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 determine which of the given compounds will give a silver mirror with ammoniacal silver nitrate, we need to understand the chemistry behind the Tollens' test. This test is used to identify aldehydes. When aldehydes react with Tollens' reagent, which is a solution of ammoniacal silver nitrate, they are oxidized to carboxylic acids, and the reagent forms a silver mirror on the test tube as metallic silver is precipitated. Let's analyze each compound given:

1. Formic acid (A): Formic acid is capable of giving a positive Tollens' test, even though it is not an aldehyde. This is because formic acid is easily oxidized to carbon dioxide and water, producing a silver mirror in the process.
2. Formaldehyde (B): Being a simple aldehyde, formaldehyde readily undergoes oxidation with Tollens' reagent, forming a silver mirror. Therefore, formaldehyde will give a positive Tollens' test.
3. Benzaldehyde (C): Benzaldehyde is also an aldehyde, and it will be oxidized to benzoic acid by the Tollens' reagent, producing a silver mirror. Thus, it also gives a positive tollens test.
4. Acetone (D): Acetone is a ketone, and ketones generally do not react with Tollens' reagent because they are not oxidizable under the conditions of the test. Hence, acetone will not give a silver mirror.

Based on the analysis above, the correct compounds that will give a silver mirror with ammoniacal silver nitrate are Formic acid (A), Formaldehyde (B), and Benzaldehyde (C). Therefore, the correct answer is:

A, B, and C only

Answer 2

To determine which compounds will give a silver mirror with ammoniacal silver nitrate, we need to consider the Tollens' test. This test is generally used to identify aldehydes. The Tollens' reagent, which contains ammoniacal silver nitrate, oxidizes aldehydes to carboxylic acids, and in the process, the silver ion is reduced to metallic silver, forming a silver mirror on the inner walls of the test tube.

1. Formic acid (HCOOH) is an exception in this context. Although it is a carboxylic acid, it also acts as a reducing agent and can reduce Tollens' reagent to produce a silver mirror. Therefore, formic acid will give a silver mirror with ammoniacal silver nitrate.
2. Formaldehyde (HCHO) is the simplest aldehyde, and it will be oxidized by Tollens' reagent, thereby giving a silver mirror.
3. Benzaldehyde (C₆H₅CHO) is an aromatic aldehyde, and it also reacts with Tollens' reagent to produce a silver mirror.
4. Acetone (CH₃COCH₃) is a ketone. Ketones generally do not react with Tollens' reagent to form a silver mirror because they do not have a hydrogen atom bonded to the carbonyl carbon, which is necessary for the oxidation reaction to occur.

Therefore, the compounds that will give a silver mirror with ammoniacal silver nitrate are Formic acid, Formaldehyde, and Benzaldehyde. Thus, the correct answer is:

A, B, and C only