ChemistryMediumClass 12

Sulphur Compounds — H₂S, SO₂, SO₃, H₂SO₄

p-block Elements (Class 12 — Groups 15, 16, 17, 18)

JEE Qs

Hard

105

min

Master the specific reaction conditions, catalysts, and distinct chemical properties (acidic, redox, dehydrating) of each sulphur compound to accurately predict reaction outcomes.

🧮 Key Formulas

FeS + 2HCl → FeCl₂ + H₂S

2H₂S + SO₂ → 3S + 2H₂O

Na₂SO₃ + H₂SO₄(dil) → Na₂SO₄ + H₂O + SO₂

S + O₂ → SO₂

SO₂ + Cl₂ + 2H₂O → H₂SO₄ + 2HCl

5SO₂ + 2KMnO₄ + 2H₂O → K₂SO₄ + 2MnSO₄ + 2H₂SO₄

2SO₂ + O₂ <=> 2SO₃ (V₂O₅ catalyst, 720K, 2 bar)

SO₃ + H₂SO₄(conc) → H₂S₂O₇ (Oleum)

H₂S₂O₇ + H₂O → 2H₂SO₄

Cu + 2H₂SO₄(conc, hot) → CuSO₄ + SO₂ + 2H₂O

C + 2H₂SO₄(conc, hot) → CO₂ + 2SO₂ + 2H₂O

C₁₂H₂₂O₁₁ + H₂SO₄(conc) → 12C + H₂SO₄·H₂O

✅ Key Points for JEE

1Sulphur exhibits multiple oxidation states (-2, +4, +6) in these compounds, dictating their redox properties (H₂S: strong reducing; SO₂: both reducing and oxidizing; SO₃, H₂SO₄: oxidizing).
2Understand the detailed conditions (catalyst, temperature, pressure) and intermediate steps (oleum formation) of the Contact Process for H₂SO₄ manufacturing.
3Distinguish the roles of concentrated H₂SO₄: strong acid, strong oxidizing agent (especially hot), and powerful dehydrating agent.
4Know the acidic nature of SO₂ (forms H₂SO₃) and SO₃ (forms H₂SO₄) and their reactions with bases.
5Be familiar with the molecular structures (e.g., bent for H₂S and SO₂, trigonal planar for SO₃) and associated VSEPR theory predictions.

⚠️ Common Mistakes

✕Confusing the specific oxidizing vs. reducing behavior of SO₂ and the conditions under which each occurs.
✕Incorrectly recalling the catalyst, temperature, or pressure requirements for the Contact Process or the reason for oleum formation.
✕Failing to recognize the distinct properties of H₂SO₄ (acidic, oxidizing, dehydrating) and applying the wrong property to a given reaction scenario.
✕Not predicting correct products for redox reactions involving sulphur compounds, especially with strong oxidizing/reducing agents.

NCERT Chapters

Class 12 Chemistry Ch 7: The p-Block Elements