3.3.5 - ALCOHOLS Flashcards
State the functional group and general formula for alcohols
- “-OH”
- hydroxyl group
- CnH2nOH
State and describe the 3 ways of classifying an alcohol
PRIMARY ALCOHOLS
- -OH group is attached to a Carbon that is attached to 1 other Carbon
SECONDARY ALCOHOLS
- -OH group attached to a C that is attached to 2 other C’s
TERTIARY ALCOHOLS
- -OH group attached to a C that is attached to 3 other C’s
- what is the strongest intermolecular force that alcohols can form
- outline how this occurs
- hydrogen bonding
- O—H bond in hydroxyl group is polar, due to the electro negativity difference between the 2 atoms
- H bond can form between δ+ H atom and δ- O atom’s lone pair
State the 2 ways of producing alcohols (specifically ethanol)
- hydration of ethane
- fermentation of glucose
Outline the how ethanol can be produced by hydration of ethene
- include mechanism involved
- state the equation
- occurs via electrophilic addition
- C=C bond breaks
- H+ attaches
- H2O attaches to carbocation
- H2O loses a H to stabilise its positive charge
- C2H5OH produced + H+
- C2H4 + H20 ➡️ C2H4OH
State the conditions required for the hydration of ethene
- high temperature (300degrees C)
- high pressure 960-70atm)
- (phosphoric) acid catalyst, H+ ions required
State 3 advantages of using hydration of ethene to produce ethanol
- faster than fermentation
- produces pure ethanol, C2H5OH
- continuous process (products can constantly be removed if reactants are constantly being added)
State 3 disadvantages of using the hydration of ethene to produce ethanol
- high energy process
- requires an expensive plant to take place
- non-renewable fuels used as a reactant (C2H5 is a byproduct of fossil fuels)
Outline how fermentation of glucose can produce ethanol
- state the equation
- starch from crops broken down into glucose
- yeast (enzyme) anaerobically respires to break down glucose into ethanol and carbon dioxide
- C6H12O6 ➡️ 2 C2H5OH + 2 CO2
State the conditions requires for the fermentation of glucose
- why are these required?
30 - 37 DEGREES CELSIUS
- any higher would kill the yeast
- optimum temperature for yeast enzyme
ANAEROBIC CONDITIONS/NO OXYGEN
- yeast would areobically respire in the presence of O2
- this means they would produce CH3COOH instead of C2H5OH
State 3 advantages of using fermentation of glucose to produce ethanol
- low energy process
- uses renewable resources (plant material)
- simple equipment
State 3 disadvantages of using fermentation of glucose to produce ethanol
- slower than hydration of ethene
- batch process (loading reactants, separating products before the next batch), reducing efficiency
- produces CO2, a greenhouse gas
Define the term “biofuel”
Renewable fuels formed from living biological materials, e.g. plants
- which method of producing ethanol results in it being a biofuel
- why is this the case
- fermentation produces bio ethanol
- glucose that is fermented comes from starch, a material from plants
- why is it argued that ethanol fermentation is carbon-neutral
- use equations to explain
- PHOTOSYNTHESIS from plants (later used for glucose) during growth phase takes in 6 moles of CO2
6CO2 + 6H2O ➡️ C6H12O6 + 6O2 - FERMENTATION process occurs due to anaerobic respiration of yeast, producing 2 moles of CO2
C6H12O6 ➡️ 2C2H5OH + 2CO2 - COMBUSTION of ethanol when it is used releases 4 moles of CO2
2C2H5OH ➡️ 6H2O + 4CO2 - theoretically, shows that the Carbon given out during the process of making/using ethanol is equal to the Carbon taken in by plants during photosynthesis
- why is ethanol fermentation not truly carbon neutral
- state 3 examples that contradict the theory
- carbon given out during the process is not truly equal to carbon taken in by plants during photosynthesis
1. Fossil fuels are burned to produce fertilisers for crops
2. Energy is used by farm machinery
3. Transporting feedstock and ethanol itself uses energy - these add to CO2 emissions
- what substance is used to dehydrate alcohols
- state the word equation for the dehydration of alcohols
- what mechanism occurs
- excess, hot sulfuric acid, H2SO4
- alcohol + acid ➡️ alkene + water
- elimination
- which substance is used to oxidise alcohols
- how is this represented in equations
- acidified potassium dichromate
- H+/K2Cr2O7
- represented by (O) , oxidising agent
- how many times can primary alcohols be oxidised
- what are they oxidised into
- under which conditions
- oxidised 2 times
- alcohol ➡️ aldehyde under distillation
- aldehyde ➡️ carboxylate acid under reflux
What is the functional group for an aldehyde
C = O
\
H
What is the functional group for a ketone
O
||
R — C — R
State the colour change for primary alcohols when added to acidified potassium dichromate
Orange to green
- which type of alcohols turn acidified potassium dichromate orange to green
- which alcohols is potassium dichromate used to distinguish between
- primary and secondary
- distinguish between primary/secondary and tertiary
- tertiary stay orange
- how many times are secondary alcohols oxidised
- what are they oxidised into
- under what conditions
- oxidised once
- alcohol ➡️ ketone
- under reflux conditions
