Tests for functional groups

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Tests No.1:

Test for alkene:

  • Add bromine water and shake OR
  • Add bromine in hexane and shake

Observation:

  • The colour changes from orange to colourless
  • The colour changes from brown to colourless.

Test for alcohol group:

  • Add dry PCl5

Observation:

  • Steamy white fumes which turn damp blue litmus paper red
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Tests No. 2:

Test for halogenoalkane:

  • Add aqueous NaOH and heat.
  • Add excess dilute nitric acid and silver nitrate solution.
  • Add dilute or concentrated aqueous ammonia.

Observation:

With C-Cl (chloroalkane): A white precipitate forms which is soluble in dilute aqueous ammonia.

With C-Br (bromoalkane): A cream precipitate forms which is only slightly soluble in dilute aqueous ammonia/ soluble in concentrated aqueous ammonia.

With C-I (iodoalkane): A yellow precipitate forms which is insoluble in dilute aqueous ammonia/insoluble in concentrated aqueous ammonia.

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Tests No. 3:

Test for primary/secondary/tertiary alcohols:

  • Add potassium dichromate (VI) solution and dilute sulphuric acid and heat
  • K2Cr2O7 solution + dilute H2SO4 + heat
  • Add potassium manganate (VII) solution and dilute sulphuric acid and heat
  • KMnO4 + dilute H2SO4 + heat

Observations:

With primary alcohol: Orange to Green

With secondary alcohol: Orange to Green

With tertiary alcohol: Orange remains Orange

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Tests No. 4:

Tests for aldehydes and ketone:

  •  Add-2,4-DNP (dinitrophenylhydrazine)

Observation with aldehydes and ketone:

  • An orange precipitate is formed.

Tests for carboxylic acids:

  • Add aqueous Na2CO3 or aqueous NaHCO3

Observation with carboxylic acids

  • Effervescence is observed.
  • A colourless gas forms which turns limewater cloudy.
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Tests No. 5:

Tests for methyl secondary alcohols and methyl ketones:

  • Add iodine and aqueous NaOH to the compound and heat.

Observation with methyl secondary alcohols and methyl ketones:

  • A pale yellow precipitate of CHI3 is formed.

Test for aldehydes:

  • Add Tollen's reagent (ammonical silver nitrate solution) and heat OR
  • Add Fehling's solution and heat

Observations with aldehydes:

With Tollen's reagent: A silver mirror is formed with the aldehyde

With Fehling's solution: The blue solution turns to a red precipitate with the aldehyde.

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