Testing for Organic Functional Groups

Question 1

Testing for Alkenes

Answer 1

• Orange bromine water added
• Sample shaken
• If alkene, colourless solution forms
• Electrophilic addition

Question 2

Testing for Alcohols

Answer 2

• Add acidified potassium dichromate (K2Cr2O7, acidified with H2SO4)
• Heat
• Primary or secondary alcohols present, orange to green
• Tertiary alcohols present, no change

Question 3

Testing for Aldehydes

Answer 3

Tollens Reagent
- Warm
- Silver Nitrate + Excess Ammonia
- Ag+ reduced to Ag atoms
- Silver mirror forms
.
Fehling’s solution
- Clear blue to opaque red
- Copper (II) Sulphate solution
- Cu2+
- Reduced to Cu+

Question 4

Testing for Carboxylic Acids

Answer 4

• Add Na2CO3
• CO2 gas emitted
• Test gas with limewater
• Turns cloudy
• Or use pH probe, universal indicator, litmus paper