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GROUP NO 3
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* The Tollens test is used to determine whether
a particular compound is a ketone or analdehyde.* A positive result of the Tollens test would
indicate the presence of aldehydes .* This would result into the presence of a silver
precipitate, normally referred to as 'silvermirror'.
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* Tollens reagent is a chemical reagent mostcommonly used to determine whether a known
carbonyl-containing compound is an aldehyde ora ketone.
* It is usually ammoniacal silver nitrate, but canalso be other mixtures, as long as aqueous di-
amminesilver(I) complex is present.* It was named after its discoverer, the Germanchemist Bernhard Tollens .
http://en.wikipedia.org/wiki/Aqueous_solutionhttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Complex_(chemistry)http://en.wikipedia.org/wiki/Bernhard_Tollenshttp://en.wikipedia.org/wiki/Bernhard_Tollenshttp://en.wikipedia.org/wiki/Bernhard_Tollenshttp://en.wikipedia.org/wiki/Complex_(chemistry)http://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Aqueous_solution -
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* A positive test with Tollens' reagent results inelemental silver precipitating out of solution,
occasionally onto the inner surface of thereaction vessel.
* It produces a characteristic and memorable"silver mirror" on the inner vessel surface.
*
Aldehydes will be positive in Tollen's test and amirror-like material will be formed.
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* Procedure Place 1 ml of different sugars in 6test tubes.
* Glucose; Fructose; Sucrose; Galactose; Maltose;Lactose.
* Add 5 ml of ammoniacal solution of silvernitrate.
*
Heat in a boiling water bath for 5 minutes.* Observe what is formed in the sides of the test
tubes.
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* Normally, all of the sugars give positive test forTollens except for sucrose.
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All the other sugars are reducing sugars ,since they have a free aldehyde group to act astheir functional group.
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* Sucrose does not give positive for Tollens test.* Sucrose is a disaccharide made of glucose and
fructose linked via an ether bond between C1on the glucosyl subunit and C2 on the fructosylunit.
#C1 Carbon with aldehyde group#C2 Carbon with ketone group
* This bond is called a glycosidic linkage.* Therefore sucrose does not have a free
aldehyde or ketone functional group.
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Glycosidic Linkage
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* Since the fructose concentration was high inthe sucrose preparation, the sucrose samplealso showed positive for tollens test, in thisparticular experiment.
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![CH 17: Aldehydes and Ketones · 2019. 9. 11. · → O XIDATION TESTS FOR ALDEHYDES Tollen’s reagent = [Ag(NH3)2]OH Forms a silver mirror precipitate Reacts only with aldehydes,](https://static.cupdf.com/doc/110x72/60ac60877fd84432d010cf50/ch-17-aldehydes-and-ketones-2019-9-11-a-o-xidation-tests-for-aldehydes-tollenas.jpg)
