Chapter 14 - alcohols

Question 1

define what an alcohol is

Answer 1

alcohols are organic compounds where a hydrogen atom of an alkane has been replaced with the OH hydroxyl group

Question 2

what is the general formula for an alcohol

Answer 2

CnH2n+1OH

Question 3

what is a -diol suffix

Answer 3

where there is more than one alcohol group

Question 4

what are the key physical properties of alcohols

Answer 4

• bpt higher relative to their comparative alkanes
• less volatile
• more soluble
• these differences lessen with chain length

Question 5

why do these bpt differences occur

Answer 5

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

Question 6

why are alcohols sometimes water soluble

Answer 6

• 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

Question 7

what is the trend in solubility of alcohols and why

Answer 7

• as chain length increases, solubility decreases because the influence of the -OH (hydrogen bonding part of the molecule) decreases in comparison to molecule size

Question 8

what is a primary, secondary, tertiary alcohol

Answer 8

• 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

Question 9

do alcohols combust

Answer 9

yes

Question 10

write the equation for the complete combustion of ethanol

Answer 10

C2H5OH + 3O2 —> 2CO2 + 3H2O

Question 11

what is required for the oxidation of alcohols and what is the observed colour change

Answer 11

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

Question 12

what is a distillation setup

Answer 12

where the conical/round bottomed flask has a tube going up to a thermometer then a diagonal liebig condenser leading to a beaker

Question 13

what is the purpose of the distillation setup

Answer 13

it drains off the product before further reaction takes place

Question 14

what is the reflux setup

Answer 14

it is where the round bottomed flask leads straight into a liebig condenser

Question 15

what is the purpose of a reflux setup

Answer 15

it is used for heating things strongly in order for multiple reactions to happen - think screaming man
and to prevent reactants from escaping

Question 16

what occurs when a primary alcohol is oxidised under distillation

Answer 16

an aldehyde is formed

the aldehyde is distilled out to stop it further oxidising

Question 17

write the equation for the oxidation of butan-1-ol to butanal
and conditions

Answer 17

C4H9OH + [O] —> C4H7HO + H2O
with K2Cr2O7/H2SO4
distillation

Question 18

what occurs when a primary alcohol is oxidised under reflux

Answer 18

it forms first an aldehyde then a carboxylic acid

Question 19

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

Answer 19

butan-1-ol to butanal
C4H9OH + [O] —> C4H7HO + H2O

butanal to butanoic acid
C4H7HO + [O] —> C3H7COOH

overall equation
C4H9OH + 2[O] —> C3H7COOH + H2O

Question 20

what happens when a secondary alcohol oxidises

and what are the reactants and conditions

Answer 20

a ketone is formed

acidified dichromate ions are needed and under reflux

Question 21

write the equation for butan-2-ol to butanone

Answer 21

C4H9OH + [O] —> C4H8O + H2O

Question 22

what is a way to tell the difference between a ketone and an aldehyde

Answer 22

add acidified potassium dichromate, the aldehyde will further oxidise forming a carboxylic acid and changing colour from orange to green
the ketone won’t

Question 23

do tertiary alcohols oxidise

Answer 23

No

Question 24

what other reactant is required for the dehydration of alcohols

Answer 24

concentrated sulphuric acid

concentrated phosphoric acid

Question 25

what is formed when an alcohol is dehydrated

Answer 25

an alkene and water

Question 26

what occurs when a hydrogen halide reacts with an alcohol

Answer 26

a substitution reaction occurs where the halide replaces the OH group and a haloalkane is formed

Question 27

what is needed for the substitution reaction of alcohols to haloalkanes occur

Answer 27

sulphuric acid and a sodium halide

these then form a hydrogen halide and NaHSO4

Question 28

what are the two main ways of producing alcohol (ethanol)

state the conditions

Answer 28

• hydration of ethene, steam and a phosphoric acid catalyst are required
• fermentation of glucose, anaerobic, warm (25-40C) aqueous

Question 29

how do you know when fermentation is complete

Answer 29

there will be no more CO2 bubbles

Question 30

what are the energy requirements of these two main ways of forming ethanol

Answer 30

• energy is required for producing steam and fractional distillation for ethene
• energy is required for heating the fermentation mixture and distilling after