alcohols [O1] PAPER 2

Question 1

what is the functional group of an alcohol?

Answer 1

-OH

Question 2

outline the reaction, conditions and reagent used to form a carboxylic acid from the oxidation of an alcohol

Answer 2

• 1° alcohol + 2[O] -> carboxylic acid + water
• conditions: under reflux
• reagent: acidified potassium dichromate (VI)
e.g.

Question 3

outline the reaction and conditions for the formation of a ketone from an alcohol

Answer 3

• 2° alcohol + [O] -> ketone + water
• acidified potassium dichromate (VI)
• reflux
e.g.

Question 4

can a tertiary alcohol undergo oxidation?

Answer 4

no

Question 5

list the following in order of boiling points, from highest to lowest, and justify this order in terms of intermolecular forces: propan-1-ol, propanal, butane

Answer 5

• propan-1-ol, propanal, butane
• propan-1-ol has hydrogen bonding between molecules
• propanal has dipole-dipole (and vdW) forces between molecules
• butane only has van der Waals forces between molecules
• hydrogen bonding is the strongest intermolecular force, followed by dipole-dipole forces, then van der Waals forces

Question 6

fermentation conditions and equation?

Answer 6

• 35°C
• anaerobic
• (enzymes from) yeast / zymase

Question 7

In industry, this fermentation reaction is carried out at 35°C rather than 25°C.
Suggest one advantage and one disadvantage for industry of carrying out the fermentation at this higher temperature.

Answer 7

• advantage – ethanol is produced at a faster rate
• disadvantage – more energy is used / required in the reaction

Question 8

Ethanol is formed by the fermentation of glucose.
A student carried out this fermentation reaction in a beaker using an aqueous solution of glucose at a temperature of 25°C in the presence of yeast.
The method used by the student would result in the ethanol being contaminated by ethanoic acid.
How does this contamination occur?

Answer 8

Air gets in / oxidation occurs

Question 9

State the meaning of the term carbon-neutral

Answer 9

no net / overall carbon dioxide emissions to the atmosphere

Question 10

A dilute aqueous solution of ethanol can be produced by the fermentation of an aqueous solution of glucose.

(a) give two other essential conditions for this reaction to produce a good yield of ethanol.

(b) name a process used to produce a much more concentrated solution of ethanol from a dilute aqueous solution.

Answer 10

(a) • (enzymes from) yeast / zymase
• 35°C
• anaerobic / no oxygen / no air

(b) fractional distillation

Question 11

state the meaning of the term “hydration”

Answer 11

addition of water

Question 12

Give one advantage and one disadvantage of manufacturing ethanol by fermentation rather than by hydration.

Answer 12

advantages:
• low technology
• renewable resource
• allowed for use in drinks and perfumes
• considered to be green
• can occur at lower temperatures, so less energy required (so cheaper)

disadvantages:
• slower
• lower yield
• significant land use
• has to be distilled
• labour intensive

Question 13

Reagent, conditions and mechanism for the dehydration of an alcohol to form an alkene?

Answer 13

• conc. sulfuric/phosphoric acid
• hot
• elimination

a mixture of alkenes can be formed depending on the alcohol (different carbocations)

Question 14

Give one advantage of using ethanol as a fuel compared with using a petroleum fraction.

Answer 14

sugar/glucose/ethanol is renewable

Question 15

Give a suitable reagent and reaction conditions for the oxidation of ethanol to form the carboxylic acid as the major product

Answer 15

• reagent - potassium dichromate (VI)
• conditions - acidified/sulfuric acid

Question 16

what can alkenes formed through the dehydration of alcohols be used for?

Answer 16

form addition polymers without having to use monomers derived from crude oil

Question 17

what is the role of potassium dichromate (VI) in the oxidation of alcohols?

Answer 17

• oxidising agent
• it is reduced as the alcohol oxidises (so goes from orange to green)

Question 18

name the reaction, conditions and outline the mechanism to form an alcohol from an alkene

Answer 18

• electrophilic addition (hydration too)
• alkene + steam -> alcohol
• conc. H2SO4 catalyst
• this is how ethanol from ethene can be obtained

Question 19

why does an alcohol have a higher boiling point than a similar sized hydrocarbon?

Answer 19

• alcohol has hydrogen bonding between molecules, whereas hydrocarbon only has vdW forces between molecules
• hydrogen bonding is stronger than vdW (so more energy required to overcome these stronger hydrogen bonds)

Question 20

where is the ethene used to form ethanol through hydration obtained from?

Answer 20

crude oil (cracking of fractions from it)

Question 21

distillation apparatus diagram

Answer 21

Question 22

reflux apparatus diagram

Answer 22

Question 23

formation of ethanol from the hydration of ethene - conditions, advantages and disadvantages?

Answer 23

conditions:
• acid catalyst
• aqueous
• high temp
• high pressure
advantages:
• high percentage yield (ethanol is the only product)
disadvantages:
• ethene comes from crude oil - non renewable source
• more energy required than fermentation (so more expensive)

Question 24

how to test for an aldehyde/ketone?

Answer 24

• add Tollen’s reagent / Fehling’s solution
• if ketone present, then no reaction (remains clear -Tollens / blue - Fehling’s)
• if aldehyde present, then colour change to silver mirror (Tollen’s) / red precipitate formed (Fehling’s)

Question 25

what is a biofuel?

Answer 25

fuel obtained from living matter

Question 26

Why are anti-bumping granules added to a flask when refluxing?

Answer 26

to prevent large bubbles from forming

Question 27

In Europe, some of the glucose from crops is fermented to produce ethanol.

Use of a carbon-neutral fuel leads to no net emissions of carbon dioxide to the atmosphere.

The ethanol produced by fermentation of glucose may be regarded as a carbon-neutral fuel.

Justify this statement. Include the relevant chemical equations in your answer.

[4 marks]

Answer 27

• 6CO2 + 6H2O → C6H1206 + 602
• C6H12O6 → 2C2H5OH + 2C02
• 2C2H5OH + 6O2 → 4CO2 + 6H2O
• Hence, formation of glucose takes in 6CO2 and fermentation and combustion of ethanol gives out 6CO2

Question 28

Suggest why ethanol can be considered to be a carbon-neutral fuel.

Answer 28

• CO2 released by fermentation
• CO2 taken up in photosynthesis

Question 29

environmental impacts that come with using biofuels?

Answer 29

• deforestation / sacrificing land that could be used for food
• loss of biodiversity (due to loss of habitats)
• 6CO2 in and 6CO2 out, but it isn’t actually carbon neutral as fuel is used in production, distribution, etc.

Question 30

outline the reaction and conditions to form an aldehyde from the oxidation of an alcohol, and the further oxidation of the aldehyde to form a carboxylic acid

Answer 30

• 1° alcohol + [O] -> aldehyde + water
• aldehyde + [O] -> carboxylic acid + water
• warmed with acidified potassium dichromate (VI)
• distilled [aldehyde is distilled off - if this isn’t done, it would oxidise to form the carboxylic acid]

e.g. ethanol:

Question 31

Answer 31

Question 32

Answer 32