Nitrogen (N2) for NEET: Key Points, Tricks & MCQs

What NEET Asks

• Direct questions on preparation methods (reagents, conditions, products of N2).
• Physical and chemical properties of N2, including inertness and high-temperature reactions.
• Assertion-Reason or Match-the-following questions based on N2 reactions and uses.

Key Points

• Dinitrogen (N2) constitutes ~78% of the atmosphere by volume.
• Lab preparation: Heating a mixture of aqueous NH4Cl and NaNO2 yields N2, NaCl, H2O. Traces of NO are removed by passing through H2SO4.
• Very pure N2: Obtained by thermal decomposition of barium azide [Ba(N3)2] or sodium azide [NaN3].
• Industrial preparation: Fractional distillation of liquid air, where N2 (b.p. -196°C) distills off first.
• Properties: Colorless, odorless, tasteless, non-toxic gas; very low solubility in water.
• Chemical inertness: N2 is relatively unreactive at room temperature due to the high bond dissociation enthalpy (941.4 kJ/mol) of the N≡N triple bond.
• Reactions at high temp: Reacts with active metals (e.g., Li, Mg, Al) to form nitrides, and with H2 (Haber process) and O2 (nitric oxide).
• Uses: Manufacture of ammonia, nitric acid, calcium cyanamide, providing an inert atmosphere, cryogenics.

Must-Know Formula / Reaction

• Lab Prep (from NH4Cl and NaNO2): NH4Cl (aq) + NaNO2 (aq) → N2(g) + 2H2O(l) + NaCl(aq)
• Very Pure N2 (from barium azide): Ba(N3)2(s) → Ba(s) + 3N2(g)
• Haber Process (Industrial synthesis of Ammonia): N2(g) + 3H2(g) ⇌ 2NH3(g) (Conditions: High temp ~700K, High pressure ~200 atm, Catalyst Fe/Mo)

Common Mistakes

• Students often confuse reagents for lab preparation vs. industrial preparation of N2.
• Don't mix up the products of thermal decomposition, e.g., (NH4)2Cr2O7 yields N2, while NH4NO3 yields N2O.
• Students sometimes overlook the inertness of N2 at room temperature and predict reactions readily without considering specific conditions.

Rapid Revision

N2 is prepared in the lab from NH4Cl/NaNO2 or very purely from Ba(N3)2. Industrially, it's from liquid air. Its inertness at room temp is due to the strong N≡N bond. It reacts at high temperatures (e.g., with H2 for NH3, with O2 for NO). Major uses include ammonia synthesis and creating inert atmospheres.