practicals

• What is the principle of recrystallisation?

  • Dissolve organic solid and impurities in hot solvent
  • Cool solution to crystallise solid
  • Minimum solvent used to avoid product loss

  
• What is the purpose of hot filtration in recrystallisation?

  To remove insoluble impurities

  
• How can product crystals be recovered after cooling?

  By filtration
• What apparatus speeds up the filtration process in recrystallisation?

  Buchner apparatus
• What is the significance of melting point in determining purity?

  It indicates purity and identity of a solid
• What effect do impurities have on the melting point?

  They lower the melting point
• What characterizes pure substances in terms of melting point?

  They have sharp, well-defined melting points
• How does the melting point range indicate purity?

  A broad range indicates impurities present
• What are the key skills needed for a melting point test?

  Preparing tubes, slow heating, repeating measurements
• What is the melting point of pure aspirin?

  135 °C
• Why is benzoic acid suitable for recrystallisation?

  It dissolves in hot water, not cold
• What is the minimum amount of hot water needed to dissolve 1.0 g of impure benzoic acid?

  30−35 cm³
• What is the purpose of a pre-heated glass funnel in hot filtration?

  To prevent premature solidification
• What can help initiate crystallisation if it is difficult to achieve?

  Agitating the flask or scratching walls
• What is the melting point of 3-nitromethyl benzoate?

  78 °C
• What safety precautions should be taken when handling concentrated acids?

  Wear safety glasses and gloves
• What are the key steps in the preparation of ethyl ethanoate?

  1. Mix ethanol, glacial ethanoic acid, and sulfuric acid
  2. Heat under reflux for 15 minutes
  3. Pour into sodium carbonate solution
  4. Use separating funnel to isolate ester
  5. Add sodium sulfate to dry the product
• What is the purpose of anti-bumping granules in the reaction mixture?

  To prevent vigorous boiling
• How is the product separated after the reaction mixture is neutralized?

  Using a separating funnel

  
• What happens to the boiling point of the ester compared to its reactants?

  It has a lower boiling point
• What is the process of purification by distillation?

  • Heat the mixture to vaporize the component
  • Collect the vapor and condense it back to liquid
  • Separate based on boiling points
• What is the first step in separating the ester?

  Separate the ester into an oily layer
• What is done after transferring contents to a separating funnel?

  A stopper is added to the funnel
• How many times should the separating funnel be inverted?

  15−20 times
• What happens to the ethyl ethanoate during separation?

  It floats on top of the aqueous solution
• What is done after the two layers are allowed to separate?

  The aqueous layer is drained away
• What is added to dry the ethyl ethanoate?

  A little solid sodium sulfate
• What is the purpose of a separating funnel in this procedure?

  • Cleans and isolates the product
  • Separates different liquid layers

  
• How is ethyl ethanoate purified?

  By distillation
• Why does the ester have a lower boiling point?

  It lost hydrogen bonds from reactants
• What is noted during the distillation of ethyl ethanoate?

  The temperature at which it distills
• What are the key hazards associated with concentrated sulfuric acid?

  It is very corrosive
• Why should safety glasses and gloves be worn?

  To protect against corrosive substances
• What should be done with ethyl ethanoate due to its properties?

  Handle it in a fume cupboard
• How can the identity of an ester be established?

  By its boiling point
• What is done to purify the resulting carboxylic acid?

  It is recrystallised
• Why must the acid hydrolysis of an ester be heated under reflux?

  To speed up the slow reaction
• What is a suitable ester for hydrolysis and identification?

  Methyl benzoate
• What is the hydrolysis reaction of methyl benzoate?

  $C_6H_5COOCH_3 +$$H_2O \rightarrow C_6H_5COOH +$$CH_3OH$
• What happens when the warm mixture is poured into cold water?

  Benzoic acid precipitates out