Alcohols

HideShow resource information
View mindmap
  • 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
    • 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
    • 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 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

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all Functional Groups resources »