6 - Tests for organic functional groups Flashcards
1
Q
Alkene c=c
A
- Br2 water
- Br2 water decolourises orange to colourless
- a dibromoalkane is made
2
Q
Phenol C6H5OH
A
- pH indicator - weak acidity 5-6
- test with carbonates - no reaction (only carboxylic acids react
3
Q
Carbonyls (aldehydes or ketones)
A
- 2,4 DNPH (Brady’s)
- orange yellow hydrazine precipitate is made
- each hydrazine has a unique melting point
4
Q
Aldehyde -CHO
A
- Tollens reagent, warm in water bath
- silver mirror made
- Ag+ reduced to Ag
- aldehyde oxidised to carboxylic acid
5
Q
Carboxylic acid -COOH
A
- test with carbonates e.g. Na2CO3 solution
- Fizzing - CO2 produced
- Carbonates are weak acids but stronger than phenols
2H+ + CO32- ->CO2 + H2O
6
Q
Haloalkanes
A
AgNO3 in ethanol solvent, water, warm in water bath
- white precipitate of AgCl
- cream precipitate of AgBr
- yellow precipitate of AgI
Ag+(aq) + X-(aq) -> AgX(s)
7
Q
primary and secondary alcohols
A
- acidified dichromate H+/Cr2O72-
- potassium dichromate and H2SO4
- orange to green
- alcohol are oxidised
- tertiary alcohols cannot be oxidised
Cr2O72- -> Cr3+
