Question

Acetaldehyde and acetone can be distinguished by:
(a) Schiff's test
(b) Molisch's test
(c) Lucas test
(d) 2,4 DNP

Answer 1

Hint: We should know the observations of each detection test to distinguish between the two compounds. And we should also know the reagents involved and the reactions, the observations related to each functional group.

Complete step by step solution: In the question, two compounds are given and we have to distinguish between the two compounds. The principle of the detection test itself is that the components given for detection will have different functional groups or differences in the alkyl chain or differences in presence of multiple bonds etc.
So when a molecule is treated with reagents it will yield a product, i.e. a chemical change has occurred and the chemical change happened with a remarkable observation, like color change, the evolution of gas, precipitate formation, etc.
Let us discuss the differences and similarities in the compounds. So the given compound is acetaldehyde and acetone. Acetaldehyde is an aldehyde that has the formulae $C{{H}_{3}}CHO$, so a –CHO group is present in the compound.
Now let us talk about acetone, it is a ketone and it has the formulae, $C{{H}_{3}}COC{{H}_{3}}$.
So in both the compounds the common factor is the presence of the –CO group i.e the carbonyl functional group.
So the test that is used to distinguish between an aldehyde and a ketone will help us to distinguish between acetaldehyde and a ketone.
Let us discuss the given detection tests.
We know that Molisch's test is used for the detection of carbohydrates. If we add a compound which is a carbohydrate along with Molisch's reagent then it will form a purple ring.
Lucas test is the test used for the detection of alcohol. The Lucas tests distinguish between primary, secondary, and tertiary alcohols.
2,4 DNP test is used to find the presence of carbonyl group i.e if in the given mixture aldehyde or ketone is present or not.
Schiff's test is used to distinguish between ketone and aldehyde since the positive result will be shown for aldehydes only.
So from the above discussion, we could say that the test that can be used for distinguishing between ketones and aldehyde is Schiff's reagent.
Since only acetaldehyde will give the purple or magenta color when the analyte is added to Schiff's reagent.

So the correct answer for the above-given question is option (a).

Note: Schiff's reagent is a product that is formed during the reaction between the sodium bisulfite and fuchsin which has a dye formulation. The observation of this reagent is that Schiff's reagent produces a dark violet or magenta color. Schiff's reagent is also called a p-rosaniline hydrochloride solution.