3.3.5 Alcohols Flashcards
What substance causes alcohol to oxidise?
Potassium dichromate K2Cr2O7 is an oxidising agent that causes alcohols to oxidise
What are the products of the following reactions:
-partial oxidation of a primary alcohol
-full oxidation of a primary alcohol
-full oxidation of a secondary alcohol
-aldehyde + water
-carboxylic acid + water
-ketone + water
What is the key difference in properties of aldehydes and ketones?
aldehydes can be further oxidised to carboxylic acids
ketoens cannot be further oxidised
chemical basis for tests
Describe the Tollens’ reagent
Formed:
Conditions:
Reaction:
Observation:
Equation for Aldehyde
Reagent:
Tollens’ reagent formed by mixing aqueous ammonia and silver nitrate.
The active substance is the complex ion of [Ag(NH3 )2 ]+ .
Conditions: heat gently
Reaction:
aldehydes only are oxidised by Tollens’ reagent into a carboxylic acid.
The silver(I) ions are reduced to silver atoms
Observation:
with aldehydes, a silver mirror forms coating the inside of the test tube.
Ketones result in no visible change
CH3CHO + 2Ag+ + H2O -> CH3COOH + 2Ag + 2H+
Describe the test using Fehling’s solution
Reagent:
Conditions:
Reaction:
Observation:
Equation for Aldehyde:
ON GOOGLE DOC
How do we test for the presence of a carboxylic acid?
add sodium carbonate
fizz and produce carbon dioxide
Describe the reaction of alcohols with dehydrating agents
Reaction:
Reagents:
Conditions:
Role of Reagent:
Type of Reaction:
ON GOOGLE DOC
Draw the mechanism for the acid-catalysed dehydration, using ethanol as an example
ON GOOGLE DOC
What are the ways of forming ethanol?
fermentation
hydration of ethene
Describe the formation of ethanol from ethene
Reagents:
Type of Reaction:
Conditions:
Reagent: Ethene (from cracking of fractions from distilled crude oil)
Reaction: Hydration
Conditions:
ON GOOGLE DOC
Draw a mechanism for the hydration of ethene
ON GOOGLE DOC
Write the equation for the fermentation of glucose to produce ethanol:
ON GOOGLE DOC
What are the conditions for fermentation?
yeast
no air
temperatures 30-40 degrees celcius
Why is fermentation done in the absence of air?
to prevent further extra reactions occuring
can oxidise ethanol to produce ethanoic acid
Why is the optimum temperature for fermentation around 38 degrees?
lower temperatures = too slow
enzyme that convert sugars in ethanol/carobn dioxide is most effective in this range
higher temperatures the yeast die and enzymes denature
What is a biofuel?
Fuel produced from plants
What does carbon neutral mean?
An activity that has no net annual carbon emissions to the atmosphere
Why is the production of bioethanol not carbon neutral, despite the equations saying so?
There is energy used and hence carbon dioxide released from burning of fossil fuels used to
power machinery
the engines of transportation systems
energy used for fractional distillation (fermentation)
Give the equations to show that fermentation of glucose produces no net contribution to CO2
ON GOOGLE DOC
Give disadvantages of the use of crops for the production of ethanol: MS [5]
Growth is subject to the environment
Reduces land available for food growth
Requires the use of fossil fuels
Not carbon neutral
Requires significant processing after production to separate the ethanol from water
Explain why bromine, a non-polar molecule, is able to react with propene: MS [4]
Double bonds are electron rich and can act as electron pair donors
The bromine becomes polarised and forms an induced dipole
Bromine is an electrophile - a lone pair acceptor
The addition reaction converts the double bond to a single bond
State the advantages of the fermentation of glucose method for making ethanol [3]
Low-tech
Cheap equipment
Renewable resources only
State the disadvantages of the fermentation of glucose for making ethanol [3]
Fractional distillation step required for purification
Batch process takes time and money
Depletes land used for growing food crops
State the advantages of the hydration of ethene method for making ethanol
Faster reaction
Purer product
Continuous process (cheaper manpower)
State the disadvantages of hydration of ethene method for making ethanol [3]
High technology equipment needed
Ethene is non-renewable
High energy costs for pumping to produce high pressures
General Formula for Alcohols
ON GOOGLE DOC
How can we classify alcohols?
ON GOOGLE DOC
What are the bond angles in alcohols?
ON GOOGLE DOC
Why do alcohols have relatively low volatility and high boiling points?
ON GOOGLE DOC
Describe the partial oxidation of Primary Alcohols
ON GOOGLE DOC
Draw the equation for the partial oxidation of propanol
ON GOOGLE DOC
What observation is made during partial oxidation of primary alcohols?
ON GOOGLE DOC
How do we write out the formula of an aldehyde?
CHO (NOT COH)
Draw a distillation apparatus
ON GOOGLE DOC
Describe the full oxidation of primary alcohols
reaction?
reagent?
conditions?
ON GOOGLE DOC
What is distillation?
A separation technique used to separate an organic product from its’ reacting mixture
Why are electric heaters used to heat organic chemicals?
organic chemicals are normally highly flammable
could set a fire with a naked flame
What is reflux?
Apparatus that involves the continuous evaporation and condensation of organic reaction mixtures for long periods.
Why do we never seal the end of the condenser in a reflex?
ON GOOGLE DOC
What is the purpose of anti bumping granules in reflux / distillation?
ON GOOGLE DOC
Describe the oxidation of secondary alcohols
ON GOOGLE DOC
Why can tertiary alcohols not be oxidised by potassium dichromate?
There is no hydrogen atom bonded to the carbon with the -OH group
Draw the oxidation of propan-2-ol
ON GOOGLE DOC
