reactions of alkenes and alcohols

• what are alkenes?

  • alkenes are hydrocarbons with a double carbon-carbon bond. the general formula for the homologous series is CnH2n
  • alkene molecules are unsaturated because they contain two fewer hydrogen atoms than the alkane with the same number of carbon atoms
  • ethene, propene, butene and pentene
• reactions of alkanes?

  • alkenes have the functional group c=c
  • alkenes react with oxygen in combustion reactions in the same way as other hydrocarbons, but tend to turn in air with smoky flames because of incomplete combustion
  • alkenes react with hydrogen, water and halogens by addition of atoms across the carbon double bond so that it becomes a single bond.
• addition reactions?

  • an addition reaction is one whereon molecule combines with another molecule forming one larger molecule and no other products.
  • alkanes cannot take part in addition reactions
• alcohols

  • contain functional group -OH
  • methanol, ethanol, propanol, butanol
  • alcohols can be represented as CH3CH2OH
• uses of alcohols?

  • aqueous solutions of ethanol are produced when sugar solutions are fermented using yeast
  • used as a fuel for vehicles
  • can be produced using fermentation and concentrated with fractional distillation
• fermentation

  • yeast provides the enzyme needed for fermentation
  • if cells become too cold, fermentation happens very slowly
  • if yeast cells become too hot, their enzymes become denatured and fermentation stops
  • conditions = sugars dissolved in water
  • air lock to allow carbon dioxide out and stop air from getting in
  • warm temperature, 25-35*C
• reactions of alcohols

  • combustion = ethanol + oxygen -> carbon dioxide + water
  • sodium = bubbles of hydrogen gas are produced. sodium + ethanol -> sodium ethoxide + hydrogen
  • water = solubility of alcohols decrease as the length of the alcohol molecule gets longer, butanol is less soluble than propanol
  • oxidation = ethanol +oxidising agent -> ethanoic acid + water. alcohols are oxidised without combustion to produce carboxylic acids.
• carboxylic acids

  • functional group -COOH
  • methanoic acid, ethanoic acid, propanoic acid, butanoic acid
• reactions of carboxylic acids with alcohol

  • carboxylic acids react with alcohols to make esters, which are organic compounds which contain all the functional group COO.
  • esters have fruity smells and can be used as solvents
  • ethyl ethanoate
  • alcohol + carboxylic acid -> ester + water
• properties of carboxylic acids

  • dissolve in water to form acidic solutions with pH values less than 7
  • react with metals to form a salt and hydrogen
  • reacts with bases to form a salt and water
  • reacts with carbonates to form a salt and carbonate
• carboxylic acids - weak acids

  • carboxylic acid solutions have a smaller amount of hydrogen ions
  • they partially ionise in water
  • the pH of a weak acid will be higher than the pH of a strong acid if their concentrations are the same