?

A

disadv:
- biofuels release less energy per gram compared to fossil fuels
- more people are required to produce biofuels compared to fossil fuels
- more land is required to be cleared to grow the plants which can lead to deforestation
- not really carbon neutral as dont take into account fuel needed to build factories, transport raw materials etc

adv:
- increased income for farmers
- helps lower fuel prices as biofuels limit the demand for fossil fuels
- renewable
- carbon neutral - bc even tho produce CO2, plants take it in

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14
Q

how can alcohols be made from alkenes?

A

CALLED A HYDRATION/ADDITION REACTION
- steam and ethene are passed over a catalyst of conc sulfuric or phosphoric acid

. H H H H
I I I I
C=C + H2O (g) —> H - C - C - O - H
I I I I
H H H H

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15
Q

what are the conditions for the addition reaction of making alcohols from alkenes?

A
  • 300°C
  • 60-70 atm
  • concentrated sulfuric or phosphoric acid catalyst
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16
Q

what is the name of the reaction of making alcohols from alkenes?

A

addition reaction

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17
Q

what is the name of the reaction of making alcohols from halogenoalkanes?

A

nucleophilic substitution

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18
Q

what are the conditions for nucleophilic substitution (making alcohols from halogenoalkanes)?

A
  • aqueous sodium hydroxide
  • reflux/warm
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19
Q

what does an addition reaction mean?

A

there’s only one overall product

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20
Q

what are the 2 reactions of alcohols?

A
  1. dehydration/elimination
  2. oxidation reactions
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21
Q

what does the dehydration/elimination reaction form?

A

an alkene (from an alcohol)

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22
Q

what is the dehydration/elimination reaction?

A
  • alcohol —> water + alkene
  • dehydrate means to eliminate water
  • if you dehydrate an alcohol, you lose the -OH group and an adjacent (next C over) hydrogen atom to make the eliminated water molecule

. I I I I /
- C - C - C - O - H —> - C - C =C
I I I I I \

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23
Q

what are the conditions for the dehydration/elimination reaction?

A
  • concentrated sulfuric acid
  • 170°C
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24
Q

can this alcohol be dehydrated?
.
I
- C -
I I I
- C - C - C - OH
I I I
- C -
I

A

no because the C adjacent to the C with the OH doesn’t have a H to lose

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25
Q

what happens during the oxidation reaction of alcohols?

A
  • an oxidation reaction can be thought of a molecule that gains an oxygen atom or one that loses hydrogen
  • loss of electrons - can be seen as colour changes in the oxidising agent
  • main oxidising agent for AS is acidified potassium dichromate H+/K2Cr2O7 (sometimes referred to acidified dichromate which is the same reagent but missing out the potassium H+/Cr2O7 2-
  • to make the oxidising agent we add potassium dichromate and sulfuric acid
  • water is always produced
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26
Q

how do you make the oxidising agent in the oxidising reactions of alcohols?

A

add sulfuric acid and potassium dichromate (hence acidified potassium dichromate)

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27
Q

what are the two products that the oxidation reactions of PRIMARY alcohols make? how are they made?

A
  1. aldehydes - partially oxidised using acidified potassium dichromate under reflux (heating) and then distill it out
  2. carboxylic acid - full oxidation by heating under reflux with acidified potassium dichromate (not distilled)
28
Q

what is the colour change from adding acidified potassium dichromate to an alcohol? (TEST FOR ALCOHOLS)

A

from orange to green

29
Q

what are the conditions of the oxidising reaction from alcohols to aldehydes?

A
  • acidified potassium dichromate
  • heat followed by distillation
30
Q

what are the conditions of the oxidising reaction from alcohols to carboxylic acids?

A
  • acidified potassium dichromate
  • reflux
31
Q

if the aldehyde is not distilled out, can the aldehyde be further oxidised to a carboxylic acid?

A

yes

32
Q

aldehyde functional group:

A

. O
//
R - C
\
H

33
Q

carboxylic acid functional group:

A

. O
//
R - C
\
OH

34
Q

what does [O] represent?

A

the oxidising agent (e.g acidified potassium dichromate)

35
Q

what is the product that the oxidation reactions of SECONDARY alcohols made?

A
  • ketones
36
Q

what are the conditions for the oxidising reaction of making ketones?

A
  • acidified potassium dichromate
  • reflux
37
Q

ketone functional group:

A

. O
I II I
- C - C - C -
I I I

38
Q

how are ketones different to aldehydes?

A

as the C=O in ketones are bonded to 2 other carbons
while in aldehydes, the C=O is bonded to 1 other C atom and 1 hydrogen

39
Q

what is the name endings for aldehydes?

A
  • al

(e.g ethanal)

40
Q

what is the name endings for ketones?

A
  • one (own)

e.g butan-2-one

41
Q

how do you test for primary and secondary alcohols?

A

add acidified potassium dichromate under reflux

orange —> green

(doesnt work for tertiary alcohols)

42
Q

why can’t you test for tertiary alcohols using APD?

A

(for the scope of A level, tertiary alcohols are resistant to oxidation)

so adding acidified potassium dichromate under reflux has NO EFFECT

43
Q

what is the name ending for a carboxylic acid?

A

-oic acid

e.g ethanoic acid

44
Q

what are the 2 ways of testing for a carboxylic acid?

A
  1. add a carbonate
  2. add a hydrogencarbonate
45
Q

how does the test for carboxylic acids bu adding a carbonate work?

A
  • add a carbonate (e.g sodium carbonate)
  • this produced bubbles/effervescence (of carbon dioxide gas)
46
Q

how does the test for carboxylic acids by adding a hydrogencarbonate work?

A
  • add a hydrogencarbonate (e.g sodium hydrogencarbonate NaHCO3)
  • this produces bubbles/effervescence (of carbon dioxide gas)
47
Q

what is seen when carboxylic acids are reacted with bases?

A

no VISIBLE reaction is seen

48
Q

what is the formula and charge of a hydrogencarbonate?

A

HCO3 -

49
Q

how are esters formed?

A

from reactions of carboxylic acids with alcohols

  • the carboxylic acid loses an -OH group and the alcohol loses a H. this combines to make wager as a by-product
50
Q

what is the type of reaction that occurs between alcohols and carboxylic acids called?

A

esterification
(opposite of hydrolysis)

51
Q

what are esters described as?

A

sweet smelling compounds

52
Q

is esterification reversible?

A

yes
so le chatelier applies

53
Q

what are the conditions for esterification?

A
  • concentrated H2SO4 or concentrated HCl catalyst
  • reflux
54
Q

in order to increase the yield of ester in esterification, what can you do?

A

remove the water produced
so equilibrium shifts to replace it so increases yield of ester

55
Q

how do you name esters?

A
  • name the section that came originally from the alcohol first, then the bit that came from the carboxylic acid
  • esters end in -oate
56
Q

name the ester:
. O
II
C CH3
/ \ /
H3C O

A

methylethanoate

57
Q

what is the general formula of alcohols?

A

CnH2n+1OH

58
Q

how do you name alcohols if the -OH group is not the main functional group in the chain?

A

it is referred to as a ‘hydroxyl-‘ group

e.g 2-hydroxybutanoic acid

59
Q

are smaller chain alcohols miscible (mixes with water easily)?

A

yes due to their ability to hydrogen bond with water molecules

60
Q

what are some uses of alcohols?

A
  • ethanol has been used as the active ingredient in alcoholic drinks
  • ethanol is used as a biofuel and used as a petrol substitute in countries where oil supplies are low
61
Q

what are the results of primary, secondary and tertiary alcohols with litmus paper?

A

primary - blue to red
secondary - remains blue
tertiary - remains blue

62
Q

explain how ethanol can be separated from water?

A

ethanol and water have different boiling points so they can be separated by distillation
- the mixture is heated until the ethanol evaporates
- the ethanol vapour enter the condenser where they condense and run into a beaker

63
Q

in an industrial process where the forwards reaction is exothermic, so a high yield would be favoured by a low temperature, why isnt a low temperature used?

A

as this would give a slow rate of reaction, so a compromised temperature is used

64
Q

in an industrial process where a high yield is favoured by a high pressure, why isnt a high pressure used?

A

as a too high pressure is expensive to maintain

65
Q

are carboxylic acids strong or weak?

A

they are weak acids

66
Q

carboxylic acid + alcohol ⇌

A

ester + water

67
Q

alcohols react with carboxylic acids to form esters.
a method used to separate the product from the liquid mixture is distillation.
state which property of an ester allows this method of separation to be used? [1]

A

the boiling temperature of ester is lower than alcohol/acid

as level chemistry (16 decks)

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