Question

Which of the following compounds will give silver mirror with ammoniacal silver nitrate?
(A) Formic acid
(B) Formaldehyde
(C) Benzaldehyde
(D) Acetone
Choose the correct answer from the options given below :

• A. C and D only
• B. A, B and C only
• C. A only
• D. B and C only

Answer 1

The Correct Option is B

To identify compounds yielding a silver mirror with ammoniacal silver nitrate (Tollens' test), it's necessary to understand the test's chemical basis. This test detects aldehydes. During the reaction, aldehydes are oxidized to carboxylic acids, causing the silver ions in the reagent to reduce to metallic silver, forming a mirror on the test tube. Let's evaluate each compound:

1. Formic acid (A): Despite being a carboxylic acid, formic acid can yield a positive Tollens' test due to its facile oxidation to carbon dioxide and water, which precipitates silver.
2. Formaldehyde (B): As the simplest aldehyde, formaldehyde is readily oxidized by Tollens' reagent, resulting in a silver mirror.
3. Benzaldehyde (C): Benzaldehyde, also an aldehyde, will be oxidized to benzoic acid by Tollens' reagent, producing a silver mirror.
4. Acetone (D): Acetone is a ketone. Ketones typically do not react with Tollens' reagent because they are resistant to oxidation under these conditions; hence, no silver mirror will form.

Consequently, Formic acid (A), Formaldehyde (B), and Benzaldehyde (C) will produce a silver mirror with ammoniacal silver nitrate. The correct selection is:

A, B, and C only