Reactions of alkenes and alcohols

• Structure and formulae of alkenes:

  • Alkenes have the general formula CnH2n
  • They have at least one carbon-carbon double bond, making them unsaturated because they contain two fewer hydrogen atoms than the alkane with the same number of carbon atoms
  • The first 4 alkenes are ethene, propene, butene, and pentene
• Reactions of alkenes:

  • Alkenes have the functional group C=C
  • They react with oxygen in combustion reactions, burning in air with smoky flames due to incomplete combustion
  • Alkenes react with hydrogen, water, and halogens by adding atoms across the carbon-carbon double bond to form a single bond
  • In each reaction with hydrogen, water, and halogens, the C=C bond is broken to form a C-C bond
  • The compound added splits into two groups added to the different carbons in the C=C bond
• Alcohols:

  • Alcohols contain the functional group -OH
  • The first 4 members of the series are methanol, ethanol, propanol, and butanol
• Reactions of methanol, ethanol, propanol, and butanol:

  • Alcohols burn in air, producing carbon dioxide and water
  • They dissolve in water to form a neutral solution with a pH of 7
  • Alcohols react with sodium to produce hydrogen and a salt
  • Alcohols react with oxidising agents to form carboxylic acids
• Uses of methanol, ethanol, propanol, and butanol:

  • Methanol is used as a chemical feedstock, in anti-freeze, and to make biodiesel
  • Ethanol is the main alcohol in alcoholic drinks, used as a solvent and fuel
  • All 4 alcohols can be used as fuels
• Producing ethanol:

  • Ethanol can be produced by fermentation of sugar with yeast using renewable sources
  • Conditions for fermentation: about 35°C, anaerobic, and yeast enzyme catalyst
  • Sugar → ethanol + carbon dioxide
• Carboxylic acids:

  • Ethanoic acid is a member of the carboxylic acids, having the functional group -COOH
  • The first four members are methanoic acid, ethanoic acid, propanoic acid, and butanoic acid
• Reactions of methanoic acid, ethanoic acid, propanoic acid, and butanoic acid:

  • They dissolve in water to produce acidic solutions with a pH less than 7
  • They react with metal carbonates to produce carbon dioxide, a salt, and water
  • React with alcohols in the presence of an acid catalyst to produce esters
  • Carboxylic acids do not ionise completely in solutions, making them weak acids with a higher pH than solutions of strong acids of the same concentration