Alcohols
- Created by: Emily Cartwright
- Created on: 07-04-14 09:13
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- Alcohols
- 'An alcohol is a compound which contains the functionla group -OH, which is called an alcohol group'
- Naming Alcohols
- Simple alcohols are names by finding the right name for the carbon skeleton and adding -ol at the end to signify the alcohol
- A number may also be used in the name to signify the position of the alcohol group e.g. propan-2-ol
- Physical Properties
- Solubility in Water
- Alcohols with short carbon chains e.g. ethanol are very soluble in water. This is because the -OH group is able to form hydrogen bonds to water
- Alcohols with longer carbon chains are less soluble in water because the carbon part is non-polar and cannot form hydrogen bonds in water
- Relatively low volatility
- Alcohols are harder to vaporise than hydrocarbons with molecules of a similar size
- This is because alcohols can also form hydrogen bonds which are much stronger than van der Waals forces and take more energy to break
- Alcohols are harder to vaporise than hydrocarbons with molecules of a similar size
- Solubility in Water
- Preperation of Alcohols
- Hydration of Alkenes
- Alkenes will react with steam in the presence of a phosphoric acid catalyst to form alcohols
- This is an electrophilic addition reaction and because water is added it is referred to as hydration
- Alkenes will react with steam in the presence of a phosphoric acid catalyst to form alcohols
- Hydration of Alkenes
- Uses and production of ethanol
- Uses include;
- As a solvent, most commonly in an impure form called methylated spirit
- In the form of alcoholic drinks
- As a biofuel
- Hydration of Ethene
- The most important method of making industrial ethanol in the UK, as petrol can easily be obtained by cracking of petroleum
- Conditions; Ethene and steam are passed over a phosphoric acid catalyst
- Advantages
- Ethene can be easily obtained by cracking of petroleum- so it is convenient in countries with a petrochemical industry
- It can be operated as a continuous process, so it can be fuel and time efficient
- Pure ethanol is easily obtained rather than a dilute solution
- Disadvantages
- The petroleum needed is non-renewable
- If the ethanol produced is used as fuel it will add new CO2 to the atmosphere, contributing to climate change
- Fermentation from sugars e.g. Glucose
- Plant material containing sugars or starch can be fermented into ethanol. This is how drinks are made but it is also increasingly being used to produce industrail ethanol
- Reaction: C6H12O6 -> 2C2H5OH + 2CO2
- The necessary conditions are;
- Temperature of about 30-35 degrees
- Absence of air
- Water
- Yeast
- The fermentation process can continue until the solution contains about 15% ethanol but no more otherwise ethanol of this concentration kills the yeast
- Disadvantages
- The reaction has to be stopped when the concentration of ethanol becomes too high which is less efficient
- It produced a dilute aqueous solution, from which the ethanol has to be distilled
- Advantages
- Ethanol produced this way is potentially a carbon neutral fuel because the CO2 released when burned was taken in from the atmosphere when the plant was growing
- The sugars needed as the feedstock are a renewable resource because we can grow new plants
- Uses include;
- Uses of Methanol
- As an additive to petrol. It improved combustion, allowing the hydrocarbons to burn more smoothly
- As a feedstock for the production of other industrially important chemicals which may be used in the production of plastics
- Reactions of Alcohols
- Combustion
- Ethanol and other alcohols burn readily in air, forming carbon dioxide and water
- Dehydration
- Also know as elimination of water
- An elimination reaction is one in which atoms are lost from the starting molecule without being replaced by new ones
- Heat alcohol with a concentrated acid - usually sulphuric acid or phosphoric acid
- Esterification
- 'An alcohol reacts with a a carboxylic acid in the presence of a concentrated sulphuric acid catalyst to form an ester'
- Carboxylic acids are compounds which contain the group -COOH
- When carboxylic acids react with alcohols, the hydrogen of the -OH group of the carboxylic acid is replaced by the alkyl group from the alcohol
- Carboxylic Acid + Alcohol -> Ester + Water
- Conditions: The carboxylic acid and the alcohol are heated together with a concentrated sulphuric acid catalyst
- Properties and Uses;
- Low molecular weight esters are volatils, with a fruity smell occur in fruits and other natural products and esters are used in artificial fruit flavourings and in perfumes
- Some esters are also important as solvents
- Combustion
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