RP5: Distillation

• Condenser:

  • Open at both ends
  • Cold water flows around the outside
  • Water enters the bottom and leaves the from the top
• Condenser - Cools the hot vapour and condenses it back to a liquid
• Anti-bumping granules prevent the formation of large bubbles or bumping of equipment
• Primary alcohol -> COOH:

  • Reflux used as it doesn't allow any reactant vapour to escape
• Reflux:

  • Aldehyde vapour rises and enters condenser
  • Aldehyde cools and condenses then drops back into a reaction mixture
  • Open top to prevent pressure build up
• Reaction mixture should contain primary alcohol, h2so4, potassium dichromate and anti-bumping granules
• Distillation apparatus needs thermometer to allow collection of the product only by checking the suitable temperature range
• Ice bath placed under receiving flask to prevent evaporation of product (distillate)
• Why distillation is used to produce and aldehyde:

  • Allows aldehyde to escape the reaction mixture and prevents further oxidation
• For a high yield of aldehyde:

  • Use distillation
  • Heat at the boiling point of aldehyde
  • Collect aldehyde as it is distilled off
• Precaution with preparations:

  • Wear gloves as acid can be corrosive
  • Use fume cupboard as volatile organic solvents are toxic
  • Keep away from naked flame as organic solvents are flammable
  • Periodically release pressure inside flask so prevents build-up
• Anhydrous solids may be used because they do not react with the reactants
• Adding lots of distilled water may remove any water soluble impuritites
• Describe reflux and why it is needed to make acids:

  • Heat to boiling point for a prolonged period of time
  • Aldehyde and alcohol will evaporate and cool back down into reaction mixture
  • When aldehyde and alcohol condense back down into the reaction mixture it can then be oxidised
• How to obtain an ethanal sample from a mixture:

  • Mixture heated in a suitable flask
  • With a still head containing a thermometer
  • Water-cooled condenser connected to still hand
  • With a beaker in an ice bath
  • Cooled collection vessel necessary to reduce evaporation of ethanal
• Reflux is used to prevent the escape of the reaction vapour