Wednesday, March 21, 2012

Tollen’s Test for Aldehydes

Cyclohexanone and Benzaldehyde

Add one drop or a few crystals of unknown to 1 mL of the freshly prepared Tollens reagent. Gentle heating can be employed if no reaction is immediately observed.
Tollens reagent: Into a test tube which has been cleaned with 3M sodium hydroxide, place 2 mL of 0.2 M silver nitrate solution, and add a drop of 3M sodium hydroxide. Add 2.8% ammonia solution, drop by drop, with constant shaking, until almost all of the precipitate of silver oxide dissolves. Don't use more than 3 mL of ammonia. Then dilute the entire solution to a final volume of 10 mL with water.

Positive Test
Formation of silver mirror or a black precipitate is a positive test.


The test tube must be clean and oil-free if a silver mirror is to be observed.
Easily oxidized compounds give a positive test. For example: aromatic amine and some phenols.
Cleaning up
Place all solutions used in this experiment in an appropriate waste container.


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