15 - Alcohols Flashcards
What is the general formula of an alcohol?
CnH2nOH
What is the functional group of an alcohol?
A hydroxyl group, -OH
What naming does an alcohol give?
Either -ol or, if other functional groups are present, hydroxy-
What bond angles does an alcohol have, and where?
109.5 between C and H
104.5 between C-O-H (2 electron pairs force it down by 5 degrees)
What are the classes of alcohols?
Primary, secondary and tertiary. This is determined by the number of alkyl groups the C that contains the -OH group is attached to.
How does the boiling point of alcohols change with chain length?
As chain length increase, so does boiling point. This causes a greater number of points of contact, therefore increasing van der Waal forces, hence a higher energy is required.
How do side chains affect boiling point of alcohols?
An increased number of side chains pushes the molecules apart. This reduces the van der Waals, and hence the boiling point.
Why do alcohols have higher boiling points than alkanes?
The -OH group can form hydrogen bonds, which are stronger than the van der Waal forces.
Explain the solubility of alcohols.
Short chain alcohols are soluble in water, as the -OH group forms hydrogen bonds with the water.
However in long chain alcohols, the -OH group is unable to overcome the hydrophobic essential of the carbon chain, hence they are insoluble. This occurs at pentanol.
What are the two methods of ethanol production?
The hydration of ethene from crude oil
Fermentation of yeast
What conditions does hydration of ethene occur under?
300C
60 atm
Phosphoric acid catalyst
When does fermentation stop?
When the solution becomes 15% ethanol concentration.
What conditions does fermentation occur under?
35C
Anaerobic
What is meant by carbon-neutral?
There is no net release of carbon. The carbon released is equal to that taken in.
Why would some people not describe the fermentation process as carbon neutral?
There are carbon costs related to transport.
The product also needs to be fractionally distilled, which requires additional energy.
What type of process is fermentation of ethanol?
Batch
What does the elimination reaction of an alcohol form?
An alkene and water
How does dehydration occur? (2 methods)
Alcohol is heated under reflux with excess hot concentrated phosphoric acid
Alcohol vapours are passed over heated aluminium oxide.
How is dehydration a renewable method of making plastics?
Ethanol can be derived from fermentation, and then can be used in dehydration.
What is a biofuel?
A fuel produced from a biological resource.
State one condition necessary to ensure the complete combustion of a fuel in air.
Excess oxygen
Give two conditions for elimination of a halogenoalkane to an alkene.
Hot
Ethanol as solvent
Concentrated hydroxide
Identify a catalyst for the electrophilic addition of ethene.
Concentrated phosphoric acid.
Give the IUPAC name for a 5 carbon chain and ketone on the second carbon.
Pentan-2-one
Approximately how pure is ethanol produced by fermentation?
15%
What are primary alcohols oxidised to?
Aldehydes/carboxylic acids
How can a ketone be formed?
Oxidation of secondary alcohols
What oxidising agent is used to oxidise alcohols?
Acidified potassium dichromate (VI)
How can an oxidising agent be represented in a reaction?
[O]
How can ethene be renewable?
Fermentation forms ethanol
Ethanol can be dehydrated to ethene
Give the equation for the complete combustion of ethanol.
C2H5OH + 3O2 goes to 2CO2 + 3H2O.
How to use apparatus to collect a sample of ethanol? (6)
Turn on water
Heat with Bunsen Burner
Produces water/ethanol vapours
Vapours pass up fractionating column, where ethanol and water are seperated.
Water condenses back into flask
Observe thermometer temperature to keep temperature below boiling point of ethanol
Only ethanol vapour passes into condenser
Why open tap of separating tunnel periodically?
Release pressure
Why is sodium carbonate used to wash distillate?
Removes acid
Give two properties of a good drying agent?
Absorb water
Do not react with product
