Testing for Aldehydes and Ketones Flashcards
1
Q
What chemically is tollen’s reagent?
A
- Contains silver ion complex Ag(NH3)2 +
- (silver nitrated + aqueous ammonia)
- Colourless solution
2
Q
How does tollen’s reagent work?
A
- Tests for Aldehydes
- Gently warmed with aldehyde
- Aldehyde is oxidised
- Ag(NH3)2 + ions reduced to solid metallic silver Ag
- Silver mirror is formed if aldehyde present
- Ketone, no reaction, cannot be oxidised by tollen’s reagent
3
Q
What is Fehling’s solution
A
- Alkaline solution containing Copper (II) ions
- Blue from Copper (II) ions
4
Q
How does Fehling’s solution work?
A
- Tests for aldehydes
- Aldehyde oxidised
- Becomes carboxylic acid
- Cu 2+ ions (blue) reduced to Cu + ions and copper oxide forms (brick red)
- If ketone reacts, nothing happens, not oxidised, so remains blue
5
Q
How can acidified potassium dichromate be used to distinguish between aldehydes and ketones?
A
- Aldehyde oxidised, orange to green
- Ketone not oxidised, no colour change