3.5- alcohols Flashcards
general formula
CnH2n+1OH
why does ethanol have a higher BP than propanone (2)
-propanone= VDW
-ehtanol= H-bonding which is stronger
trend in solubility down group (3)
-decreases
-number of carbons in a chain increases
-chain gets longer+non-polar and only the -OH bond can form H-bonds
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direct hydration equation
C2H4 + H2O(g) –> C2H5OH
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direct hydration conditions (3)
concentrated phosphoric acid catalyst
300°C
65atm
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2 advantages of direct hydration
-faster reaction
-purer product (95% ethanol)
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2 disadvantages of direct hydration
-raw material (crude oil) is non renewable
-high energy costs for high temp and pressures
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equation for anaerobic fermentation
C6H12O6(aq) –> 2CH3CH2OH(aq) + 2CO2(g)
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conditions for anaerobic fermentation (4)
-anaerobic
-yeast
-aqueous
-35°C
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why does anaerobic fermentation have to be anaerobic (2)
-prevent O2 entering, which would oxidise ethanol into a carboxylic acid
-air may contain pathogens which can grow in the mixture and make toxins
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why is the temperature what it is for anaerobic fermentation (2)
-higher temp= enzymes denature
-lower temp= slower reaction
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why is yeast needed for anaerobic fermentation
provides enzymes (biological catalysts)
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anaerobic fermentation- what are the 3 processes and their equations
process 1- photosynthesis
6CO2 + 6H2O –> C6H12O6 + 6O2
process 2- fermentation of glucose
C6H12O6 –> 2CH3CH2OH + 2CO2
process 3- complete combustion of ethanol
2CH3CH2OH + 6O2 –> 4CO2 +6H2O
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why is the process for anaerobic fermentation claimed to be carbon neutral
6CO2 used in process 1, 6CO2 produced in process 2 and 3
carbon neutral definition
no net emissions of CO2 into atmosphere
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why is anaerobic fermentation not carbon neutral (2 )
-lots of CO2 used+emitted during manufacturing the process (transport+machinery)
-fractional distillation needed to separate ethanol which needs lots of energy
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advantage of anaerobic fermentation
renewable raw materials (glucose from sugar cane)
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2 disadvantages of anaerobic fermentation
-slower reaction
-impure product (10% ethanol)
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how to purify ethanol in anaerobic fermentation (2)
-filter out the yeast
-separate water+ethanol with fractional distillation
reagent for oxidising alcohols
warm solution of acidified potassium dichromate (acidified with dilute H2SO4)
colour change for oxidising alochols
orange solution –> green solution
Cr2O72- ions get reduced to Cr3+
what do primary alcohols oxidise into
aldehydes
has a lower BP than primary alcohol so can be distilled off
what do aldehydes oxidise into
carboxylic acids
if alcohol is heated under reflux, aldehyde doesnt evaporate and gets further oxidised into carboxylic acids
what do secondary alcohols oxidise into
ketones
under reflux
