Question

The number of S=O bonds present in sulphurous acid, peroxodisulphuric acid and pyrosulphuric acid, respectively are :

• A. 2, 4 and 3
• B. 1, 4 and 4
• C. 1, 4 and 3
• D. 2, 3 and 4

Hint:

Draw the structure by placing S at the center. Use the rule: each S in high oxidation states (\(+4, +6\)) tries to form as many double bonds with Oxygen as possible, while satisfying the number of available Hydrogen atoms as -OH groups.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
To find the number of \( S=O \) bonds, we must look at the chemical structures of the oxoacids of sulphur.
Step 2: Detailed Explanation:
1. **Sulphurous acid (\( \text{H}_2\text{SO}_3 \)):** The structure is \( \text{O=S(OH)}_2 \). There is only **1** \( S=O \) bond.
2. **Peroxodisulphuric acid (\( \text{H}_2\text{S}_2\text{O}_8 \)):** Also known as Marshall's acid. Its structure is \( \text{(HO)S(=O)}_2\text{-O-O-S(=O)}_2\text{(OH)} \). Each Sulphur atom has two \( S=O \) bonds. Total \( S=O \) bonds = \( 2 + 2 = \) **4**.
3. **Pyrosulphuric acid (\( \text{H}_2\text{S}_2\text{O}_7 \)):** Also known as Oleum. Its structure is \( \text{(HO)S(=O)}_2\text{-O-S(=O)}_2\text{(OH)} \). Like Marshall's acid, it has two \( S=O \) bonds per Sulphur atom. Total \( S=O \) bonds = \( 2 + 2 = \) **4**.
Therefore, the counts are 1, 4, and 4.
Step 3: Final Answer:
The number of S=O bonds is 1, 4 and 4 respectively.