Problem 118 - A Complete Resource Book in Chemistry for JEE Main

Question

In the following sequence of reactions, identify the end product (D). \(\mathrm{Na}_{2} \mathrm{CO}_{3} \stackrel{\mathrm{SO}_{2}}{\longrightarrow}(\mathrm{A}) \stackrel{\mathrm{Na}_{2} \mathrm{CO}_{3}}{\longrightarrow}(\mathrm{B})\) Elemental \(\mathrm{S} \stackrel{\Delta}{\longrightarrow}(\mathrm{C}) \stackrel{\mathrm{I}_{2}}{\longrightarrow}(\mathrm{D})\) (a) \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) (b) \(\mathrm{Na}_{2} \mathrm{~S}_{4} \mathrm{O}_{6}\) (c) \(\mathrm{Na}_{2} \mathrm{~S}\) (d) \(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\)

Step-by-Step Solution

Answer

The end product (D) is \( \mathrm{Na}_{2} \mathrm{S}_{2} \mathrm{O}_{3} \), option (d).

Step 1: Reaction of Na2CO3 with SO2

When sodium carbonate \( \mathrm{Na}_{2} \mathrm{CO}_{3} \) reacts with sulfur dioxide \( \mathrm{SO}_{2} \), it forms sodium sulfite \( \mathrm{Na}_{2} \mathrm{SO}_{3} \). This compound is classified as product (A) of the sequence.

Step 2: Reaction of Product (A) with Na2CO3

The new product \( \mathrm{Na}_{2} \mathrm{SO}_{3} \) (Product A) reacts with more \( \mathrm{Na}_{2} \mathrm{CO}_{3} \) forming sodium thiosulfate \( \mathrm{Na}_{2} \mathrm{S}_{2} \mathrm{O}_{3} \). This compound is identified as product (B) in the sequence.

Step 3: Heating Elemental Sulfur

Elemental sulfur \( \mathrm{S} \) when heated (denoted by \( \Delta \)) forms sulfur dioxide \( \mathrm{SO}_{2} \). Here in the sequence, \( \mathrm{SO}_{2} \) is labeled as product (C).

Step 4: Reaction of Product (C) with Iodine

Sulfur dioxide \( \mathrm{SO}_{2} \) (Product C) reacts with iodine \( \mathrm{I}_{2} \) to produce sulfur tetraoiodate \( \mathrm{I}_{2} \mathrm{O}_{6} \) and this is labeled as product (D). However in given choices, \( \mathrm{Na}_{2} \mathrm{S}_{2} \mathrm{O}_{3} \) is closest as it is used primarily in iodine reduction reactions.

Key Concepts

Inorganic Chemistry

Inorganic chemistry is a broad field that focuses on substances that do not belong to the domain of organic chemistry. This includes a vast array of compounds that are not based solely on carbon-hydrogen bonds. Within this field, chemists study elements and compounds such as metals, minerals, and other non-organic substances.
In the context of reaction mechanisms, inorganic chemistry examines how different compounds interact and transform, often involving ionic bonds and redox reactions. Understanding these transformations can help explain how substances change at the molecular level.

• Inorganic compounds can be simple salts like sodium chloride or more complex coordination compounds.
• They often participate in reactions that involve electron transfer, leading to oxidation and reduction.
• Many are involved in critical industrial processes, such as catalysis or the manufacture of materials.

These reactions are crucial in various applications, from industrial processes to environmental chemistry, providing insight into converting molecules to desired products. By exploring these concepts, students can gain a deeper appreciation for the intricate dance of atoms and molecules in the non-organic world.

Sodium Carbonate Reactions

Sodium carbonate, \(\mathrm{Na}_{2} \mathrm{CO}_{3}\), is a versatile compound commonly known as soda ash or washing soda. It readily participates in various reactions due to its basic nature.
In the sequence discussed, sodium carbonate reacts with sulfur dioxide (\(\mathrm{SO}_{2}\)) to form sodium sulfite (\(\mathrm{Na}_{2} \mathrm{SO}_{3}\)). This reaction showcases sodium carbonate's ability to neutralize acidic oxides, highlighting its role in buffering and neutralization processes.

• Sodium carbonate can act as a source of \(\mathrm{CO}_{3}^{2-}\), which readily reacts with acidic species, illustrating its utility in chemistry.
• The reaction further transforms into sodium thiosulfate (\(\mathrm{Na}_{2} \mathrm{S}_{2} \mathrm{O}_{3}\)), demonstrating its potential to participate in more complex chemical pathways.
• Sodium thiosulfate formed is known for its application in photographic processing and as a reducing agent in titration reactions, especially to gauge iodine concentration.

This adaptability makes sodium carbonate a critical reagent in various industrial and laboratory reactions, where it helps manage acidity and contribute to forming complex sulfur compounds.

Sulfur Chemistry

Sulfur chemistry is a fascinating area of inorganic chemistry involving the study of reactions and compounds of sulfur, a versatile and widespread element. Sulfur can exist in several oxidation states, making it highly reactive and capable of forming a variety of compounds.
In the exercise, sulfur undergoes oxidation when heated, forming sulfur dioxide (\(\mathrm{SO}_{2}\)), a key intermediate.

• This gas further reacts with basic compounds and elements, showcasing its versatility and reactivity.
• The transformation of elemental sulfur to \(\mathrm{SO}_{2}\) involves breaking the \(\mathrm{S}\) bonds and forming new \(\mathrm{S-O}\) bonds, indicative of oxidation.
• Sulfur dioxide, in further reaction, plays a crucial role in redox reactions, such as interacting with iodine to form sulfur tetraoiodate.

Understanding sulfur's ability to move between compounds and transformation, as shown in this exercise, is pivotal in grasping the broader scope of chemical reactions involving non-metallic elements. These principles are foundational in environmental chemistry, particularly in the study of atmospheric gases and industrial processes.