Problem 1 - A Complete Resource Book in Chemistry for JEE Main

Question

In Carius tube, the compound \(\mathrm{ClCH}_{2} \mathrm{COOH}\) was heated with fuming \(\mathrm{HNO}_{3}\) and \(\mathrm{AgNO}_{3}\). After filtration and washing, a white precipitate was formed. The precipitate is (a) \(\mathrm{Ag}_{2} \mathrm{SO}_{4}\) (b) \(\mathrm{AgNO}_{3}\) (c) \(\mathrm{AgCl}\) (d) \(\mathrm{ClCH}_{2} \mathrm{COOAg}\)

Step-by-Step Solution

Answer

The white precipitate is \( \mathrm{AgCl} \).

Step 1: Understand the Reaction Context

The Carius tube method involves degrading the compound using fuming nitric acid and silver nitrate, which often precipitates silver salts. Here, the compound is chlorinated acetic acid.

Step 2: Consider the Decomposition

The compound \( \mathrm{ClCH}_{2} \mathrm{COOH} \) will react with \( \mathrm{HNO}_{3} \) to break down, primarily affecting the chlorine atom bonded to carbon, often leading to halide formation like \( \mathrm{Cl}^- \).

Step 3: Precipitation of Silver Compounds

The \( \mathrm{AgNO}_3 \) in the reaction will react with ions formed from the chloride ion attack, notably \( \mathrm{Cl}^- \), precipitating \( \mathrm{AgCl} \), which is a common white precipitate.

Step 4: Analyze the Options

Consider the potential precipitates:\( \mathrm{AgCl} \) is a classic result from reactions involving chlorides; \( \mathrm{Ag}_2 \mathrm{SO}_4 \) requires sulfate ions, which are not present; \( \mathrm{AgNO}_3 \) is a reagent, not a precipitate; and \( \mathrm{ClCH}_{2} \mathrm{COOAg} \) requires a different reaction mechanism.

Step 5: Conclude with the Correct Answer

Since chloride ions are released and will form \( \mathrm{AgCl} \) with silver nitrate, the white precipitate is \( \mathrm{AgCl} \).

Key Concepts

Halide Precipitation

In chemistry, the process of halide precipitation occurs when halide ions, such as chlorides, react with certain reagents to form solid compounds, known as precipitates. These are typically insoluble in water and fall out of solution. This phenomenon is particularly useful for detecting the presence of specific halide ions in a mixture.
One of the most common reagents used for halide precipitation is silver nitrate (\(\mathrm{AgNO}_3\)). When halide ions like chloride (\(\mathrm{Cl}^-\)), bromide (\(\mathrm{Br}^-\)), or iodide (\(\mathrm{I}^-\)) react with \(\mathrm{AgNO}_3\), they form corresponding silver halides such as \(\mathrm{AgCl}\), \(\mathrm{AgBr}\), or \(\mathrm{AgI}\). These compounds appear as fine solids that can be filtered out from the reaction mixture.
When conducting experiments involving chlorinated organic compounds and silver nitrate, the formation of a white precipitate indicates the presence of chloride ions, confirming the occurrence of halide precipitation. This straightforward method is widely used in lab settings for both qualitative and quantitative analysis of halides.

Silver Nitrate Reaction

Silver nitrate (\(\mathrm{AgNO}_3\)) is a versatile reagent that plays a crucial role in various chemical reactions. It is especially known for its application in preparing silver halides, which are compounds formed when silver ions from \(\mathrm{AgNO}_3\) react with halide ions.
This process starts when silver nitrate is introduced into a solution containing halide ions. Upon interaction, silver ions (\(\mathrm{Ag}^+\)) form a solid precipitate with the halide ions present. This reaction is usually rapid and highly specific, making it easy to identify halides based on the nature of the precipitate formed. For instance, a white precipitate of \(\mathrm{AgCl}\) confirms the presence of chloride ions.
The appeal of using silver nitrate in experiments lies in its ability to create visible changes in mixtures, allowing scientists to confirm the occurrence of particular reactions. These silver halide reactions not only verify the presence of certain ions but also help in refining the understanding of compound behavior in different experimental scenarios.

Organic Compound Degradation

Degradation of organic compounds is a fundamental concept in chemistry, particularly when analyzing complex organic structures. It involves breaking down a compound into simpler components, often through chemical reactions that affect specific bonds within the molecule.
The Carius tube method is one classic way to achieve such degradation, especially for the analysis of chloro-organic compounds. This method uses fuming nitric acid and a metal nitrate, such as silver nitrate, to degrade the compound. In our example, chlorinated acetic acid (\(\mathrm{ClCH}_{2}\mathrm{COOH}\)) undergoes degradation, where the chlorine-carbon bond is cleaved.
During this process, chlorine is converted into a chloride ion (\(\mathrm{Cl}^-\)), which subsequently reacts with silver nitrate to form the precipitate silver chloride (\(\mathrm{AgCl}\)). The degradation not only facilitates the study of these specific ionic interactions but also reveals insights into the structural relationships within organic compounds, making it an indispensable tool in organic chemistry.