Problem 78 - A Complete Resource Book in Chemistry for JEE Main

Question

The acid having \(\mathrm{O}-\mathrm{O}\) bond is (a) \(\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\) (b) \(\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{6}\) (c) \(\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{8}\) (d) \(\mathrm{H}_{2} \mathrm{~S}_{4} \mathrm{O}_{6}\)

Step-by-Step Solution

Answer

Option (c) \( \mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{8} \) is the acid with an \( \mathrm{O}-\mathrm{O} \) bond.

Step 1: Analyze Option (a)

For the compound \( \mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{3} \) (thiosulfuric acid), its structure has each sulfur atom bonded to two oxygen atoms with no \( \mathrm{O}-\mathrm{O} \) bonds present. Hence, it is not the correct choice.

Step 2: Analyze Option (b)

The compound \( \mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{6} \) (dithionic acid) is analyzed. It features typical sulfur bonded to oxygen atoms but lacks an \( \mathrm{O}-\mathrm{O} \) bond, therefore, this is not the answer.

Step 3: Analyze Option (c)

The compound \( \mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{8} \) (peroxodisulfuric acid) is known to contain a \( \mathrm{O}-\mathrm{O} \) linkage, specifically a peroxo linkage, which distinguishes it as the correct choice.

Step 4: Analyze Option (d)

The compound \( \mathrm{H}_{2} \mathrm{~S}_{4} \mathrm{O}_{6} \) (tetrathionic acid) lacks an \( \mathrm{O}-\mathrm{O} \) bond between its atoms despite its complex structure. Thus, this is not the correct answer.

Key Concepts

Peroxodisulfuric Acid

Peroxodisulfuric acid, with the chemical formula \( \mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{8} \), contains a distinctive feature in its structure: an \( \mathrm{O}-\mathrm{O} \) linkage. This is referred to as a peroxo bond, which connects two oxygen atoms directly. This linkage is critical in distinguishing peroxodisulfuric acid from other sulfur-containing acids.

Peroxodisulfuric acid, also known as Marshall's acid, is an important oxidizing agent often used in the industry for various chemical processes. Its oxidizing strength is attributed to the peroxo group, making it useful for applications that require strong oxidizing conditions.

Remember, when you distinguish peroxodisulfuric acid from other similar compounds, always look for that characteristic \( \mathrm{O}-\mathrm{O} \) bond that sets it apart.

Dithionic Acid

Dithionic acid is represented by the formula \( \mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{6} \). In comparison to peroxodisulfuric acid, dithionic acid lacks the \( \mathrm{O}-\mathrm{O} \) bond, which is a key differentiator. Instead, in \( \mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{6} \), each sulfur atom is bonded to three oxygen atoms, and the sulfur atoms are linked to each other.

Despite dithionic acid not having the \( \mathrm{O}-\mathrm{O} \) bond, it’s still a noteworthy compound due to its own distinct structure with two linked sulfur centers. Though it's less commonly encountered than other sulfuric acids, it's a part of the diverse landscape of sulfur oxoacids and is sometimes used in specialized chemical procedures.

Thiosulfuric Acid

Thiosulfuric acid, with the formula \( \mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{3} \), adds another layer of variety to sulfuric acids. In its structure, it replaces one oxygen atom of sulfuric acid with a sulfur atom, hence the name 'thio' indicating the presence of extra sulfur.

Even though thiosulfuric acid doesn't contain an \( \mathrm{O}-\mathrm{O} \) bond, it features a unique makeup, having a sulfide linkage. It is relatively unstable compared to its counterparts and often decomposes under normal conditions. Thiosulfuric acid is mostly seen as its salts, such as thiosulfates, which are more stable and frequently used, especially in applications like photographic fixing.

Tetrathionic Acid

Tetrathionic acid, given by the formula \( \mathrm{H}_{2} \mathrm{~S}_{4} \mathrm{O}_{6} \), is even more complex, featuring a chain of four sulfur atoms. However, like thiosulfuric and dithionic acids, it does not possess an \( \mathrm{O}-\mathrm{O} \) bond. Instead, it showcases an intriguing arrangement of sulfur atoms linked together in a chain.

This acid is quite rare and is part of a larger group of polythionic acids. Although not commonly used in everyday chemical reactions, it demonstrates the diversity possible in sulfur compounds. Understanding these variations can deepen your insight into sulfur chemistry, revealing how different arrangements of atoms can lead to diverse chemical properties and uses.