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) \(\mathrm{Ag}_{2} \mathrm{SO}_{4}\) (d) \(\mathrm{H}_{2}\)

Short answer

Sulfur dioxide (SO_2) is evolved.

Step-by-step solution

Determine Reaction Type

The question involves a metal (silver) reacting with a concentrated acid (sulfuric acid). Such reactions are typically redox reactions, where metals like silver may reduce the sulfuric acid, leading to the evolution of a gas.

Identify Possible Reactions

When silver reacts with concentrated sulfuric acid, the reaction can produce silver sulfate (Ag_2SO_4) and a gas. Possible reactions can evolve gases such as sulfur dioxide (SO_2) rather than oxygen (O_2) or hydrogen (H_2).

Analyze Product Formation

In the reaction between silver and concentrated sulfuric acid, silver is oxidized and sulfur in H_2SO_4 is reduced. The reduction of H_2SO_4 results in the evolution of SO_2 gas. The reaction is: \[3Ag + 4H_2SO_4 \rightarrow Ag_2SO_4 + SO_2 + 2H_2O\]

Conclusion

Based on the above reaction, the gas evolved when silver reacts with concentrated sulfuric acid is sulfur dioxide (SO_2).

Key concepts

Silver and Sulfuric Acid Reaction

When silver is introduced to concentrated sulfuric acid, a fascinating chemical process unfolds. This reaction is characteristic of redox behavior, where electrons are transferred between the reacting substances. Here's what happens: silver (\( \text{Ag} \)) reacts with concentrated sulfuric acid (\( \text{H}_2\text{SO}_4 \)) to form silver sulfate (\( \text{Ag}_2\text{SO}_4 \)).
Simultaneously, a gas is evolved as part of the reaction process.
It is essential to understand that this is not just a simple combination of substances, but a transformation where silver acts as a reducing agent. The electron transfer transforms sulfuric acid into sulfur dioxide (\( \text{SO}_2 \)) gas. Sulfur dioxide is the pungent gas commonly associated with the smell of burning matchsticks or volcanic fumes.

• Silver sulfate formation: \( \text{Ag} + \text{H}_2\text{SO}_4 \rightarrow \text{Ag}_2\text{SO}_4 \)
• Gas evolved: \( \text{SO}_2 \)

This transformation showcases the dual role of sulfuric acid as both an oxidizer and a source material for compounds and gases.

Gas Evolution in Chemical Reactions

Gas evolution is a common phenomenon in certain chemical reactions.
The reaction between silver and sulfuric acid illustrates this well. When sulfuric acid reacts, it undergoes a reduction, liberating sulfur dioxide (\( \text{SO}_2 \)) as a gas.
The release of a gas is often a good indicator of a reaction taking place, and understanding the circumstances under which these gases evolve helps in comprehending the broader behavior of chemical reactions.

• Identifying evolution: In our case, the presence of sulfur dioxide signals a change in the substance state and energy within the system.
• Role of energy: The gas evolution also often involves the absorption or release of energy.
• Characteristic odor: Sulfur dioxide's pungent smell can be an immediate clue indicating its presence.

Recognizing these features aids in predicting reaction outcomes and is a practical skill in experimental chemistry.

Oxidation and Reduction

Oxidation and reduction reactions, or redox reactions, are fundamental to chemistry. In the reaction between silver and sulfuric acid, different elements undergo a change in their oxidation state.
Silver, as a reducing agent, gives up electrons—this process is known as oxidation.
Meanwhile, the sulfur in sulfuric acid accepts these electrons, known as reduction.
This electron transfer is central to many chemical processes, including the one where \( \text{SO}_2 \) gas evolved.

• Silver's role: Being oxidized from a metallic state, silver loses electrons and transforms.
• Sulfur's role: By accepting electrons, sulfur's oxidation state is reduced, showcasing its dual functionality in the reaction.
• Importance: Understanding electron movement can explain everything from energy changes to changes in the substance's physical state.

Mastering redox concepts is crucial for engaging with a wide range of chemical phenomena.