3.3.5 Alcohols Flashcards
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
what forms if you fully oxidise a primary alcohol?
a carboxylic acid
what conditions are needed to fully oxidise a primary alcohol?
conc. sulphuric acid, potassium dichromate, reflux for about 20 minutes, strong heating
write an equation for the full oxidation of ethanol.
C2H6O + 2[O] —> CH3COOH + H2O
what forms if you oxidise a secondary alcohol?
a ketone
why can’t a secondary alcohol be oxidised further than a ketone? why can’t a tertiary alcohol be oxidised?
a carbon- carbon bond would have to break
what conditions are needed for the oxidation of a secondary alcohol?
conc sulphuric acid, potassium dichromate, reflux for around 20 mins, strong heating
write an equation for the oxidation of propan-2-ol.
C3H8O + [O] —> CH3COCH3 + H2O
what does the Tollens’ test give a positive result for?
aldehydes
what is in Tollens’ reagent? how does this react with the substance it is testing for?
silver nitrate in NH3(aq) - oxidises aldehydes but not ketones
complex silver (I) reduced to Ag(s)
how do you carry out the Tollens’ test?
add equal volumes of substance being tested and Tollens’ reagent to a test tube, leave in water bath for 10 mins and observe any changes
what is the result of the Tollens’ test for aldehydes and ketones?
aldehydes - silver mirror (solid Ag)
ketones - no visible change
What does Fehling’s sol. give a positive test for?
aldehydes
What is in Fehling’s? how does this react with the substance to be tested?
Blue copper (II) complex ions - gentle oxidising agent
Reduced to Cu2+ ions (brick red)
what conditions are needed to use Fehling’s sol?
heat
what result do aldehydes and ketones give in the Fehling’s test?
aldehydes - brick red ppt.
ketones - no visible change
