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?
Cn H2n+1 OH
How do you name alcohols?
Hydroxyl- or -OH
What kind of intermolecular forces do alcohols have? why?
Hydrogen boning, due to the electronegative difference in the OH bond
How do alcohols melting point and boiling points compare to other hydrocarbons of similar C chain lengths? 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 hydrogen bond in water Insoluble when long chain- non-polarity of C-H bond takes precedence
What make 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 (phosphoric acid catalyst H3PO4)
What are the advantages and disadvantages of making ethanol from crude oil?
Advantages- fast, continuous process, ethanol, has a high purity Disadvantages- not renewable as from crude oil
How can ethanol be made by fermentation?
Plant carbo hydrates broken down and fermented by enzymes in yeast —> ethanol
What conditions are needed for ethanol to be formed by fermentation?
Enzymes in yeast as catalyst, 35 degrees C, anaerobic conditions
Write an equation for the reaction which takes place when ethanol is being formed by fermentation
What are the advantages and disadvantages of making ethanol by fermentation?
Advantages- renewable as from plants Disadvantages- slow, batch process, enzymes stop working at 15% alcohol so the solution is not pure, needs to be fractionally 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, so it can’t be drunk)
Write an equation for the combustion of ethanol?
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 a 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