organic qualitative analysis

• Alkene

  • Test: Add bromine water
  • Observation: orange to colourless
• Haloalkane

  • Test: Add silver nitrate and ethanol and place in water bath @ 50C
  • Observation: chloroalkane forms white precipitate, bromoalkane forms cream precipitate, iodoalkane forms yellow precipitate
• Carbonyl

  • Test: Add 2,4-DNP
  • Observation: Orange precipitate
• Aldehyde

  • Test: Add Tollen's reagent and warm
  • Observation: Silver mirror
• Primary and secondary alcohols and aldehydes

  • Test: Add acidified potassium dichromate (VI) and warm in water bath
  • Observation: Colour change orange to green
• Carboxylic acid:

  • Test: Add aqueous sodium carbonate
  • Observation: Effervescence
• Phenol

  • Test: Add Br2
  • Observation: Bromine is decolourised and white precipitate is formed
• 2,4-DNP tests for carbonyl
• 2,4-DNP turns orange in the presence of a carbonyl
• Tollen's reagent tests for aldehyde and produces a silver mirror
• To test for phenol add Br2
• ALDEHYDES + KETONES GIVE AN ORANGE PRECIPITATE WITH 2,4 -DNP, TO FIND KETONE

  • FILTER TO GET IMPURE 2,4-DNP DERIVATIVE
  • RECRYSTALLISE THE IMPURE DERIVATIVE (orange precipitate)
  • MEASURE THE MELTING POINT OF THE PURIFIED DERIVATIVE
  • COMPARE TO DATA VALUES
• Tollen's reagent is a mild oxidising agent

  • it can oxidise aldehydes to carboxylic acid
  • it can't oxidise ketones