Tests for functional groups

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

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.

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

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.

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.