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Chapter 7: Problem 113

Identify the wrong statement among the following (a) Molisch's test is used for the identification of carbohydrates. (b) Fehling solution \(A\) is an aqueous solution of \(\mathrm{CuSO} 4\). (c) Fehling solution \(\mathrm{B}\) is an alkaline solution of Rochelle salt. (d) All aldehydes reduce Fehling's solution to a red precipitate of Cu2O.

Short Answer

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(a) Molisch's test is used to detect the presence of carbohydrates. (b) Fehling solution A is an aqueous solution of CuSO4. (c) Fehling solution B is an alkaline solution containing Rochelle salt and a strong alkali. (d) All aldehydes reduce Fehling's solution to a red precipitate of Cu2O. Answer: (d) All aldehydes reduce Fehling's solution to a red precipitate of Cu2O.

Step by step solution

01

1. Information about Molisch's test

Molisch's test is a general test for carbohydrates. It indicates the presence of carbohydrates by forming a purple or violet ring at the junction when concentrated sulfuric acid is added to a solution containing carbohydrates. So, statement (a) is true.
02

2. Information about Fehling's solution A

Fehling solution A is an aqueous solution of copper(II) sulfate, represented by the chemical formula \(\mathrm{CuSO}_4\). Fehling solution A is blue in color. Thus, statement (b) is true.
03

3. Information about Fehling's solution B

Fehling solution B is an alkaline solution containing potassium sodium tartrate (also known as Rochelle salt) and a strong alkali - usually sodium hydroxide, NaOH. The chemical formula for Rochelle salt is KNaC\(_4\)H\(_4\)O\(_6\)·4H\(_2\)O. The purpose of Fehling solution B is to form a complex with Cu(II) ions, which causes the solution to be an effective oxidizing agent. So, statement (c) is true.
04

4. Information about the reactions of aldehydes with Fehling's solution

Aldehydes react with Fehling's solution, reducing it to a red precipitate of copper(I) oxide, \(\mathrm{Cu_2O}\). However, not all aldehydes can reduce Fehling's solution. Aromatic aldehydes (aldehydes with an aromatic ring in their structure) do not react with Fehling's solution, as it requires an alpha-hydrogen. Therefore, statement (d) is incorrect. Hence, the incorrect statement among the given options is: (d) All aldehydes reduce Fehling's solution to a red precipitate of Cu2O.

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