Name: Acetaldehyde and Acetone
Uploaded: 2019-07-19
Duration: 3 min 15 s
Description: Do you know carbonyl compounds are used in medicines? In this video, you will be able to understand the important uses of the two most common compounds, acet...

Question

How aldehydes and ketones are distinguished? Give two chemical reactions.

Accepted Answer

Aldehydes and ketones can be distinguished by the following tests.

(i)Tollen's test:

Aldehydes reduce Tollen's reagent. But, ketones do not reduce Tollen's reagent.

Example: Propanal is an aldehyde. Thus, it reduces Tollen's reagent. But, propanone being a ketone does not reduce Tollen's reagent.

$\underset{Propanal}{{CH}_{3} {CH}_{2} CHO} + 2 {[Ag {({NH}_{3})}_{2}]}^{+} + 3 {OH}^{-} \overset{}{\to} {CH}_{3} {CH}_{2} {COO}^{-} + Ag + 4 {NH}_{3} + 2 H_{2} O$

$\underset{Propanone}{{CH}_{3} {COCH}_{3}} + 2 {[Ag {({NH}_{3})}_{2}]}^{+} + 3 {OH}^{-} \overset{}{\to} No reaction$

(ii) Aldehydes respond to Fehling's test, but ketones do not.

Example: Propanal being an aldehyde reduces Fehling's solution to a red-brown precipitate of ${Cu}_{2} O$ , but propanone being a ketone does not.

$\underset{Propanal}{{CH}_{3} {CH}_{2} CHO} + 2 {Cu}^{2 +} + 5 {OH}^{-} \overset{}{\to} {CH}_{3} {CH}_{2} {COO}^{-} + {Cu}_{2} O + 3 H_{2} O$

$\underset{Propanone}{{CH}_{3} {COCH}_{3}} + 2 {Cu}^{2 +} + 5 {OH}^{-} \overset{}{\to} No reaction$

How aldehydes and ketones are distinguished? Give two chemical reactions.

Important Questions on Aldehydes, Ketones and Carboxylic Acids

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