Problem 61 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following gas is evolved when silver reacts with concentrated \(\mathrm{H}_{2} \mathrm{SO}_{4}\) ? (a) \(\mathrm{O}_{2}\) (b) \(\mathrm{SO}_{2}\) (c) \(\mathrm{Ag}_{7} \mathrm{SO}_{4}\) (d) \(\mathrm{H}_{2}\)

Step-by-Step Solution

Answer

(b) \(\mathrm{SO}_{2}\) gas is evolved.

Step 1: Identify Reactants and Products

When silver (Ag) reacts with concentrated \(\mathrm{H}_2 \mathrm{SO}_4\), it typically does not react unless high temperatures are applied. However, when it does react, silver sulfate (\(\mathrm{Ag}_2\mathrm{SO}_4\)) is typically one of the products, and a gas may be evolved.

Step 2: Analyze Possible Products

Once we know silver sulfate is a product, we observe that two other products are potentially formed: water (\(\mathrm{H}_2\mathrm{O}\)) and sulfur dioxide (\(\mathrm{SO}_2\)). Among the possible gases released during this reaction, sulfur dioxide is the most likely.

Step 3: Eliminate Incorrect Options

We can immediately eliminate options (a) \(\mathrm{O}_2\), and (c) \(\mathrm{Ag}_7\mathrm{SO}_4\), since these compounds are not gases produced in this type of reaction. Furthermore, hydrogen gas \(\mathrm{H}_2\) does not form by typical reactions with acids involving silver.

Step 4: Confirm the Correct Answer

Given the information and the chemical behavior of silver with \(\mathrm{H}_2 \mathrm{SO}_4\), the correct answer is that sulfur dioxide \(\mathrm{SO}_2\) gas is evolved in the reaction.

Key Concepts

Silver Reaction with Sulfuric Acid

When considering the reaction between silver (Ag) and sulfuric acid (\(\mathrm{H}_2\mathrm{SO}_4\)), it is essential to understand the conditions under which this reaction occurs. Silver is a relatively unreactive metal and does not easily react with dilute acids. However, when concentrated sulfuric acid and high temperatures combine, silver can react to form silver sulfate (\(\mathrm{Ag}_2\mathrm{SO}_4\)).

• Concentrated sulfuric acid acts as both a solvent and an oxidizing agent in this scenario.
• This reaction is uncommon as it typically requires heating to proceed.
• The presence of concentrated sulfuric acid is essential to facilitate the formation of silver sulfate.

Understanding this specific reaction offers insight into the broader category of metal-acid reactions and why certain conditions lead to varying reactivity.

Gas Evolution in Reactions

Gas evolution, a common occurrence in chemical reactions, involves the formation, release, and observation of a gas as a product. In the context of our reaction, the evolution of gas is a critical indicator of the completion of the chemical process.

• Gas evolution can provide visible clues that a reaction has occurred, such as bubbling or the emission of gas fumes.
• In this specific reaction, the production of sulfur dioxide (\(\mathrm{SO}_2\)) gas gives us direct evidence of the metal-sulfuric acid interaction.
• Observing gas evolution can be a tool in confirming the type of reaction and helping to identify the reaction products.

This understanding is not only crucial in laboratory settings for verifying reactions but also in industrial processes where gas evolution is a standard method for monitoring chemical production and progress.

Sulfur Dioxide Formation

Sulfur dioxide (\(\mathrm{SO}_2\)) formation is a result of the reaction between silver and concentrated sulfuric acid. Let's break down why \(\mathrm{SO}_2\) is evolved in this reaction:

• During this reaction, sulfuric acid acts as an oxidizing agent, facilitating the release of \(\mathrm{SO}_2\) gas.
• The decomposition of concentrated \(\mathrm{H}_2\mathrm{SO}_4\) under the reaction conditions contributes to \(\mathrm{SO}_2\) formation.
• The liberation of \(\mathrm{SO}_2\) is consistent with the reaction equation and expected chemical behavior.

Sulfur dioxide is a colorless gas with a pungent odor, commonly associated with acid rain. Understanding its formation is critical for handling chemical reactions that involve strong acids and metals, both for safety and industrial applications.