Question

Semicarbazide is commonly used to identify:

• A. Alcohols
• B. Carboxylic acids
• C. Aldehydes and ketones
• D. Amines

Hint:

Carbonyl compounds commonly form derivatives such as oximes, hydrazones, and semicarbazones for identification purposes.

Answer 1

The Correct Option is C

Concept: Semicarbazide reacts with carbonyl compounds such as aldehydes and ketones to form semicarbazones, which are crystalline derivatives useful for identification.

Step 1: Understanding semicarbazide.
Semicarbazide has the structure: \[ NH_2NHCONH_2 \] It reacts specifically with the carbonyl group: \[ >C=O \]

Step 2: Reaction with aldehydes and ketones.
Aldehydes and ketones contain carbonyl groups and therefore react with semicarbazide. For aldehydes: \[ RCHO + NH_2NHCONH_2 \rightarrow RCH=NNHCONH_2 \] For ketones: \[ RCOR' + NH_2NHCONH_2 \rightarrow RC=NNHCONH_2 \]

Step 3: Purpose of the reaction.
The semicarbazones formed are crystalline solids with definite melting points. These derivatives help chemists identify unknown aldehydes and ketones. Hence, semicarbazide is used for identifying: \[ \boxed{\text{Aldehydes and ketones}} \]