After learning about different functional groups, let's learn how to identify them in A-Level Chemistry!
Testing for Alkanes and Alkenes
Add bromine water - decolourises alkene solution (with or without UV light). However, it can decolourise an alkane solution in the presence of UV light only.
Testing for Haloalkanes
Haloalkanes undergo nucleophilic subsitution, hence when warming with sodium hydroide, they form alcohols and the halogen ion. This halogen ion can then be tested with the silver nitrate:
- Add a few drops of dilute nitric acid. This prevents the formation of other insoluble silver compounds. You cannot use HCL because it contains chloride ions.
- Add silver nitrate solution and look for precipitate.
- Add ammonia solution for further testing.
Testing for Carboxylic acids
Just add a metal carbonate - it will produce effervescence.
Testing for Aldehydes and Ketones
The carbonyl group can be tested by adding 2,4 DNP which turns from yellow solution to orange yellow precipitate of which the melting point is specific to the actual ketone or aldehyde.
To distinguish between the two:
Testing for Amines and Amino acids
Add aqueous Cu2+ ions - it will form a dark blue ammonia complex.
Drafted by Eunice (Chemistry)
References:
- https://socratic.org/questions/557d014a581e2a2c3ac57f2d
- https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Book%3A_Organic_Chemistry_Lab_Techniques_(Nichols)/06%3A_Miscellaneous_Techniques/6.04%3A_Chemical_Tests/6.4D%3A_Individual_Tests
- https://in.pinterest.com/pin/587227238909965525/
- https://www.youtube.com/watch?v=O9U5Z4BlXhk