Tests for Organic Compounds

A1 and A2

test for alkenes

decolourises bromine water

test for halogenoalkanes

silver nitrate solution, test precipitate with NH3

Cl- white ppt soluble in dilute NH3

Br- cream ppt soluble in conc NH3

I- yellow ppt insoluble in NH3

test for alcohols

oxidise with acidified potassium dichromate (H+/Cr2O7^2-)

orange to green (primary and secondary)

no colour change for tertiary

OR

oxidise with acidified potassium manganate (VII) (H⁺/MnO₄^-)

purple to colourless (1^o and 2^o)

no colour change for 3^o

test for aldehydes and ketones

react with 2,4-DNPH

yellow-orange ppt

OR

oxidise with acidified potassium permanganate (H⁺/MnO₄^-)

→ can oxidise ketones because strong ox. agent

test(s) for aldehydes ONLY

Tollen’s reagent + heat → silver mirror produced (Ag+ → Ag)

Fehling’s reagent + heat → blue sltn to brick red ppt (Cu²⁺ → Cu)

react with acidified potassium dichromate (VI) → orange to green sltn

→ won’t ox. ketones because not strong enough ox. agent

test for carboxylic acids

test pH with probe → less than 7

react with carbonate → effervescence as CO2 formed

methyl ketone or 2^o alcohol

iodoform reaction:

halogenation: add I² and NaOH (aq) with heat (forms a -C(I)₃ group)

hydrolysis: NaOH (aq) forms a sodium carboxylate salt and IODOFORM (CHI₃₎, a yellow ppt