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

To determine the number of S=O bonds present in each of the given acids, let's examine their molecular structures:

1. Sulphurous acid (H₂SO₃):
   • Structure: Sulphurous acid has one sulfur atom bonded to two hydroxyl groups (–OH) and double-bonded to one oxygen atom (S=O). It contains 1 S=O bond.
2. Peroxodisulphuric acid (H₂S₂O₈):
   • Structure: Peroxodisulphuric acid consists of two SO₃ groups connected by a peroxide linkage (–O–O–). Each SO₃ group has two S=O bonds, resulting in a total of 4 S=O bonds.
3. Pyrosulphuric acid (H₂S₂O₇):
   • Structure: Pyrosulphuric acid, also known as oleum, has two SO₃ units sharing an oxygen atom. Each SO₃ unit has two S=O bonds, resulting in a total of 4 S=O bonds.

With this detailed analysis, we find the number of S=O bonds in each compound:

• Sulphurous acid: 1 S=O bond
• Peroxodisulphuric acid: 4 S=O bonds
• Pyrosulphuric acid: 4 S=O bonds

Thus, the correct answer is 1, 4, and 4.