3.3.5 Alcohols
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what is the functional group of an alcohol?
R-OH
what is the functional group of a diol?
OH-R-OH
what is the general formula of an alcohol?
CnH2n+1OH
what type of intermolecular forces do alcohols have? why?
hydrogen bonding - H directly bonded to O, difference in electronegativity
how do alcohols’ mp and bp compare to other hydrocarbons with the same chain lengths? why?
higher, because they have hydrogen bonding —> stronger than VdW
are alcohols soluble in water? why does solubility depend on chain length?
soluble when short chain - OH hydrogen bonds to hydrogen bond to water insoluble when long chain - non polarity of C-H bond takes precedence.
what makes an alcohol primary?
C bonded to OH is only bonded to one other carbon atom
what makes an alcohol secondary?
C bonded to OH is bonded to 2 other C atoms
what makes an alcohol tertiary?
C bonded to OH is bonded to three other C atoms
how can ethanol be made from crude oil?
hydration of ethene via electrophilic addition
what are the advantages and disadvantages of production of ethanol from crude oil?
advantages - fast, continuous process, ethanol has a high purity disadvantages - not renewable as from crude oil
how can ethanol be made by fermentation?
plant carbohydrates broken down and fermented by enzymes in yeast —> ethanol
what conditions are needed for the fermentation to form ethanol?
enzymes in yeast act as a catalyst 35 degrees anaerobic conditions
write an equation for the fermentation of plant carbohydrates to form ethanol.
C6H12O6(aq) —> 2C2H5OH + 2CO2
what are the advantages disadvantages of fermentation of plant carbohydrates to form ethanol?
advantages - renewable as from plants disadvantages - slow, batch process, enzymes stop working at 15% alcohol so solution is not pure, needed to be fractionally distilled
define carbon neutral
no net addition of CO2 to the atmosphere - CO2 released when combusted = CO2 absorbed as a plant
why would it probably not be entirely carbon neutral to use ethanol?
other “carbon costs” associated with it eg. transport
write an equation for the combustion of ethanol.
C2H6O + 3O2 —> 2CO2 + 3H2O
what is an elimination reaction?
removal of a smaller molecule from a larger one
what leaves the parent molecule when it comes to alcohols?
OH and H (to form water)
what physical conditions are needed for the elimination reaction from alcohols to alkenes?
excess hot conc sulphuric acid or pass hot vapour over hot aluminium oxide.
what forms if you partially oxidise a primary alcohol?
an aldehyde
what conditions are needed to partially oxidise a primary alcohol?
dilute sulphuric acid, potassium dichromate, distill product as it’s produced, gentle heating
write an equation for the partial oxidation of ethanol.
C2H6O + [O] —> C2H4O + H2O