Alcohols

Question 1

Physical properties of alcohols

Answer 1

Greater boiling points than alkanes with similar Mr
Presence of hydrogen bonds between alcohol
OH group makes soluble
Solubility decreases with increasing chain length

Question 2

Alcohol classification

Answer 2

Primary- one alkyl group on C-OH
Secondsry- two alkyl groups on C-OH
Tertiary- three alkyl groups on C-OH

Question 3

Oxidation reactions with alcohols

Answer 3

Primary alcohols-> aldehyde -> carboxylic acid
Carboxylic acids obtained through reflux the removed via distillation
Aldehyde obtained by distillation
Secondary alcohols -> ketone
Tertiary alcohols cannot be oxidised
Oxidising agent-> acidified potassium dichromate
Colours change orange to green

Question 5

Test for aldehyde and ketone

Answer 5

Tollens reagant (silver mirror test)
[Ag(NH3)2]+ mild oxidising agents
Warmed with solution
Ag+(aq) + e- -> Ag(s) forming a silver mirror
Feelings solution
Cu2+ +e- -> Cu+ blue solution to red precipitate
Positive for aldehyde negative for ketone

Question 6

Elimination reactions of alcohols

Answer 6

Dehydration reaction removing water
Concentrated sulfuric acid catalyst
170°C
Sulfuric acid reacts first to form carbocation intermediate
Water reacts next to form alkene

Question 7

Elimination of unsymmetrical alcohols

Answer 7

Forms three possible products
2 E-Z isomers and one unsymmetrical alkene

Question 8

Fermentation

Answer 8

C6H12O6 -> 2C2H5OH + 2CO2
Yeast catalyst
Anaerobic
35-40°C
Yeast killed by concentration of ethanol above 14%
Makes biofuel

Question 9

Hydration ethene

Answer 9

C2H4 + H2O <=> C2H5OH
Phosphoric acid concentrated catalyst
60 atmosphere
600K
Excess ethene

Question 10

Compare fermentation and hydration for ethanol production

Answer 10

Fermentation: batch process (inefficient), very slow, impure product, gentle temperatures and pressure, uses renewable resources
Hydration: continuous process, very fast, purer ethanol, high temperatures and pressures, finite resources from crude oil

Question 11

Is bioethanol carbon neutral

Answer 11

Photosynthesis:6CO2 + 6H2O -> C6H12O6 +6O2
Fermentation: C6H12O6 -> 2C2H5OH + 2CO2
Combustion for fuel: 2C2H5OH2 + 6O2 -> 4CO2 + 6H2O
6CO2 absorbed and 6CO2 released
However energy needed for each process is most likely supplied by combustion of fossil fuels
Fertilisers and pesticides for crops require energy to be manufactured
Ethanol has to be extracted from mixture
Must be transported to fuel pumps
So in reality is not carbon neutral

Question 12

What are disadvantages to using plants for biofuel

Answer 12

Food depletion as less space for food crops
Production reliant on weather and climate
Time consuming
Produces a mixture requiring seperation