9.5 Sulphur :

Unit 9.5: Sulphur (5 Teaching Hours)

1. Allotropes of Sulphur (Name Only) and Uses

   • Allotropes
     • Rhombic Sulphur, Monoclinic Sulphur, Plastic Sulphur.
   • Uses of Sulphur
     • Manufacture of H₂SO₄, gunpowder, matches, and vulcanized rubber.
     • Fungicides, insecticides, and pharmaceuticals.

2. Hydrogen Sulphide (H₂S)

   • Preparation from Kipp’s Apparatus
     • Prepared by reacting FeS with dilute H₂SO₄ in Kipp’s apparatus: FeS + H₂SO₄ → FeSO₄ + H₂S.
     • Figure 1: Kipp’s Apparatus for H₂S Preparation (Diagram showing Kipp’s apparatus with FeS and H₂SO₄ setup).
   • Properties
     • Acidic Nature: Weak dibasic acid, forms sulphides: H₂S ⇌ H⁺ + HS⁻ ⇌ 2H⁺ + S²⁻.
     • Reducing Nature: Reduces halogens, HNO₃, and KMnO₄ (e.g., H₂S + I₂ → 2HI + S).
     • Analytical Reagent: Precipitates metal sulphides in qualitative analysis (e.g., Cu²⁺ forms CuS).
     • Figure 2: Structure of H₂S (Diagram showing bent structure of H₂S).
   • Uses
     • Analytical reagent in qualitative analysis for detecting metal ions.
     • Synthesis of sulphides and organosulphur compounds.

3. Sulphur Dioxide (SO₂)

   • Properties
     • Acidic Nature: Forms sulphurous acid with water: SO₂ + H₂O → H₂SO₃.
     • Reducing Nature: Reduces halogens, KMnO₄, and K₂Cr₂O₇ (e.g., SO₂ + 2KMnO₄ + 2H₂O → K₂SO₄ + 2MnSO₄ + 2H₂SO₄).
     • Oxidising Nature: Oxidises H₂S to sulphur: 2H₂S + SO₂ → 3S + 2H₂O.
     • Bleaching Action: Temporary bleaching by reduction (nascent hydrogen): SO₂ + 2H₂O → H₂SO₄ + 2[H].
     • Figure 3: Structure of SO₂ (Diagram showing bent structure of SO₂).
   • Uses
     • Manufacture of H₂SO₄ (contact process).
     • Bleaching agent for paper, textiles, and food preservation.
     • Disinfectant and fumigant.

4. Sulphuric Acid (H₂SO₄)

   • Properties
     • Acidic Nature: Strong dibasic acid, ionizes completely: H₂SO₄ → 2H⁺ + SO₄²⁻. Neutralizes bases (e.g., H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O).
     • Oxidising Nature: Conc. H₂SO₄ oxidises metals, non-metals: C + 2H₂SO₄ → CO₂ + 2SO₂ + 2H₂O.
     • Dehydrating Nature: Removes water from sugars, alcohols: C₆H₁₂O₆ → 6C + 6H₂O.
     • Figure 4: Structure of H₂SO₄ (Diagram showing tetrahedral structure of H₂SO₄).
   • Uses
     • Manufacture of fertilizers (e.g., ammonium sulphate).
     • Petroleum refining, detergents, and battery acid.
     • Dehydrating agent in organic synthesis.

5. Sodium Thiosulphate (Na₂S₂O₃)

   • Formula
     • Na₂S₂O₃
   • Uses
     • Photography (fixer to dissolve unexposed AgBr).
     • Titration (iodometric titrations to estimate iodine).
     • Antichlor to remove excess Cl₂ in bleaching.