Tests for functional groups

alkene

add bromine water drop-wise

orange = colourless

haloalkane

add AgNO₃ + ethanol

warm to 50° in a waterbath

chloroalkane = white precipitate

bromoalkane = cream precipitate

iodoalkane = yellow precipitate

carbonyl

add 2,4-DNP

orange precipitate

aldehyde

add Tollens’ reagent

warm

silver mirror

primary/secondary alcohol and aldehyde

add K₂Cr₂O₇/H₂SO₄

warm in water bath

orange = green

carboxylic acid

add Na₂CO₃(aq)

effervescence

phenol

bromine

white precipitate

OR pH indicator paper (acidic)

carbonate ion

1) add HNO₃

2) bubbles = carbonate

3) to confirm, bubble the gas through limewater = limewater turns cloudy

sulfate ion

1) add Ba(NO₃)₂

2) white precipitate forms = sulfate ion present (BaSO₄ formed)

ammonium ion

1) add NaOH (aq)

2) warm the mixture

3) hover moist pH indicator paper above solution = turns blue = ammonia gas produced