Problem 113 - A Complete Resource Book in Chemistry for JEE Main

Question

\([\mathrm{X}]+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow[\mathrm{Y}]\), a colourless gas with irritating smell. \([\mathrm{Y}]+\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow\) green solution. \([\mathrm{X}]\) and \([\mathrm{Y}]\) are (a) \(\mathrm{SO}_{3}^{-2}, \mathrm{SO}_{2}\) (b) \(\mathrm{Cl}^{-}, \mathrm{HCl}\) (c) \(\mathrm{S}^{-2}, \mathrm{H}_{2} \mathrm{~S}\) (d) \(\mathrm{CO}_{3}^{-2}, \mathrm{CO}_{2}\)

Step-by-Step Solution

Answer

The correct answer is (a) \( \text{SO}_3^{2-}, \text{SO}_2 \).

Step 1: Identify X and Y

We need to identify substances X and Y based on the reactions and options provided. In the first reaction, X reacts with sulfuric acid to produce Y, a colorless gas with an irritating smell. In the second reaction, Y reacts with potassium dichromate and sulfuric acid to form a green solution.

Step 2: Analyze Reaction 1

Examine the options and identify which anion, when reacted with sulfuric acid, produces a colorless gas with an irritating smell. Option (a) suggests \( \text{SO}_3^{2-}\) produces \( \text{SO}_2\), which is a colorless gas with an irritating smell. This matches the description of Y.

Step 3: Analyze Reaction 2

Verify if the gas produced, \( \text{SO}_2 \), reacts with potassium dichromate and sulfuric acid to produce a green solution. Sulfur dioxide is known to turn potassium dichromate green, confirming that Y is indeed \( \text{SO}_2 \).

Step 4: Eliminate Incorrect Options

Check other options: b) \( \text{Cl}^- \) forming \( \text{HCl} \) - HCl doesn't result in a green solution.c) \( \text{S}^{2-} \) forming \( \text{H}_2\text{S} \) – H2S doesn't react to form a green solution.d) \( \text{CO}_3^{2-} \) forming \( \text{CO}_2 \) – CO2 doesn't result in a green solution. Thus, these options can be eliminated.

Step 5: Confirm Correct Answer

Given that the reactions align with the description for X = \( \text{SO}_3^{2-} \) and Y = \( \text{SO}_2 \), match these with the available options. Option (a) \( (\text{SO}_3^{2-}, \text{SO}_2) \) correctly fits both the reactions and the descriptions.

Key Concepts

Inorganic Chemistry

Inorganic chemistry focuses on the properties and behavior of inorganic substances, including metals, minerals, and organometallic compounds. In contrast to organic chemistry, which deals mainly with carbon-based compounds, inorganic chemistry has a much broader scope that encompasses a wide range of compounds.
What's fascinating is that inorganic chemistry significantly contributes to various fields, such as materials science, catalysis, and energy production. In this context, we explore reactions involving non-carbon-based components like sulfur compounds and their interaction with various reagents.
Understanding inorganic reactions and their mechanisms is crucial for advancements in chemistry and in developing new industrial processes. With sulfur being a key player, inorganic chemistry helps explain its diverse reactions and formations in different environmental conditions.

Sulfur Compounds

Sulfur compounds play an essential role in various chemical reactions. These compounds range from simple sulfides to complex organic molecules containing sulfur. They are widely studied due to their importance in fields such as environmental science, biology, and medicine.
One important sulfur compound is sulfur dioxide \(\text{SO}_2\), typically formed from the oxidation of sulfite \(\text{SO}_3^{2-}\). This particular compound is known for its distinct pungent smell, which makes it significant in identifying specific reactions. In industrial settings, sulfur dioxide is used in the manufacture of sulfuric acid and as a preservative and antioxidant in the food industry.
In chemical reactions, sulfur dioxide serves as a reducing agent, especially evident when it interacts with oxidizing agents like potassium dichromate \(\text{K}_2\text{Cr}_2\text{O}_7\). These compounds highlight sulfur's versatility and its ability to participate in multiple reaction pathways.

Reaction Mechanics

Understanding reaction mechanics is fundamental in predicting the outcomes of chemical reactions. Reaction mechanics involve studying the process by which chemicals interact, the transformation of reactants into products, and the energy changes involved.
An example includes the reaction of sulfite \(\text{SO}_3^{2-}\) with sulfuric acid \(\text{H}_2\text{SO}_4\) to form sulfur dioxide \(\text{SO}_2\). In this process, the sulfur atom undergoes a change in oxidation state, playing a crucial role in the mechanics of the reaction.
Furthermore, when sulfur dioxide reacts with potassium dichromate in the presence of sulfuric acid, the solution's color change to green indicates an interplay of redox reactions. Tracking these reaction paths helps scientists develop efficient catalytic processes and understand the fundamental principles governing chemical transformations.

Anion Identification

Anion identification is a key skill in chemistry, essential for analyzing chemical reactions and determining substances present in a solution.
An example is identifying the anion \(\text{SO}_3^{2-}\) based on its reaction with sulfuric acid to produce \(\text{SO}_2\), a colorless gas with a characteristic irritating smell. This type of deduction uses the properties of substances to determine the possible identity of unknown components.
In the context of the exercise discussed, anion identification involves choosing from various options the correct anion that aligns with observed chemical behavior, such as changes in color, gas emission, or reaction with other compounds. Developing the ability to identify and verify anions through experimentation and observation is crucial for any aspiring chemist to accurately conduct analyses and predict chemical changes.