Alcohols Flashcards
What is the general formula of an alcohol?
CₙH₂ₙ₊₁OH
Volatility of alcohols:
low
Boiling points of alcohols:
high
Why do alcohols have high boiling points?
high boiling points due to their ability to form
hydrogen bond between alcohol molecules
What are the different types of alcohols?
[3]:
- Primary alcohols
- Secondary alcohols
- Tertiary alcohols
What makes a secondary alcohol?
Secondary alcohols are alcohols where 2 carbon are attached to the carbon with the functional group
What happens when you oxidise a primary alcohol?
An aldehyde is formed
Partial oxidation of primary alcohols:
primary alcohol → aldehyde
What are the reagents in the partial oxidation of primary alcohols?
[2]:
- potassium dichromate (VI) solution
- dilute sulfuric acid
What are the conditions in the partial oxidation of primary alcohols? [3]:
- Limited amount of potassium dichromate (VI)
- Warm gently
- Distil out the aldehyde
What does the dichromate ion look like?
Cᵣ₂O₇²⁻
What would you observe when dichromate ions are reduced? [2]:
- Orange → Green
- Cᵣ₂O₇²⁻ reduced to Cr³⁺
What do you do when writing the formula of aldehydes in a condensed way?
write CHO and not COH
e.g.CH₃CH₂CHO
Distillation equipment [5]:
- Thermometer
- Bung
- Heat
- Leibig condenser
- Collection flask
- Anti bumping granules
Where should the thermometer be during distillation and why?
- At the T junction connecting to the condenser
- To measure the correct boiling point
Why are electric heaters often used to heat organic chemicals?
Organic chemicals are normally highly flammable and could set on fire with a naked flame
Full Oxidation of Primary Alcohols:
primary alcohol → carboxylic acid
What are the reagents for the full oxidation of primary alcohols? [2]:
- potassium dichromate(VI) solution
- dilute sulfuric acid
What are the conditions for the full oxidation of primary alcohols? [3]:
- an excess of dichromate
- heat
- under reflux
What is reflux used for? [2]:
- Reflux is used when heating organic reaction mixtures for long periods
- The condenser prevents organic vapours from escaping
by condensing them back to liquids
Why do you never seal the end of the condenser during reflux?
build up of gas pressure could cause the apparatus to explode
Why are anti bumping granules added to the flask during distillation and reflux?
To prevent vigorous, uneven boiling by making small bubbles form instead of large bubbles
Reflux equipment [4]:
- Anti-bumping granules
- Round-bottomed flask
- Heat
- Condenser
Oxidation of secondary alcohols:
secondary alcohol → ketone
What are the reagents for the oxidation of secondary alcohols? [2]:
- potassium dichromate(VI) solution
- dilute sulfuric acid
What are the conditions for the oxidation of secondary alcohols?
heat under reflux
Observation for the oxidation of secondary alcohols?
the orange dichromate ion Cᵣ₂O₇²⁻ reduces to the green Cr³⁺+ ion
Why can tertiary alcohols not be oxidised by potassium dichromate?
There is no hydrogen
atom bonded to the carbon with the -OH group
What is the difference between aldehydes and ketones?
Aldehydes can be further oxidised to carboxylic acids whereas ketones cannot be further oxidised
What tests are used to distinguish between aldehydes and ketones? [2]:
- Tollens’ Reagent
- Fehling’s solution
How is Tollens’ reagent formed?
[2]:
- By mixing aqueous ammonia and silver nitrate.
- Forms the ion [Ag(NH₃)₂]⁺
What are the conditions for Tollens’ reagent?
Heat gently
Tollens’ reagent observation
[2]:
- Aldehydes = silver mirror
- Ketones = no visible change
What does Fehling’s solution contain?
Blue Cu²⁺ ions
What are the conditions for Fehling’s solution?
Heat gently
Fehling’s solution observations
[2]:
- Aldehydes = Blue Cu 2+ ions in
solution change to a red precipitate of Cu₂O - Ketones = no visible reaction
How else can a carboxylic acid be tested for?
[2]:
- Tested by addition of sodium carbonate
- It will fizz and produce carbon dioxide
Reaction of Alcohols with Dehydrating Agents:
Alcohol → Alkene
Reagents for the reaction of alcohols with dehydrating agents? [2]:
Concentrated sulfuric or phosphoric acids
What are the conditions for the reaction of alcohols with dehydrating agents?
Warm under reflux
What is the mechanism for the reaction of alcohols with dehydrating agents?
elimination
What does producing alkenes from alcohol provide?
provides a possible route to polymers without using monomers derived from oil
What are the methods for the formation of ethanol?
[2]:
- Fermentation
- Industrial formation from ethene
What are the conditions for fermentation? [3]:
- Yeast
- No air/ anaerobic
- Temperatures 30-40ᵒC
What is the optimum temperature for fermentation and why? [3]:
- Around 38ᵒC
- At lower temperatures the reaction is too slow.
- At higher temperatures the yeast dies and the enzymes
denature
Why is fermentation done in the absence of air?
[2]:
- The presence of air can cause extra reactions to occur.
- It oxidises the ethanol produced to ethanoic acid
(vinegar)
Advantages of fermentation [2]:
- Sugar is a renewable resource
- Production uses low-level technology / cheap
equipment
Disadvantages of fermentation [3]:
- Batch process is slow and gives high production
costs - Ethanol made is not pure and needs purifying by
fractional distillation - Depletes land used for growing food crops
What type of reaction is the industrial formation of ethanol from ethene?
Hydration/ addition
Conditions for the industrial formation of ethanol from ethene
[3]:
- high temperature 300 °C
- high pressure 70 atm
- strong acidic catalyst of conc H₃PO₄
What are the advantages of the industrial formation of ethanol from ethene?
[3]:
- faster reaction
- purer product
- continuous process (which means cheaper manpower)
What are the disadvantages of the industrial formation of ethanol from ethene?
[3]:
- high technology equipment needed (expensive
initial costs) - ethene is non-renewable resource (will become
more expensive when raw materials run out) - high energy costs for pumping to produce high
pressures
What is ethanol?
A biofuel produced from plants
What is the ethanol produced from fermentation?
A biofuel
What does carbon neutral mean?
an activity that has no net annual carbon (greenhouse gas) emissions to the atmosphere
