Question

What is the oxidation number of S in H₂S₂O₈ ?

• A. +5
• B. +4
• C. +7
• D. +6

Answer 1

The Correct Option is D

We are asked to find the oxidation number of sulfur (S) in the compound H₂S₂O₈ (Peroxodisulfuric acid).

Step-by-Step Solution: 

Step 1: Let the oxidation number of sulfur (S) be x.

Step 2: Oxidation number of hydrogen (H) is +1.

Step 3: Oxidation number of oxygen (O) is usually -2, but in peroxo linkages, it is -1.

Note: H₂S₂O₈ (peroxodisulfuric acid) contains a peroxo linkage (–O–O–), having two oxygen atoms with an oxidation number of -1.

Structure can be represented as: HO–SO₂–O–O–SO₂–OH

• 2 hydrogen atoms: each (+1) ⇒ total = +2
• 2 sulfur atoms: each = x ⇒ total = 2x
• 6 normal oxygen atoms (not in peroxo linkage): each (-2) ⇒ total = -12
• 2 peroxo oxygen atoms: each (-1) ⇒ total = -2

Step 4: The total charge on H₂S₂O₈ is zero, thus:

\[ (+2) + (2x) + (-12) + (-2) = 0 \]

Simplifying, we get:

\[ 2x - 12 = 0 \]

\[ 2x = +12 \]

\[ x = +6 \]

Conclusion:

The oxidation number of sulfur (S) in H₂S₂O₈ is +6.

Correct Answer: Option (D): +6