Chapter 14 - alcohols Flashcards
define what an alcohol is
alcohols are organic compounds where a hydrogen atom of an alkane has been replaced with the OH hydroxyl group
what is the general formula for an alcohol
CnH2n+1OH
what is a -diol suffix
where there is more than one alcohol group
what are the key physical properties of alcohols
- bpt higher relative to their comparative alkanes
- less volatile
- more soluble
- these differences lessen with chain length
why do these bpt differences occur
alkanes have only non-polar bonds, therefore the only intermolecular forces are weak London forces
alcohols contain a polar O-H bond where the oxygen has lone pairs
this allows hydrogen bonding to occur in alcohols
more energy is required to overcome these intermolecular forces
why are alcohols sometimes water soluble
- a compound which forms hydrogen bonds is more water soluble than one which doesn’t
- this is because they disrupt the hydrogen bonding of the water
- they also form hydrogen bonds to many of the water molecules
what is the trend in solubility of alcohols and why
- as chain length increases, solubility decreases because the influence of the -OH (hydrogen bonding part of the molecule) decreases in comparison to molecule size
what is a primary, secondary, tertiary alcohol
- a primary alcohol has the -OH group attached to a carbon only attached to one other carbon
- a secondary alcohol has the -OH group attached to a carbon with 2 alkyl groups
- a tertiary alcohol has the -OH group attached to a carbon attached to 3 alkyl groups
do alcohols combust
yes
write the equation for the complete combustion of ethanol
C2H5OH + 3O2 —> 2CO2 + 3H2O
what is required for the oxidation of alcohols and what is the observed colour change
acidified potassium dichromate is required
K2Cr2O7/H2SO4
or just dichromate ions in acid
Cr2O7^2+/H+
the observed colour change is orange to green as chromate ions go into solution
what is a distillation setup
where the conical/round bottomed flask has a tube going up to a thermometer then a diagonal liebig condenser leading to a beaker
what is the purpose of the distillation setup
it drains off the product before further reaction takes place
what is the reflux setup
it is where the round bottomed flask leads straight into a liebig condenser
what is the purpose of a reflux setup
it is used for heating things strongly in order for multiple reactions to happen - think screaming man
and to prevent reactants from escaping
what occurs when a primary alcohol is oxidised under distillation
an aldehyde is formed
the aldehyde is distilled out to stop it further oxidising
write the equation for the oxidation of butan-1-ol to butanal
and conditions
C4H9OH + [O] —> C4H7HO + H2O
with K2Cr2O7/H2SO4
distillation
what occurs when a primary alcohol is oxidised under reflux
it forms first an aldehyde then a carboxylic acid
write the equation for the oxidation of butan-1-ol to butanal and the equation for the oxidation of butanal to butanoic acid, and write the overall equation
butan-1-ol to butanal
C4H9OH + [O] —> C4H7HO + H2O
butanal to butanoic acid
C4H7HO + [O] —> C3H7COOH
overall equation
C4H9OH + 2[O] —> C3H7COOH + H2O
what happens when a secondary alcohol oxidises
and what are the reactants and conditions
a ketone is formed
acidified dichromate ions are needed and under reflux
write the equation for butan-2-ol to butanone
C4H9OH + [O] —> C4H8O + H2O
what is a way to tell the difference between a ketone and an aldehyde
add acidified potassium dichromate, the aldehyde will further oxidise forming a carboxylic acid and changing colour from orange to green
the ketone won’t
do tertiary alcohols oxidise
No
what other reactant is required for the dehydration of alcohols
concentrated sulphuric acid
concentrated phosphoric acid
what is formed when an alcohol is dehydrated
an alkene and water
what occurs when a hydrogen halide reacts with an alcohol
a substitution reaction occurs where the halide replaces the OH group and a haloalkane is formed
what is needed for the substitution reaction of alcohols to haloalkanes occur
sulphuric acid and a sodium halide
these then form a hydrogen halide and NaHSO4
what are the two main ways of producing alcohol (ethanol)
state the conditions
- hydration of ethene, steam and a phosphoric acid catalyst are required
- fermentation of glucose, anaerobic, warm (25-40C) aqueous
how do you know when fermentation is complete
there will be no more CO2 bubbles
what are the energy requirements of these two main ways of forming ethanol
- energy is required for producing steam and fractional distillation for ethene
- energy is required for heating the fermentation mixture and distilling after
