Question

Which of the following is the structure of pyrosulphuric acid?

• A. \( \text{HOO-S}(=\text{O})_2\text{-OH} \)
• B. \( \text{HO-S}(=\text{O})_2\text{-O-O-S}(=\text{O})_2\text{-OH} \)
• C. \( \text{O}^-\text{-S}(=\text{O})_2\text{-OH} \)
• D. \( \text{HO-S}(=\text{O})_2\text{-O-S}(=\text{O})_2\text{-OH} \)

Hint:

The prefix "pyro-" in inorganic acids indicates the loss of one water molecule from two molecules of the parent ortho-acid.
\[ 2\text{H}_2\text{SO}_4 \xrightarrow{-\text{H}_2\text{O}} \text{H}_2\text{S}_2\text{O}_7 \text{ (Pyrosulfuric acid)} \]
This dehydration creates the characteristic \( \text{S-O-S} \) anhydride bridge.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks to identify the correct chemical structure of pyrosulfuric acid (also known as disulfuric acid or oleum).

Step 2: Key Formula or Approach:
Pyrosulfuric acid has the chemical formula \( \text{H}_2\text{S}_2\text{O}_7 \). It consists of two sulfonic acid groups (\( -\text{SO}_3\text{H} \)) linked via a central oxygen atom forming an \( \text{S-O-S} \) bridge.

Step 3: Detailed Explanation:
Let's analyze the structures given in the options:
- Option (A): Represents peroxymonosulfuric acid (\( \text{H}_2\text{SO}_5 \), Caro's acid), which contains a peroxo (\( \text{-O-O-} \)) group.
- Option (B): Represents peroxodisulfuric acid (\( \text{H}_2\text{S}_2\text{O}_8 \), Marshall's acid), which has an \( \text{S-O-O-S} \) peroxide linkage.
- Option (C): Represents a bisulfate ion-like structure.
- Option (D): Shows two \( \text{-SO}_2\text{OH} \) groups sharing a central bridging oxygen atom (\( \text{S-O-S} \) linkage). This matches the formula \( \text{H}_2\text{S}_2\text{O}_7 \) and represents pyrosulfuric acid.

Step 4: Final Answer:
The correct structure of pyrosulfuric acid is shown in option (D).