26.2 identifying aldehydes and ketones Flashcards
1
Q
what is 2,4-dinitrophenylhydrazine also called?
A
Brady’s reagent
2
Q
what is 2,4- DNP used to detect?
A
presence of a carbonyl group
3
Q
what coloured precipitate forms in the presence of a carbonyl group?
A
orange
4
Q
describe the procedure for the detection of a carbonyl group
A
- add 5cm of 2,4-DNP
- add 3 drops of unknown compound
- if no crystals form, add a few drops of sulphuric acid
- orange precipitate forms if positive
5
Q
what is Tollen’s reagent used to detect?
A
presence of an aldehyde group
6
Q
describe the procedure for making Tollen’s reagent
A
- add 3cm of AgNO3(aq)
- add NaOH(aq) until a brown precipitate is formed
- add dilute NH3 until a clear colourless solution is formed
7
Q
describe the procedure for testing for aldehydes
A
- add 2cm to unknown solution to test tube
- add an equal volume of Tollen’s reagent
- leave in a warm water bath for 10-15 minutes
- if silver mirror forms, positive result
8
Q
what happens to the aldehyde in Tollen’s reagent test
A
aldehyde is reduced to carboxylic acid as Ag+ is reduced to Ag
9
Q
what symbol is used to show a oxidising agent?
A
[O]