6 - TESTS FOR ALCOHOL, ALDEHYDES, ALKENES, CARBOXYLIC ACIDS

• IDENTIFICATION OF ALCOHOLS?

  • for primary and secondary alcohols
  • acidified potassium dichromate
  • turns orange to green
  • primary alcohols oxidised to aldehydes then carboxylic acids
  • secondary alcohols oxidised to ketones
  • Cr (VI) (orange) is reduced to Cr (III) (green)
• IDETIFICATION OF ALDEHYDES?

  1. Tollen's reagent

  • silver mirror produced
  • aldehyde oxidised to carboxylic acid
  • [Ag(NH3)2]+ reduced to Ag and 2NH3

  1. Fehling's solution

  • red precipitate formed
  • aldehyde oxidised to carboxylic acid
  • Cu (2+) reduced to Cu+
  • both are weakly oxidising which is why they are only able to oxidise aldehydes not alcohols
• IDENTIFICATION OF ALKENES?

  • shake with bromine water
  • orange solution turns colourless
  • electrophilic addition
• IDENTIFICATION OF CARBOXYLIC ACIDS?

  • add sodium carbonate
  • effervescence
  • 2RCOOH + Na2CO3 -> 2RCOONa + CO2 + H2O