9A - testing for functional groups

homologous series

a family of organic compounds with the same functional groups which differ by a CH₂ group with each successive member

what properties do different functional groups affect?

physical properties

tests used to determine presence of C=C double bonds

1. Bromine water - Br₂(aq)

2. potassium permanganate - KMnO₄(aq)

positive reaction to Bromine water test

brown → colourless

why is brown → colourless a positive reaction for C=C double bonds?

• reflects that an addition reaction has ocurred

• as the C=C double bonds are broken, the brown Br₂(aq) is consumed and leaves a colourless solution.

positive reaction to potassium permanganate test for C=C double bonds (acidified conditions)

purple → colourless

positive reaction to potassium permanganate test for C=C double bonds (alkaline conditions)

purple → dark green (intermediate) → brown/black (precipitate)

tests for hydroxyl groups

1. acidified potassium dichromate

2. lucas test

3. tollens’ test

4. sodium metal test

5. esterification

what does the acidified potassium dichromate determine

the presence of either primary or secondary alcohols

positive acidified potassium dichromate test

• The dichromate ions will go from orange → green

• indication the the substance is either a primary or secondary alcohol which has oxidised

What does the Lucas test determine?

the presence of alcohols

positive acidified lucas test

colourless → cloudy

What does the tollens’ test determine?

presence of aldehyde