Give Simple Chemical Tests to Distinguish Between (NEET Chemistry)

 

a.)   Propanal and Propanone

b.) Acetophenone and Benzophenone

c.) Phenol and Benzoic acid

d.) Benzoic acid and Ethyl benzoate

e.) Pentan-2-one and Pentan-3-one

f.) Benzaldehyde and Acetophenone

g.) Ethanal and Propanal

Hint:  The key to differentiating these compounds lies in their functional groups. Tests like Tollen’s test and Fehling’s test are commonly used to distinguish between aldehydes and ketones.

Complete step by step answer:

(i) Propanal and Propanone

Tollen’s test is used to differentiate aldehydes from ketones.

Aldehydes yield a positive result, producing a silver mirror, while ketones do not react in this test.

Thus, Propanal shows a positive result, whereas Propanone shows a negative result.

(ii) Acetophenone and Benzophenone

The iodoform test is specific for methyl ketones, which show a positive result.

Acetophenone is classified as a methyl ketone, whereas benzophenone is categorized as a phenyl ketone.

 Hence, acetophenone produces a positive iodoform test, forming a yellow precipitate of iodoform in an alkaline iodine solution, whereas benzophenone does not react and shows a negative result.

(iii) Phenol and Benzoic Acid

Ferric chloride test – phenols show a violet color in this test.

Phenol interacts with neutral ferric chloride, forming an iron-phenol complex that produces a violet color.

In contrast, benzoic acid reacts with neutral ferric chloride to form a buff-colored precipitate of ferric benzoate.

(iv) Benzoic Acid and Ethyl Benzoate

Sodium bicarbonate test – this test yields a positive result for acids.

Benzoic acid, as an acid, produces a positive reaction with sodium bicarbonate, releasing carbon dioxide gas as effervescence.

In contrast, ethyl benzoate does not react with sodium bicarbonate and thus gives a negative result in this test.

(v) Pentan-2-one and Pentan-3-one

Iodoform test – this test is positive for methyl ketones.

Since Pentan-2-one is a methyl ketone, it gives a positive result, producing a yellow precipitate of iodoform when reacted with an alkaline iodine solution.

On the other hand, Pentan-3-one is an ethyl ketone, so it yields a negative result in the iodoform test.

(vi) Benzaldehyde and Acetophenone

Tollen’s test – aldehydes produce a positive result with this test.

Benzaldehyde, being an aldehyde, reduces Tollen’s reagent, forming a reddish-brown precipitate.

Acetophenone, on the other hand, is a ketone and thus gives a negative result in Tollen’s test.

(vii) Ethanal and Propanal

Iodoform test – this test yields a positive result for methyl ketones.

Ethanal contains a methyl group attached to the carbonyl carbon, so it gives a positive result in this test.

Propanal, however, does not react and thus shows a negative result in the iodoform test.

Note: Fehling’s Test is also used to differentiate aldehydes from ketones. Aldehydes show a positive result, while ketones do not. For instance, Propanal, as an aldehyde, reduces Fehling’s solution, producing a red-brown precipitate of cuprous oxide.

\( \text{CH}_3\text{CH}_2\text{CHO} + 2\text{Cu}^{2+} + 5\text{OH}^- \rightarrow \text{CH}_3\text{CH}_2\text{COO}^- + \text{Cu}_2\text{O}\downarrow + 3\text{H}_2\text{O}
\)