3.3.5 Alcohols Flashcards
What is the functional group of the alcohol homologous series?
OH
Hydroxyl group
What is the difference between primary, secondary and tertiary alcohols?
Primary- one alkyl group attached to the carbon that is attached to the OH
Secondary- two alkyl group attached to the carbon that is attached to the OH
Tertiary- three alkyl group attached to the carbon that is attached to the OH
What is the trend in boiling points of alcohols?
The boiling point increases as the size of alcohols increases.
The size of the van-der-waals forces between molecules increases
What is the difference between boiling points of alcohols and alkanes and why?
The boiling points of alcohols is higher than alkanes of similar molecular mass.
The presence of oxygen results in alcohols being polar molecules.
There is also hydrogen bonding which is stronger than van der waals forces.
Why are alcohols soluble in water?
They hydrogen bond due to presence of oxygen.
Why are larger alcohols less soluble?
There becomes greater proportion of the molecule which isn’t polar.
Why is hydrogen bonding weaker in tertiary alcohols?
Steric hindrance means other alkyl groups get in the way of hydrogen bonding.
The OH in primary alcohol allows other molecules to come closer to increases the strength of hydro-green bonding.
Why is hydrogen bonding weaker in tertiary alcohols?
Steric hindrance means other alkyl groups get in the way of hydrogen bonding.
The OH in primary alcohol allows other molecules to come closer to increases the strength of hydro-green bonding.
What is the bond angle of alcohols and why?
105*
The oxygen in the OH group has 2 bonding pairs and 2 lone pairs
Lone pairs repel more strongly.
What is dehydration of alcohols used for?
To produce alkenes from alcohols
Advantages of dehydration of alcohols compared to producing alkenes using crude oil
It is sustainable if the alcohols was made via fermentation of glucose from plants
Normally alkenes are made from crude oil which is non-renewable so this is more sustainable when making polymers and plastics
What is dehydration?
Elimination of a water molecule
What are the catalysts for dehydration of alcohols?
Aluminium oxide OR sulphuric/phosphoric acid catalyst
What mechanism illustrates the dehydration of alcohols?
Elimination
Why does dehydration of secondary or tertiary alcohols produce multiple products?
Because the C=C double bond can form either side of the C that had the OH group
Why is distillation needed after dehydration of alcohols?
As we get impure product so used to separate the useful alkene
How does distillation separate different alkenes?
By boiling point
What is hydration of alkenes used for?
To produce alcohols
What are the conditions for hydration of alkenes?
High pressure of 60 atm
High temperature of 300*c
Steam
Acid catalyst (concentrated phosphoric)
What are the advantages of producing alcohols via direct hydration?
Continuous process that makes pure ethanol
Fast rate of reaction
What is fermentation?
An alternative way to produce alcohols using glucose from plants
What are the conditions for fermentation and why?
Anaerobic conditions (no oxygen)
Yeast (enzyme to convert glucose to ethanol and CO2)
Temperature of 30-40*c - optimum temperature for yeast to operate / not denature
How is pure ethanol obtained after fermentation?
Fractional distillation
Give reasons why/why not fermentation is carbon neutral?
-number of moles of carbon used is the same as the number of moles of carbon produced when burnt so no net carbon change
-however fuels are burnt to transport biofuels and machinery to harvest crops so increased carbon emissions.
