6

• What two reactants are used to synthesize methyl 3-nitrobenzoate?

  Methyl benzoate and nitric acid
• What is the purpose of concentrated sulfuric acid in the synthesis of methyl 3-nitrobenzoate?

  It acts as a catalyst to speed up the reaction
• What temperature should be kept below during the preparation of methyl 3-nitrobenzoate?

  Below 10°C
• Why should the temperature be kept below 10°C during the preparation of methyl 3-nitrobenzoate?

  To maximize the yield of the product
• Describe the process of filtration under reduced pressure.

  • Place filter paper in a Büchner funnel
  • Position funnel in a Büchner flask and connect to a water pump
  • Turn on tap to create vacuum and pour solution into funnel
  • Rinse solid on filter paper with solvent after draining
• Describe the process of recrystallisation.

  • Dissolve solid in minimum volume of hot solvent
  • Filter to remove insoluble impurities
  • Cool the filtrate
  • Filter to remove soluble impurities, leaving product on filter paper
• Why is ethanol used for the recrystallisation of methyl 3-nitrobenzoate?

  Ethanol dissolves methyl 3-nitrobenzoate but not water
• Why is the product dissolved in a minimum amount of solvent during recrystallisation?

  To prevent product loss when cooled
• How does recrystallisation improve the purity of a product?

  It separates impurities that are insoluble
• Why is the solution cooled in ice immediately after recrystallisation?

  To decrease solubility and promote crystallisation
• Why must the crystals be completely dry before measuring their mass?

  Excess solvent could falsely increase yield
• How can percentage yield be calculated?

  (Actual yield ÷ theoretical yield) x 100
• Give three reasons why the yield may be lower than 100%.

  • Product loss during filtering or transferring
  • Some product remains in solution after recrystallisation
  • Side reactions may occur
• What technique could be used to investigate the purity of the product before and after recrystallisation?

  Thin layer chromatography comparing Rf values
• What apparatus is used to transfer a small amount of liquid onto the chromatography plate?

  Capillary tube
• Why should the beaker containing the solvent and the TLC plate be covered with a clear watch glass?

  To prevent evaporation of the solvent
• In chromatography, what is the solvent front?

  The furthest distance travelled by the solvent
• Why should the baseline be drawn in pencil on a TLC plate?

  Pencil is insoluble and won't obscure results
• What is used to make the spots visible in chromatography for methyl 3-nitrobenzoate?

  Iodine crystals
• How do you calculate an Rf value?

  Rf = distance substance / distance solvent
• Without using chromatography, how can the purity of a sample be assessed?

  • Use melting point apparatus
  • Pure substances have a specific melting point
  • Impure substances melt over a larger range
• What safety precautions should be taken during this practical?

  • Wear safety goggles to avoid irritants
  • Avoid contact with iodine crystals
  • Keep ethanol away from naked flames