Tests for functional groups

Question 1

Test for alkene

Answer 1

1. Add bromine water

colour change from orange to colourless

Question 2

Test for haloalkane

Answer 2

1. Add aqueous AgNO3 solution and ethanol and heat to 50 Celsius

Chloroalkane - white precipitate
Bromoalkane - cream precipitate
Iodoalkane - Yellow precipitate

Question 3

Test for C=O carbonyl

Answer 3

1. Add 2,4-dinitrophenylhydrazine (2,4-DNP)

Orange/yellow precipitate

Question 4

Test for aldehyde

Answer 4

1. Add Tollen’s reagent and warm

A silver mirror is formed

                                        OR 1. Add Fehling's solution

The blue solution produces a dark red precipitate

Question 5

Test for primary/secondary alcohol and aldehyde

Answer 5

1. Add acidified potassium dichromate and reflux

colour change from orange to green

Question 6

Carboxylic acid

Answer 6

1. Add aqueous Na2CO3 solution

effervescence is observed