9.2 Nitrogen

Chemistry – Class 11

Reason for inertness of nitrogen and active nitrogen ; Chemical properties of ammonia [ Action with CuSO4 solution, water, FeCl3 solution, Conc. HCl, Mercurous nitrate paper, O2 ]; Applications of ammonia; Harmful effects of ammonia ; Oxy-acids of nitrogen (name andformula); Chemical properties of nitric acid [HNO3 as an acid and oxidizing agent (action with zinc, magnesium, iron, copper, sulphur, carbon, SO2 and H2S) ; Ring test for nitrate ion.

No MCQ questions available for this chapter.

Unit 9.2: Nitrogen (5 Teaching Hours)

  1. Reason for Inertness of Nitrogen and Active Nitrogen

    • Inertness of Nitrogen: Due to strong N≡N triple bond (bond energy ~945 kJ/mol), requiring high energy to break. Stable, non-reactive under normal conditions.
    • Active Nitrogen: Formed by electric discharge or high-energy conditions, making it reactive. Combines with metals (e.g., Mg, Na) to form nitrides or with O₂ to form nitric oxide (NO).

  2. Chemical Properties of Ammonia (NH₃)

    • Action with CuSO₄ Solution: Forms deep blue complex, [Cu(NH₃)₄]²⁺: CuSO₄ + 4NH₃ → [Cu(NH₃)₄]SO₄.
    • Action with Water: Weak base, forms ammonium hydroxide: NH₃ + H₂O ⇌ NH₄⁺ + OH⁻.
    • Action with FeCl₃ Solution: Forms brown precipitate of Fe(OH)₃: FeCl₃ + 3NH₃ + 3H₂O → Fe(OH)₃↓ + 3NH₄Cl.
    • Action with Conc. HCl: Forms white fumes of ammonium chloride: NH₃ + HCl → NH₄Cl.
    • Action with Mercurous Nitrate Paper: Turns black due to formation of mercury: Hg₂(NO₃)₂ + 2NH₃ → Hg + HgNH₂NO₃ + NH₄NO₃.
    • Action with O₂: Burns in presence of catalyst (Pt) to form NO: 4NH₃ + 5O₂ → 4NO + 6H₂O.

    • Figure 1: Structure of Ammonia Molecule (Diagram showing trigonal pyramidal structure of NH₃).

  3. Applications of Ammonia

    • Fertilizer production (e.g., urea, ammonium nitrate).
    • Manufacture of nitric acid (Ostwald process).
    • Used in refrigeration systems due to high heat of vaporization.
    • Synthesis of chemicals (e.g., explosives, dyes).

  4. Harmful Effects of Ammonia

    • Irritates eyes, skin, and respiratory system at high concentrations.
    • Toxic if inhaled in large amounts, causing lung damage.
    • Environmental pollution from ammonia leaks, contributing to acid rain.

  5. Oxy-Acids of Nitrogen (Name and Formula)

    • Nitrous Acid: HNO₂
    • Nitric Acid: HNO₃

    • Figure 2: Structures of HNO₂ and HNO₃ (Diagram showing molecular structures).

  6. Chemical Properties of Nitric Acid (HNO₃)

    • As an Acid
      • Strong monobasic acid, ionizes completely: HNO₃ → H⁺ + NO₃⁻.
      • Neutralizes bases to form nitrates: HNO₃ + NaOH → NaNO₃ + H₂O.
    • As an Oxidizing Agent
      • With Zinc: Forms different products based on HNO₃ concentration:
        • Dilute HNO₃: 4Zn + 10HNO₃ → 4Zn(NO₃)₂ + NH₄NO₃ + 3H₂O.
        • Conc. HNO₃: Zn + 4HNO₃ → Zn(NO₃)₂ + 2NO₂ + 2H₂O.
      • With Magnesium: Similar to Zn, forms nitrates and nitrogen oxides or NH₄NO₃.
      • With Iron: Passivates iron with conc. HNO₃ due to oxide layer; dilute HNO₃ produces Fe(NO₃)₂ and NO.
      • With Copper: Cu + 4HNO₃(conc.) → Cu(NO₃)₂ + 2NO₂ + 2H₂O; dilute forms NO.
      • With Sulphur: S + 6HNO₃ → H₂SO₄ + 6NO₂ + 2H₂O.
      • With Carbon: C + 4HNO₃ → CO₂ + 4NO₂ + 2H₂O.
      • With SO₂: SO₂ + 2HNO₃ → H₂SO₄ + 2NO₂.
      • With H₂S: H₂S + 2HNO₃ → S + 2NO₂ + 2H₂O.

    • Figure 3: Oxidation Reactions of HNO₃ (Diagram showing HNO₃ reacting with metals/non-metals).

  7. Ring Test for Nitrate Ion

    • Add FeSO₄ to nitrate solution, then slowly add conc. H₂SO₄ along the test tube wall.
    • Brown ring forms at the interface due to [Fe(H₂O)₅NO]²⁺: NO₃⁻ + 3Fe²⁺ + 4H⁺ → NO + 3Fe³⁺ + 2H₂O.

    • Figure 4: Brown Ring Test (Diagram showing test tube with brown ring).
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