Question

Write a chemical test to distinguish between aldehyde and ketone (Give reason).

Answer 1

Hint: Ketones and aldehydes are organic compounds that contain a group of carbonyls. A carbonyl group is a compact group consisting of a double bonded carbon atom with an oxygen atom i.e., $C=O$. These carbonic chemical compounds can be artificially produced.

Complete step-by-step answer:
Its chemical structure is the major difference between aldehydes and ketones. Such measures that allow them to differentiate between themselves are the Schiff 's test, Tollen's test, Fehling 's test, Sodium hydroxide test etc.
Here we will consider 2 types of test for differentiating between ketone and aldehydes and they are:
Fehling's Test
Fehling 's check is a solution usually prepared fresh in laboratories. The solution initially appears in the form of two different solutions known as Fehling's A and Fehling's B. Fehling's A is a blue-coloured solution containing copper sulphate $CuS{O}_4$. Fehling's B is a transparent liquid consisting of potassium sodium tartrate also called Rochelle salt and a strong alkali, normally sodium hydroxide $NaOH$.
Solution A and B are prepared separately and processed during the test solutions
The two solutions are subsequently combined in equivalent quantities to produce the final colour-deep blue Fehling solution. The deep blue component is $C{u}^{2+}$ Complex bis(tartrate). The tartrate tetra-anions in solution act as a chelating agent
The result is positive if reddish brown precipitate is produced while the result is negative if there is no sign of such a shift
Reactions during this process are: -
$RCHO+2C{u}^{2+}+5O{H}^{-}\to RCO{O}^{-}+C{u}_{2}O+3H_{2}O$
Aldehydes continue to become oxidized, giving good outcomes. Ketones do not react apart from the alpha-hydroxy-ketones
The Silver Mirror Test also known as Tollens’s Test
Tollens Reagent refers to the chemical reagent used in the identification of a functional aldehyde group, an aromatic aldehyde functional group, or a functional alpha hydroxy ketone group in a given test material.
The Tollens Reagent is named after the German chemist Bernhard Tollens, who invented this reagent and its uses. Tollens reagent is a Silver Nitrate $AgN{O}_3$and Ammonia $N{H}_3$ solution.
An aqueous solution of silver nitrate is added with a few drops of dilute NaOH. The aqueous Silver Nitrate solution contains complexes of silver aquo where water serves as a ligand. Such silver aquo complexes are now converted into silver oxides by the hydroxide ions. This silver oxide ($A{g}_{2}O$) from this solution precipitates like a brown solid. We can write the reaction as : -
$2AgN{O}_3+2NaOH\to A{g}_{2}O+2NaN{O}_3+H_{2}O$
The brown silver oxide precipitate produced in phase 1 now dissolves with aqueous ammonia. The solution that emerged from this addition of aqueous ammonia contains the complex $[Ag(N{H}_3{)}_2{]}^{+}$. That complex is Tollens Reagent's primary component. The reaction can be given as
$A{g}_{2}O+4N{H}_3+H_{2}O\to 2[Ag(N{H}_3{)}_2]N{O}_3+2NaOH$
This test makes use of the reagent of Tollen’s that contains the $[Ag(N{H}_3{)}_2{]}^{+}$ complex. It is easily produced by combining watery ammonia with wet silver nitrate.
When aldehyde is heated with the reagent Tollens solid silver metal as $A{g}^{+}$ is reduced to $Ag$. And forms a film of metallic silver whereas in ketone there is no reaction.
In both the tests we can observe that ketones do not react and we can easily deduce the difference between aldehyde and ketone.

Note: The solution to Fehling is mainly corrosive in nature and we must always wear safety equipment including goggles and gloves whereas in Tollens test it is generally referred to as the Silver Mirror test because this film of metallic silver is produced on the test tube. We must always remember this while performing either of the tests.