Alcohols
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What conditions are required for the fermentation of ethanol?
• yeast • absence of oxygen • 30-40°C
What are 2 ways can ethanol be produced?
• fermentation • hydration of ethene
In what way is ethanol production considered carbon neutral?
There is no net production of carbon
What is formed when a primary alcohol is oxidised?
• an aldehyde (distillation) • then further into a carboxylic acid (reflux)
What product is formed after oxidising a secondary alcohol?
a ketone
What type of reaction is the dehydration of alcohols?
an elimination reaction
What is a common oxidising agent for the oxidation of alcohols?
acidified potassium dichromate
Why can alcohols form hydrogen bonds? How does this impact their properties?
• the O-H bond is polar due to the electronegativity of the oxygen atom • alcohols can form hydrogen bonds with each other and with water • this explains why they are soluble
Why are longer chain alcohols not soluble in water?
The longer chain length means the non-polar hydrocarbon chain dominates and therefore the effect of the H bond has little effect on the molecules properties
What does the term ‘volatility’ mean?
How easily something evaporates
Why might ethanol made by fermentation NOT be considered carbon neutral?
No transport or processing (of the crops) is taken into account, which have C emissions
Give the equations that can be used to argue that using ethanol as a fuel is carbon neutral
6CO2 + 6H2O –> 6O2 + C6H12O6 takes in 6CO2 C6H12O6 –> 2CO2 + 2C2H5OH 2 [C2H5OH –> 2CO2 + 3H2O] in total 6 CO2 are released
What reaction can produce alcohols? (include reaction conditions in answer)
• hydration, • (phosphoric) acid catalyst in aqueous conditions • high temperatures (300C) and pressures (60atm)
How is dehydration carried out?
excess of hot sulfuric acid and Al2O3 as a catalyst
How can H2SO4 be used to form an alcohol?
form an alkyl hydrogen sulfate (electrophilic addition), reacted with water (elimination) forms and alcohol
What does the dehydration of alcohols form?
alkene
What colour change happens when alcohols are oxidised by potassium dichromate?
orange to green
What side products does the dehydration of an alkene using H2SO4 produce?
CO2 SO2