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Chapter 7: Problem 60

This section contains multiple choice questions. Each question has 4 choices (a), (b), (c) and (d), out of which ONLY ONE is correct. An ice cold solution of aniline in \(\mathrm{HCl}\) is treated with \(\mathrm{NaNO}_{2}\). The compound (A) thereby formed is tested for nitrogen using Lassaigne's test. The result would be (a) a Prussian blue colour confirming the presence nitrogen in aniline. (b) a green colour confirming the presence of nitrogen in aniline (c) an absence of any coloured solution to confirm the presence of nitrogen (d) evolution of ammonia which gives a colour with Nessler's reagent.

Short Answer

Expert verified
Answer: (c) An absence of any coloured solution to confirm the presence of nitrogen.

Step by step solution

01

Formation of Compound (A)

The first step is to create compound (A) by reacting aniline with HCl and NaNO2. Aniline reacts with HCl to form anilinium ion, which then reacts with NaNO2 to form diazonium chloride. Reaction: Aniline + HCl \(\rightarrow\) Anilinium ion Anilinium ion + NaNO2 \(\rightarrow\) Diazonium chloride Compound (A) = Diazonium chloride
02

Lassaigne's Test

Next, we will perform Lassaigne's test on compound (A). Lassaigne's test is a test used to detect the presence of nitrogen, halogens, and sulfur in an organic compound. When the compound is heated with molten sodium metal, it extracts these elements in the form of their respective sodium salts. Then, these resulting salts are dissolved in water and tested for the presence of nitrogen, halogens, and sulfur. In this case, we are specifically looking for the presence of nitrogen in the compound (A) after the reaction.
03

Expected Result with Lassaigne's Test

Lassaigne's test for nitrogen typically involves the formation of ferrocyanide complex ions (Prussian blue) when the dissolved salts are treated with FeSO4 and concentrated HCl. This complex forms only if the original compound contains nitrogen. However, diazonium chloride is not stable and decomposes into nitrogen gas and HCl, which then reacts with the sodium metal and does not form any colored complex. Reaction: Diazonium chloride \(\rightarrow\) N2 (gas) + HCl Nitrogen gas will not form any colored complex during the Lassaigne's test, and thus, the result would be an absence of any colored solution. So, the correct answer is (c) an absence of any coloured solution to confirm the presence of nitrogen.

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