The Tollens Reagent


The Tollens reagent is a chemical reagent used to distinguish between ketones and aldehydes. It uses silver nitrate in a solution containing sodium hydroxide and ammonia. Acetaldehyde is an example of an aldehyde.

Tollens’ reagent

Tollens’ reagent is a chemical test used to determine aldehydes and ketones. It is a mixture of silver nitrate, ammonia, and sodium hydroxide. When used correctly, this reagent is highly reliable and sensitive to determining a substance’s chemical composition.

Ketones are oxidizable by Tollens’ reagent, while aldehydes are not. The former has attached hydrogen and cannot be oxidized, while the latter lacks it. Ketones are also tested using Tollens’ reagent, which also works for alkynes that contain a triple bond in the carbonyl position. It also gives a positive test when used with Fehling’s reagent.

To make the Tollens’ reagent, you must mix equal amounts of silver nitrate and sodium hydroxide. The silver nitrate solution should darken in a minute. It should then form a silver mirror.

Fehling’s Detail Explanation

Fehling’s reagent is a solution that can be used to determine the presence of reducing sugar or aldehyde in substances. It is also helpful for screening for diabetes. The solution breaks down starch and maltodextrins into glucose syrup and DE, revealing their levels. The solution is also helpful for testing for formic acid in a urine sample.

The reagent contains diamine silver(I) ions. This ion is easily reduced by acid or base and leaves a silvery mirror. In contrast, Ketones hurt the test and do not produce a silver mirror.

A positive result is obtained if the unknown solution reacts with Tollens’ reagent. The unknown solution is added to three mL of 95% ethanol and allowed to stand for 15 minutes. If the reaction is negative, the unknown solution is not aldehyde-free. It may contain aldehyde or ketone impurities.

Benedict’s Detail Explanation

Benedict’s test is a simple chemical reaction used to determine the presence of reducing sugars in analytes. The reagent used in this test is composed of sodium citrate, sodium carbonate, and copper II sulphate pentahydrate. It reacts with the reducing sugars to form a brick-red precipitate. To perform the test, mix the analyte samples with the reagent and then heat the mixture in boiling water for three to five minutes. The resulting residue confirms the presence of reducing sugars in the analyte.

The Tollens reagent has several advantages over Fehling’s reagent. It can be selective for aldehydes and ketones while leaving alcohol unaffected. To prepare the reagent, add 50 ml of AgNO3 to 25 ml of KOH, and stir the solution thoroughly. After five minutes, the precipitate will dissolve in the aqueous ammonia.

Tollens reagents can be used to distinguish between aldehydes and ketones. The silver nitrate in the solution will oxidize an aldehyde into a carboxylic acid. Moreover, the silver ion in the silver solution will be reduced to a solid silver Ag(s). The test tube’s walls will become a silver mirror when this occurs. By contrast, ketones will not react with the Tollens reagent.


The Tollens reagent is a chemical reagent used to identify aldehydes and ketones. It is composed of a solution of silver nitrate and ammonia, with sodium hydroxide added to maintain a basic pH. The solution forms a silver mirror on the inner surface of the reaction vessel.

The reagent oxidizes aldehydes and ketones by reducing them to their carboxylic acid form. The silver ion is then reduced to metallic silver, or Ag(s), in the case of acetaldehyde. The resulting carboxylate ion gives carboxylic acid when the solution is acidified. However, producing carboxylic acid directly in the Tollens reagent is impossible under an alkaline environment. Further, acetaldehyde does not react with Ketones do not get oxidized by Tollens reagent.

The Tollens reagent can be prepared for several applications, but it should be prepared immediately before using it. Otherwise, it can form a potentially explosive substance. It can be prepared by combining a finger-deep solution of silver nitrate with an equal amount of ammonia.