Question

Which of the following gives the silver mirror test?
A. Formic acid
B. \[C{H_3}COCHOHC{H_3}\]
C. Tartaric acid
D. Glucose

Answer 1

Hint: Silver mirror test is also termed as Tollens test. This test is used to differentiate between aldehydic group-containing compounds and ketonic group-containing compounds.

Complete Step by Step Solution:
Tollens reagent is a chemical reagent which helps in detecting the presence of an aldehyde functional group in the compound, alpha hydroxy ketone functional group in a compound and formic acid where its COOH group behaves like an aldehydic group.
The Tollens reagent is given by a German chemist known Bernhard Tollens. It is a solution mixture of silver nitrate and ammonia.

The compound gives a white precipitate of silver where silver salt reduces to silver metal and the aldehydic group get oxidises to silver salt of carboxylic acid.
A. Formic acid gives a positive silver mirror test as its COOH group act as an aldehydic group.

B. \[C{H_3}COCHOHC{H_3}\] has chemical name 3-hydroxybutan-2-one. It has an alpha hydroxy ketone functional group so it will give a positive silver mirror test.

C. Tartaric acid contains a COOH group which acts as an aldehydic group therefore it will give a silver mirror test.

Image: Tartaric acid

D. Glucose contains alpha hydroxy ketone functional group so it will give a positive silver mirror test.

Image: Glucose
Thus, options A, B, C and D are correct.

Note: Ketone does not give a silver mirror test but alpha hydroxy ketone gives a silver mirror test. An alpha hydroxy ketone is a molecule having adjacent ketone and alcohol groups. Example: Glucose, tartaric acid.