Problem 167 - A Complete Resource Book in Chemistry for JEE Main

Question

Which among the following are not peroxo acid of sulphur? (a) \(\mathrm{H}_{2} \mathrm{SO}_{4}\) (b) \(\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{8}\) (c) \(\mathrm{H}_{2} \mathrm{SO}_{3}\) (d) \(\mathrm{H}_{2} \mathrm{SO}_{5}\)

Step-by-Step Solution

Answer

The compounds not peroxo acids are (a) \(\mathrm{H}_{2} \mathrm{SO}_{4}\) and (c) \(\mathrm{H}_{2} \mathrm{SO}_{3}\).

Step 1: Define Peroxo Acid

A peroxo acid of sulphur contains an -S-O-O-H (peroxy) linkage in its structure. These are special types of sulphuric or sulphurous acids where an additional oxygen is bonded through a peroxide linkage.

Step 2: Analyze Each Compound

Now, let's analyze each given compound:(a) \(\mathrm{H}_{2} \mathrm{SO}_{4}\) - This is sulfuric acid and does not contain a peroxide linkage.(b) \(\mathrm{H}_{2} \mathrm{S}_{2} \mathrm{O}_{8}\) - Known as peroxydisulfuric acid, this contains the peroxy linkage.(c) \(\mathrm{H}_{2} \mathrm{SO}_{3}\) - This is sulfurous acid and does not contain a peroxide linkage.(d) \(\mathrm{H}_{2} \mathrm{SO}_{5}\) - Known as peroxymonosulfuric acid, this contains the peroxy linkage.

Step 3: Identify Non-Peroxo Acid Compounds

Among the given options, the compounds that do not have the peroxy linkage are not considered peroxo acids of sulphur. From the analysis, \(\mathrm{H}_{2} \mathrm{SO}_{4}\) and \(\mathrm{H}_{2} \mathrm{SO}_{3}\) lack the peroxo linkage.

Key Concepts

Sulfuric Acid

Sulfuric acid is one of the most important industrial chemicals and is often referred to by its chemical formula, \( \mathrm{H}_{2} \mathrm{SO}_{4} \). Widely used in many industries, it serves various purposes such as in the manufacture of fertilizers, cleaning agents, and in chemical synthesis.
Sulfuric acid consists of two hydrogen atoms, one sulfur atom, and four oxygen atoms. When dissolved in water, it releases two protons (\( \mathrm{H}^{+} \)), making it a strong acid. This means it can donate these hydrogen ions very easily, leading to its classification as a highly reactive acid.

• Does not contain a peroxide linkage
• Has a tetrahedral geometry
• Highly effective in dehydrating substances

Because it lacks the peroxy linkage, sulfuric acid is considered a simple acid rather than a peroxo acid. Understanding this difference is crucial when studying its behavior in chemical reactions.

Peroxide Linkage

Peroxide linkages are unique and important in the classification of peroxo acids. These linkages involve a bond between two oxygen atoms (\(-O-O-\)), creating a peroxide group. In the context of sulphur-based compounds, this linkage adds an additional dimension to their chemical structure.
In sulphur peroxo acids, the presence of an additional oxygen atom connected to sulfur through this linkage leads to different properties compared to non-peroxo acids.

• Creates a distinct class of sulphur acids
• Enhances the oxidative capabilities
• Gives peroxo acids unique reactivity

Understanding the characteristics of the peroxide linkage helps explain why peroxosulfuric acid compounds such as \( \mathrm{H}_{2} \mathrm{S}_{2} \mathrm{O}_{8} \) and \( \mathrm{H}_{2} \mathrm{SO}_{5} \) behave differently than standard sulfuric or sulfurous acids. This is especially important in applications where oxidative properties are required.

Sulfurous Acid

Sulfurous acid, represented by the chemical formula \( \mathrm{H}_{2} \mathrm{SO}_{3} \), is another important compound in the study of sulfur chemistry. It is typically encountered as an intermediate in the conversion of sulfur dioxide (\( \mathrm{SO}_{2} \)) to sulfuric acid.
It consists of two hydrogen atoms, one sulfur atom, and three oxygen atoms. Unlike sulfuric acid, sulfurous acid is a weak acid, meaning it does not completely dissociate in solution.

• Lacks peroxide linkage
• Exists in aqueous situations as a solution
• Known for its role in wine preservation due to its sulfite content

Since sulfurous acid does not have the peroxy linkage, it does not fall under the category of peroxo acids. Understanding sulfurous acid's structure and lack of peroxide linkage is essential for correctly classifying these compounds.