3.5 Alcohols
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What is the functional group of an alcohol?
Hydroxyl group -OH
What is the general formula of an alcohol?
CnH2n+1OH
How do you name alcohols
Hydroxyl or OH
What kind of intermolecular forces do alcohols have? Why?
Hydrogen bonding, due to the electronegativity difference in the OH bond
How do alcohols m.p and b.p compare to other hydrocarbons of similar C chain length? Why?
Higher because they have hydrogen bonding—> stronger than van der waals forces
Are alcohols soluble in water? Why does solubility depend on chain length?
Soluble when short chain - OH hydrogen bonds to hydrogen bond in water Insoluble when long chain-non polarity of C-H bond takes precedence
What makes an alcohol primary?
C bonded to OH is only bonded to one other C atom
What makes an alcohol secondary?
C bonded to OH is bonded to two other C atoms
What makes an alcohol tertiary?
C bonded to OH is bonded to three other C atoms
How can ethanol be made from crude oil?
Hydration of ethene via electrophilic addition
What are the advantages and disadvantages of this method?
Advantages- fast, continuous process, ethanol has a high purity Disadvantage- not renewable as from crude oil
How can ethanol be made by fermentation?
Plant carbohydrates broken down and fermented by enzymes in yeast—> ethanol
What conditions are needed for this reaction to take place?
Enzymes is yeast as catalyst 35 degree Celsius anaerobic conditions
Write an equation for the reaction which take place
C6H12O6(aq) —> 2C2H5OH + 2CO2
What are the advantages and disadvantages of this method?
Advantages - renewable as from plants Disadvantages- slow, batch process, enzymes stop working at 15% alcohol so solution is not pure needed to be fractional distilled
In the future how might most ethene be made? Why is it not made like this at the moment
Dehydrate ethanol made by fermentation —> ethene Not economical at the moment
Define carbon neutral
No net addition of CO2 to the atmosphere Carbon dioxide released when combusted = carbon dioxide absorbed as a plant
Explain how using ethanol in petrol engines could be considered to be carbon neutral
Carbon dioxide released in fermentation and combustion = carbon dioxide absorbed when growing
Why would it probably not be entirely carbon neutral to use ethanol
Other “carbon costs” associated with it e.g. transport
What is a commercial fuel that uses ethanol? What else does it contain and why?
Methylated spirits- methanol (toxic-can’t be drunk)
Write an equation for the combustion of ethanol
C2H5OH (l) + 3O2 (g) —> 2CO2(g) + 3H2O(l)
What is an elimination reaction
The removal of a smaller molecule from a larger one
Which group leaves the parent molecule in the case of alcohols?
OH and H (to form water)
What physical conditions are needed for the elimination reaction from alcohols to alkenes? (2 alternatives)
Excess hot concentrated sulphuric acid or pass vapour over hot aluminium oxide