alcohols [O1] PAPER 2 Flashcards
what is the functional group of an alcohol?
-OH
outline the reaction, conditions and reagent used to form a carboxylic acid from the oxidation of an alcohol
• 1° alcohol + 2[O] -> carboxylic acid + water
• conditions: under reflux
• reagent: acidified potassium dichromate (VI)
e.g.
outline the reaction and conditions for the formation of a ketone from an alcohol
• 2° alcohol + [O] -> ketone + water
• acidified potassium dichromate (VI)
• reflux
e.g.
can a tertiary alcohol undergo oxidation?
no
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
• 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
fermentation conditions and equation?
• 35°C
• anaerobic
• (enzymes from) yeast / zymase
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.
• advantage – ethanol is produced at a faster rate
• disadvantage – more energy is used / required in the reaction
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?
Air gets in / oxidation occurs
State the meaning of the term carbon-neutral
no net / overall carbon dioxide emissions to the atmosphere
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.
(a) • (enzymes from) yeast / zymase
• 35°C
• anaerobic / no oxygen / no air
(b) fractional distillation
state the meaning of the term “hydration”
addition of water
Give one advantage and one disadvantage of manufacturing ethanol by fermentation rather than by hydration.
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
Reagent, conditions and mechanism for the dehydration of an alcohol to form an alkene?
• conc. sulfuric/phosphoric acid
• hot
• elimination
a mixture of alkenes can be formed depending on the alcohol (different carbocations)
Give one advantage of using ethanol as a fuel compared with using a petroleum fraction.
sugar/glucose/ethanol is renewable
Give a suitable reagent and reaction conditions for the oxidation of ethanol to form the carboxylic acid as the major product
• reagent - potassium dichromate (VI)
• conditions - acidified/sulfuric acid
what can alkenes formed through the dehydration of alcohols be used for?
form addition polymers without having to use monomers derived from crude oil
what is the role of potassium dichromate (VI) in the oxidation of alcohols?
• oxidising agent
• it is reduced as the alcohol oxidises (so goes from orange to green)
name the reaction, conditions and outline the mechanism to form an alcohol from an alkene
• electrophilic addition (hydration too)
• alkene + steam -> alcohol
• conc. H2SO4 catalyst
• this is how ethanol from ethene can be obtained
why does an alcohol have a higher boiling point than a similar sized hydrocarbon?
• 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)
where is the ethene used to form ethanol through hydration obtained from?
crude oil (cracking of fractions from it)
distillation apparatus diagram
reflux apparatus diagram
formation of ethanol from the hydration of ethene - conditions, advantages and disadvantages?
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)
how to test for an aldehyde/ketone?
• 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)
what is a biofuel?
fuel obtained from living matter
Why are anti-bumping granules added to a flask when refluxing?
to prevent large bubbles from forming
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]
• 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
Suggest why ethanol can be considered to be a carbon-neutral fuel.
• CO2 released by fermentation
• CO2 taken up in photosynthesis
environmental impacts that come with using biofuels?
• 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.
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
• 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:
