Identifying Organic functional groups

Question 1

Alkene

Answer 1

C = C

• Add bromine water
• turns colourless from brown/orange

Question 2

Aldehyde

Answer 2

R - CHO

Tollen’s reagent:
- forms silver mirror

• 2-4, DNP - orange/yellow ppt THEN recrystallise ppt and compare melting point to known data to find carbonyl compound

Add acidified dichromate:
- Orange solution turns to green solution

Question 3

Ketone

Answer 3

R - CO - R

• 2-4, DNP - orange/yellow ppt THEN recrystallise ppt and compare melting point to known data to find carbonyl compound

Question 4

Carboxylic acid

Answer 4

COOH

• Add dilute solid or aqueous NA2CO3
• Effervescence

Question 5

Haloalkane

Answer 5

R - X

• Add ethanol (solvent)
  THEN
• Add aqueous acidified silver nitrate
• White ppt dissolves in DILUTE NH3
  (Chloroalkane)
• Cream ppt dissolves in CONC NH3 (Bromoalkane)
• Yellow ppt doesn’t dissolve in CONC NH3 (Iodoalkane)

Question 6

Alcohol (primary + secondary)

Answer 6

O-H

Add acidified dichromate:
- Orange solution turns to green solution