5-O Alcohols

Question 1

What’s the general formula for an alcohol

Answer 1

CnH2n+1OH

Question 2

When molecules have more than one functional group what is the priority order with prefix

Answer 2

1-Carboxylic acid (no prefix only suffix highest priority)
2-nitrile (cyano) use number to indicate position for rest
3-aldehyde (oxo)
4-ketone (oxo)
5-alcohol (hydroxy)
6-amine (amino)

Question 3

How to name an alcohol with 1 -OH group

Answer 3

Alkane name, remove e, count which carbon atom it’s connected to (lowest number) then add ol
eg ethanol
eg butan-1-ol

Question 4

How to make an alcohol with 2 or more -OH groups

Answer 4

Alkane name, add the numbers to which carbon atoms the -OH groups are attached to (lowest numbers), add di, tri, tetra etc, add ol

eg butane-1,4-diol

Question 5

What’s the reactants/product of hydration and the catalyst

Answer 5

Reactant is an alkene and water (g)
Product is an alcohol
H3PO4 catalyst

Question 6

How is ethanol made from fermentation

Answer 6

Carbohydrates from plants broken down into sugar by enzymes from yeast then converted into ethanol

Question 7

Equation for production of ethanol by fermentation and fractional distillation give conditions for each

Answer 7

C6H12O6(aq) —> 2C2H5OH(aq) +2CO2(g)
Anaerobic conditions, prevent ethanol forming ethanoic acid
Compromised temp 35°, enzymes made ineffective at high temps
Yeast catalyst
Solution needs to be aqueous

15% yield of ethanol is then fractionally distilled as it has a boiling point lower than water

Question 8

What’s a biofuel

Answer 8

A fuel derived or produced from renewable and biological sources

Question 9

Evaluate whether ethanol produced by fermentation is carbon neutral

Answer 9

Agree
(Photosynthesis) 6CO2 + 6H2O —> C6H12O6 + 6O2

(Fermentation) C6H12O6 —> 2C2H5OH + 2CO2
(Combustion) 2C2H5OH + 6O2 —> 4CO2 +6H2O
6 mol of CO2 absorbed 6mol of CO2 released, not net emissions

Disagree
Energy needed for transport of fuel and processing it is from fossil fuels
Fertiliser required contains carbon

Question 10

Mechanism for hydration of alkenes is in alkene deck

Question 11

What are environmental and ethical issues surrounding biofuel use

Answer 11

Land used to grow plants could be used to grow food

Question 12

How to know if an alcohol is tertiary/3°

Answer 12

The substitute group is on the same C atom as the -OH group

Question 13

What are 1°, 2°, 3° alcohols

Answer 13

1°, 1 alkyl group attached to carbon with -OH
2°, 2 alkyl groups attached to carbon with -OH
3°, 3 alkyl groups attached to carbon with -OH

Question 14

What can primary alcohols eg ethanol be oxidised into

Answer 14

Aldehydes, further oxidised into carboxylic acids

1) CH3CH2OH +[O] —> CH3CHO+ H2O
2)CH3CH2OH + 2[O] —> CH3COOH + H2O

Question 15

How are the methods to produces aldehydes or carboxylic acids from primary alcohols different

Answer 15

Aldehydes
[O] and excess alcohol added into hot acid
Aldehyde distilled off to prevent further oxidation

Carboxylic acids
Heat under reflux, distill off products
Excess [O]

Question 16

What are secondary alcohols eg propan-2-ol oxidised to

Answer 16

Ketone
CH3CH(CH3)OH + [O] —> CH3COCH3 + H2O

Question 17

What’s the oxidising agent used to oxidise alcohols

Answer 17

Acidified Potassium dichromate (VI)
Orange solution turns green in presence of primary/secondary alcohol

Question 18

What happens in oxidation in terms of hydrogen

Answer 18

Loses hydrogen

Question 19

Ionic equation for reaction of ethanol with acidified dichromate

Answer 19

6ē +14H+ + Cr2O7 2- —> 2Cr 3+ + 7H2O

Question 20

Half equation for reaction of ethanol to give ethanal

Answer 20

CH3CH2OH —> CH3CHO + 2H+ + 2ē

Question 21

Half equation for reaction of ethanol to ethanoic acid

Answer 21

CH3CH2OH + H2O —> CH3COOH + 4H+ + 4ē

Question 22

How to test for an aldehyde or ketone with fehlings reagent

Answer 22

Aldehyde, blue solution forms a brick red precipitate

Ketone, solution remains blue

Question 23

How to test for an aldehyde or ketone with tollens reagent

Answer 23

Aldehyde, colourless solutions forms a silver mirror

Ketone, solution remains colourless

Question 24

What reaction turns alcohols into alkenes

Answer 24

Elimination

Question 25

Conditions for an elimination reaction

Answer 25

Heat at 180°c
Excess H2SO4 (catalyst)

Question 26

Uses for elimination reactions

Answer 26

Alkenes produced can form additions polymers without the monomer being derived from crude oil

Question 27

Elimination mechanism on symmetrical alcohols

Answer 27

First arrow: lone pair on the oxygen from the hydroxyl group. The arrow goes from the middle of the lone pair to the H+ catalyst

Second arrow: the oxygen is now bonded to 2 H atoms giving it a +ve charge. The arrow goes from the middle of the carbon oxygen bond onto the oxygen.

third arrow: the C atom has a +ve charge arrow from the middle of the CH bond to the middle of the CC bond.

Question 28

Elimination mechanism for unsymmetrical alcohols

Answer 28

First arrow: lone pair on the oxygen from the hydroxyl group. The arrow goes from the middle of the lone pair to the H+ catalyst

Second arrow: the oxygen is now bonded to 2 H atoms giving it a +ve charge. The arrow goes from the middle of the carbon oxygen bond onto the oxygen.

third arrow: the C atom has a +ve charge arrow from the middle of the CH bond to the middle of the CC bond, two possible products, form E-Z isomers

Question 29

Ethanol production by hydration vs fermentation

Answer 29

Hydration
Higher yield
Ethene is non renewable
Equipment is expensive

Fermentation
Glucose is renewable
Cheaper equipment