what are all the compounds that gives positive test with fehling solution or tollens reagent or both?

prajwal, 9 years ago

Grade:12

2 Answers

Aarti Gupta

askIITians Faculty 300 Points

9 years ago

Tollen’s Reagent –
Tollens' reagent is usually ammoniacal silver nitrate.It is an chemical reagent most commonly used to determine whether a known carbonyl-containing compound is an aldehyde or alpha-hydroxy ketone.A positive test with Tollens' reagent results in elemental silver precipitating out of solution,on the inner surface of the test tube, producing a characteristic "silver mirror”.
1).Aldehydes will be positive in Tollens' test and a mirror-like material will be formed.
2).If the ketone is an alpha-hydroxy ketone, then the Tollens' reagent will react.
3).Tollens' reagent is also a test for alkynes with a triple bond in the 1-position. A yellow precipitate of the metal acetylide is formed in this case.

Fehling’s Solution –
Fehling's solution is a chemical test which is used to differentiate between water-soluble carbohydrate and ketone functional groups, and as a test for monosaccharides.It consist of Fehling's A and Fehling's B. Fehling's A is a blue aqueous solution of copper(II) sulfate, while Fehling's B is a clear and colorless solution of aqueous potassium sodium tartrate, known as Rochelle salt and a strong alkali which is commonly sodium hydroxide.
1).Aldehydes are oxidized with this solution giving a positive result, but ketones do not react, unless they are alpha-hydroxy-ketones.
2).Fehling's test is used as a test for monosaccharides. It will give a positive result for aldose monosaccharides (due to the oxidisable aldehyde group) but also for ketose monosaccharides, as they are converted to aldoses by the base in the reagent, and then give a positive result.For this reason, Fehling's reagent is sometimes referred to as a general test for monosaccharides.
Formic acid (i.e HCOOH - methanoic acid) is a compound which gives a positive test with Fehling's,as well as with Tollens' test. This is due to the fact because it is readily oxidizable to carbon dioxide and water.

Kushagra Madhukar

askIITians Faculty 628 Points

3 years ago

Dear student,

Please find the solution to your problem.

Tollen’s Reagent –

Tollens' reagent is usually ammoniacal silver nitrate.It is an chemical reagent most commonly used to determine whether a known carbonyl-containing compound is an aldehyde or alpha-hydroxy ketone.A positive test with Tollens' reagent results in elemental silver precipitating out of solution,on the inner surface of the test tube, producing a characteristic "silver mirror”.

1).Aldehydes will be positive in Tollens' test and a mirror-like material will be formed.

2).If the ketone is an alpha-hydroxy ketone, then the Tollens' reagent will react.

3).Tollens' reagent is also a test for alkynes with a triple bond in the 1-position. A yellow precipitate of the metal acetylide is formed in this case.

Fehling’s Solution –

Fehling's solution is a chemical test which is used to differentiate between water-soluble carbohydrate and ketone functional groups, and as a test for monosaccharides.It consist of Fehling's A and Fehling's B. Fehling's A is a blue aqueous solution of copper(II) sulfate, while Fehling's B is a clear and colorless solution of aqueous potassium sodium tartrate, known as Rochelle salt and a strong alkali which is commonly sodium hydroxide.

1).Aldehydes are oxidized with this solution giving a positive result, but ketones do not react, unless they are alpha-hydroxy-ketones.

2).Fehling's test is used as a test for monosaccharides. It will give a positive result for aldose monosaccharides (due to the oxidisable aldehyde group) but also for ketose monosaccharides, as they are converted to aldoses by the base in the reagent, and then give a positive result.For this reason, Fehling's reagent is sometimes referred to as a general test for monosaccharides.

Formic acid (i.e HCOOH - methanoic acid) is a compound which gives a positive test with Fehling's,as well as with Tollens' test. This is due to the fact because it is readily oxidizable to carbon dioxide and water.

Thanks and regards,
Kushagra