Question

Which of the following gives a Silver mirror test positively with Tollen's reagent?

• A. CH\(_3\)CH\(_2\)OH
• B. CH\(_3\)CHO
• C. CH\(_3\)COOH
• D. CH\(_3\)CH\(_2\)OCH\(_2\)CH\(_3\)

Hint:

Tollen's test and Fehling's test are the standard definitive reactions strictly identifying the presence of an aldehyde functional group ($-CHO$) over a ketone.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The Silver mirror test (Tollen's test) is a specific chemical laboratory test used to distinguish between aldehydes and ketones. It requires identifying the aldehyde among the given options.
Step 2: Detailed Explanation:
Tollen's reagent is an ammoniacal silver nitrate solution, $[Ag(NH_3)_2]^+$. It acts as a mild oxidizing agent.
- Aldehydes are readily oxidized to their corresponding carboxylic acids by Tollen's reagent. During this process, the $Ag^+$ ion is reduced to metallic silver ($Ag$), which deposits on the inner wall of the test tube, forming a shiny "silver mirror".
- Ketones, alcohols, ethers, and carboxylic acids generally resist oxidation by such a mild reagent and thus do not yield a positive test.
Let's look at the options:
(A) CH\(_3\)CH\(_2\)OH is Ethanol (a primary alcohol) - Negative.
(B) CH\(_3\)CHO is Acetaldehyde (an aldehyde) - Positive.
(C) CH\(_3\)COOH is Acetic acid (a carboxylic acid) - Negative.
(D) CH\(_3\)CH\(_2\)OCH\(_2\)CH\(_3\) is Diethyl ether (an ether) - Negative.
Therefore, acetaldehyde is the only compound that will form the silver mirror.
Step 3: Final Answer:
CH\(_3\)CHO gives a positive silver mirror test.