alcohols Flashcards
general formula for alcohol
CnH2n+1OH
intermolecular forces in alcohols
hydrogen bonding due to OH bond
how do alcohols mp and bp compare with hydrocarbons’ of similar C chain lengths
higher because of hydrogen bonding compared to van der waals
are alcohols soluble in water? why does solubility depend on chain length?
soluble short chain
insoluble long chain
OH hydrogen bonds with water, but in long chains non-polarity takes precedence
primary alcohol
C bonded to OH is only bonded to one other C atom
what makes an alcohol secondary
C bonded to OH 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
(phosphoric acid catalyst H3PO4)
advantages and disadvantages of making ethanol from crude oil
advantages:
fast, continuous process, ethanol has high purity
disadvantages:
not renewable as from crude oil
how can ethanol be made from fermentation
plant carbohydrates broken down and fermented by enzymes in yeast –> ethanol
what conditions are needed for this reaction to take place
enzymes in yeast as a catalyst
35 degrees C
anaerobic conditions
equation for reaction which takes place
C6H12O6 (aq) –> 2C2H5OH + 2CO2
what are the advantages and disadvantages of ethanol from fermentation
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
in the future, how might most ethene be made? why is it not made like this at the moment
dehydrate ethanol made by fermentation –> ethene
not economical at the moment
define carbon neutral
no net addition of CO2 to the atmosphere - COs released when combusted = CO2 absorbed as a plant
explain how using ethanol in petrol engines could be considered to be carbon neutral
CO2 released in fermentation and combustion = CO2 absorbed when growing
why would it probably not be entirely carbon neutral to use ethanol in petrol engines
other carbon costs such as transport
what is a commercial fuel that uses ethanol and what does it contain and why
methylated spirits contains methanol which is toxic so can’t be drunk
write an equation for combustion of ethanol
C2H5OH (l) + 3O2 (g) –> 2CO2 (g) + 3H2O (l)
what is an elimination reaction
removal of a smaller molecule from a larger one
which groups leaves the parent molecule in the case of alcohols
OH and a H (to form water)
what physical conditions are needed for the elimination reaction from alcohols to alkenes
excess hot concentrated sulphuric acid
OR
pass 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 (VI), distill product as its produced, gentle heating
equation for partial oxidation of ethanol
CH3CH2OH (l) + [O] –> CH3CHO (g) + H2O (l)
what forms if you fully oxidise a primary alcohol
carboxylic acid
what conditions are needed for this reaction
concentrated sulphuric acid, potassium dichromate (VI), reflux for about 20 mins, strong heating
write an equation for full oxidation of ethanol
CH3CH2OH (l) + 2[O] –> CH3COOH (g) + H2O (l)
what forms if you oxidise a secondary alcohol
ketone
why can a ketone not be oxidised further? why can’t a tertiary alcohol be oxidised?
carbon-carbon bond would have to break
what conditions are needed for the oxidation of a secondary alcohol
concentrated sulphuric acid,
potassium dichromate (VI),
reflux for about 20 mins,
strong heating
write an equation for the oxidation of propan-2-ol
CH3CH(OH)CH3 (l) + [O] –> CH3COCH3 (g) + H2O (l)
what is an aldehyde and what is its functional group
molecule with C=O group at end of carbon chain
suffix for aldehyde
-al
what is a ketone
molecule with C=O in middle of carbon chain
suffix for ketone
-one
what is a carboxylic acid
molecule with COOH at end of carbon chain
suffix for carboxylic acid
-oic acid
what does Tollens’ test give positive result for
aldehydes
what is in tollens reagent and how does it react with substance tested
silver nitrate in NH3 (aq)
oxidises aldehydes but not ketones
complex silver (I) ions reduced to Ag (s) giving silver mirror
how do you carry out Tollens test
equal volumes of substance being tested and tollens reagent to a test tube and leave in water bath to observe changes
result of the Tollen’s test for aldehydes and ketones
aldehydes = silver mirror
ketones = no visible change
what does Fehlings solution give +ve test for
aldehydes
what is Fehlings
blue copper (II) complex ions - gentle oxidising agent
reduced to Cu+ ions (brick red)
what conditions do you need to use the Fehling’s solution
heat
what result do aldehydes and ketones give in Fehlings
aldehyde = brick red
ketone = no visible change
