Chapter 4: Group V-A and Group VI-A Elements

Includes Nitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb), Bismuth (Bi).

• General Trends: ns²np³ configuration. N and P are non-metals, As and Sb are metalloids, Bi is metal.
• Nitrogen vs Others: N is gas, diatomic (N2), inert at room temp, forms pπ-pπ multiple bonds. Others are solids, polyatomic (P4), reactive.

Oxides

• Dinitrogen Oxide (N2O): Laughing gas. Colorless, fair smell. Prepared by heating NH4NO3.
• Nitric Oxide (NO): Colourless gas. Turns brown (NO2) in air. Preparation: Cu + dil.HNO3.
• Nitrogen Dioxide (NO2): Reddish brown, pungent. Dimerizes to colorless N2O4 on cooling. Preparation: Pb(NO3)2 heat.

Nitric Acid (HNO3)

• Preparation (Birkeland & Eyde): N2 + O2 → NO → NO2 → HNO3 (Electric Arc).
• Properties: Strong acid, strong oxidizing agent. Soluble in water.
• Reactions:
  • Cu + dil. HNO3: NO gas.
  • Cu + conc. HNO3: NO2 gas.
  • Aqua Regia: 1 part conc. HNO3 + 3 parts conc. HCl. Dissolves Au/Pt by forming nascent chlorine.
• Ring Test: For nitrates. FeSO4 + NO → [Fe(NO)]SO4 (Brown ring).

Allotropes

• White P: Tetrahedral P4, waxy, poisonous, very reactive, phosphorescence.
• Red P: Polymer chain, less reactive, non-poisonous.

Compounds

• Halides: PCl3 and PCl5.
• Oxides: P2O3 (from limited air) and P2O5 (from excess air). P2O5 is strong dehydrating agent.
• Orthophosphoric Acid (H3PO4): Preparation: P2O5 + Hot H2O. Weak tribasic acid.

Includes Oxygen (O), Sulphur (S), Selenium (Se), Tellurium (Te), Polonium (Po).

• General Trends: ns²np⁴ configuration. O, S are non-metals.
• Oxygen vs Sulphur: O is gas (O2), H-bonding in water. S is solid (S8), no H-bonding in H2S.

Contact Process

1. Sulphur Burner: S + O2 → SO2.
2. Purifying Unit: Remove dust, Arsenic (catalyst poison) using Fe(OH)3.
3. Contact Tower: 2SO2 + O2 ⇌ 2SO3. Catalyst: V2O5 at 400-500°C.
4. Absorption: SO3 + H2SO4 → H2S2O7 (Oleum). Then Oleum + H2O → H2SO4.

Properties

• Dehydrating Agent: Removes water from sugar (chars to C), formic acid (CO), oxalic acid.
• Oxidizing Agent: Oxidizes C to CO2, S to SO2.
• Reactions with Metals: Cu + conc. H2SO4 → CuSO4 + SO2 + H2O.