PMT flashcards - organic synthesis

• Why is the minimum volume of hot solvent used in recrystallisation?

  To create a saturated solution for crystal formation
• Why is the solution filtered hot during recrystallisation?

  To remove insoluble impurities and prevent crystal formation
• Why is the solution cooled in an ice bath during recrystallisation?

  To maximize crystal formation and increase yield
• Why are the crystals washed with cold water during recrystallisation?

  To remove soluble impurities from the crystals
• How would you separate the crystals from the reaction mixture in recrystallisation?

  Filter under reduced pressure using a Buchner funnel
• Why might the percentage yield be below 100% in practical scenarios?

  Product loss during filtration, drying, and weighing
• What are the reasons for percentage yield being below 100%?

  • Product lost during filtration
  • Product lost during drying and weighing
  • Some product remains dissolved in solution
  • Crystals left on filter paper
  • Sample may still be wet
• How is Quickfit apparatus connected?

  Grease joints with petroleum jelly before connecting
• Why is continuous water flow necessary around the condenser in distillation?

  To keep the water cool for effective distillation
• Describe a method to separate immiscible liquids.

  1. Pour mixture into a separating funnel
  2. Add distilled water and stopper
  3. Invert to mix and equalize pressure
  4. Shake until no 'whistle' sound
  5. Open stopper to collect lower layer
  6. Use another beaker for the organic layer
  7. Shake with drying agent
• Name two drying agents used in organic chemistry.

  Magnesium sulphate and Calcium chloride
• How is a drying agent used in organic chemistry?

  Add to organic product until clumps move freely
• What does re-distillation mean?

  • Purification of a liquid
  • Achieved through multiple distillations
• What are the three key steps to purify an organic solid?

  1. Filtration under reduced pressure
  2. Recrystallisation
  3. Measurement of melting points