Nitrogen and its Compounds — Revision Notes

⚡ 30-Second Revision

Dinitrogen ($N_2$) — Inert due to $N equiv N$ bond. Lab prep: $NH_4Cl + NaNO_2 xrightarrow{\text{heat}} N_2$. Industrial: Fractional distillation of liquid air.
Ammonia ($NH_3$) — Pyramidal, $sp^3$ N. Lewis base. Haber process: $N_2 + 3H_2 \rightleftharpoons 2NH_3$ (Fe catalyst, $450-500^circ C$, $200,\text{atm}$). Forms complexes (e.g., $[Cu(NH_3)_4]^{2+}$).
Oxides of Nitrogen

- $N_2O$: +1, colorless, neutral, diamagnetic. - $NO$: +2, colorless, neutral, paramagnetic, oxidizes to $NO_2$ in air. - $N_2O_3$: +3, blue solid, acidic, unstable. - $NO_2$: +4, reddish-brown, acidic, paramagnetic, dimerizes to $N_2O_4$. - $N_2O_4$: +4, colorless, diamagnetic, dimer of $NO_2$. - $N_2O_5$: +5, colorless solid, acidic, strong oxidizing agent.

Nitric Acid ($HNO_3$) — Strong acid, powerful oxidizing agent. Ostwald process: $NH_3 xrightarrow{O_2, Pt/Rh} NO xrightarrow{O_2} NO_2 xrightarrow{H_2O, O_2} HNO_3$.

- Reactions with metals: Dilute $HNO_3 \rightarrow NO$; Conc. $HNO_3 \rightarrow NO_2$. Passivity with Fe, Cr, Al.

2-Minute Revision

Nitrogen, as $N_2$, is inert due to its strong triple bond, but its compounds are highly reactive and essential. Ammonia ($NH_3$) is a key compound, industrially produced by the Haber process using an iron catalyst at high pressure and moderate temperature.

Ammonia is a weak base, forms complexes with metal ions due to its lone pair, and has a trigonal pyramidal structure. Nitrogen forms a series of oxides, each with distinct properties and oxidation states: $N_2O$ (+1, laughing gas), $NO$ (+2, colorless, paramagnetic, turns brown in air), $N_2O_3$ (+3, blue solid), $NO_2$ (+4, reddish-brown, paramagnetic, dimerizes), $N_2O_4$ (+4, colorless dimer), and $N_2O_5$ (+5, strong oxidizing agent).

Nitric acid ($HNO_3$) is a strong oxidizing acid, manufactured via the Ostwald process. Its reactions with metals are concentration-dependent, yielding $NO$ with dilute acid and $NO_2$ with concentrated acid.

Remember the passivity of Fe, Cr, Al with concentrated $HNO_3$. Focus on balanced equations, reaction conditions, and distinguishing features for NEET.

5-Minute Revision

Begin your revision with elemental nitrogen ($N_2$). Recall its inertness due to the $N equiv N$ triple bond and its industrial preparation by fractional distillation of liquid air. The laboratory method involves heating $NH_4Cl$ with $NaNO_2$.

Next, move to ammonia ($NH_3$). Understand its pyramidal structure and $sp^3$ hybridization. The Haber process is critical: $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$, catalyzed by iron at $450-500^circ C$ and $200,\text{atm}$.

Ammonia's basic nature (Lewis base, Brønsted-Lowry base) and its ability to form deep blue complexes with $Cu^{2+}$ ions are important.

Then, tackle the oxides of nitrogen. Systematically review each: $N_2O$ (+1, colorless, neutral, diamagnetic); $NO$ (+2, colorless, paramagnetic, reacts with $O_2$ to form reddish-brown $NO_2$); $N_2O_3$ (+3, blue solid, unstable); $NO_2$ (+4, reddish-brown, paramagnetic, dimerizes to colorless $N_2O_4$); $N_2O_4$ (+4, colorless, diamagnetic); and $N_2O_5$ (+5, strong oxidizing agent, anhydride of $HNO_3$). Pay attention to their colors, magnetic properties, and acidic/neutral character.

Finally, focus on nitric acid ($HNO_3$). It's a strong acid and a powerful oxidizing agent. The Ostwald process is its industrial synthesis: $NH_3 xrightarrow{Pt/Rh, O_2} NO xrightarrow{O_2} NO_2 xrightarrow{H_2O, O_2} HNO_3$.

Crucially, memorize its reactions with metals: dilute $HNO_3$ typically yields $NO$ (e.g., with Cu), while concentrated $HNO_3$ yields $NO_2$ (e.g., with Cu). Remember the passivity of Fe, Cr, and Al with concentrated $HNO_3$ due to oxide layer formation.

Practice balancing these redox reactions. Ensure you can assign oxidation states for nitrogen in all these compounds and understand their molecular geometries.

Prelims Revision Notes

Nitrogen and its Compounds: NEET Revision Notes

1. Dinitrogen ($N_2$)

Occurrence — 78% of atmosphere.
Bonding — Strong $N equiv N$ triple bond (high bond enthalpy, $941.4,\text{kJ/mol}$), making it inert at room temperature.
Lab Prep — $NH_4Cl(aq) + NaNO_2(aq) xrightarrow{\text{heat}} N_2(g) + 2H_2O(l) + NaCl(aq)$.
Industrial Prep — Fractional distillation of liquid air (N.P. $77.2,\text{K}$, O.P. $90,\text{K}$).
Properties — Colorless, odorless, tasteless, non-toxic, sparingly soluble in water. Reacts with active metals (e.g., Li, Mg) and non-metals (H, O) at high temperatures.
Uses — Inert atmosphere, cryogenics, ammonia synthesis.

2. Ammonia ($NH_3$)

Structure — Trigonal pyramidal, $sp^3$ hybridized N, bond angle $approx 107^circ$ (due to lone pair repulsion).
Lab Prep — Heating ammonium salts with strong base, e.g., $2NH_4Cl + Ca(OH)_2 xrightarrow{\text{heat}} CaCl_2 + 2NH_3 + 2H_2O$.
Industrial Prep (Haber Process) — $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$ ($Delta H = -92.4,\text{kJ/mol}$).

* Conditions: Fe catalyst (with $K_2O/Al_2O_3$ promoters), $450-500^circ C$, $200,\text{atm}$. * Principle: Le Chatelier's principle (exothermic, decrease in moles of gas).

Properties — Pungent gas, highly soluble in water (H-bonding).

* Basic Nature: Lewis base (lone pair), Brønsted-Lowry base (accepts $H^+$). Forms $NH_4OH$ in water. * Complex Formation: Ligand, forms complexes with transition metal ions (e.g., $[Cu(NH_3)_4]^{2+}$ deep blue). * Reducing Agent: $3CuO + 2NH_3 xrightarrow{\text{heat}} 3Cu + N_2 + 3H_2O$. * Oxidation: $4NH_3 + 5O_2 xrightarrow{Pt/Rh, 800^circ C} 4NO + 6H_2O$ (Ostwald first step).

Uses — Fertilizers, nitric acid, refrigerants.

3. Oxides of Nitrogen (NOx)

$N_2O$ (Nitrous oxide) — +1, colorless, neutral, diamagnetic, 'laughing gas'. Prep: $NH_4NO_3 xrightarrow{\text{heat}} N_2O + 2H_2O$.
$NO$ (Nitric oxide) — +2, colorless, neutral, paramagnetic (odd electron). Prep: $3Cu + 8HNO_3(\text{dilute}) \rightarrow 3Cu(NO_3)_2 + 2NO + 4H_2O$. Oxidizes in air: $2NO + O_2 \rightarrow 2NO_2$ (reddish-brown).
$N_2O_3$ (Dinitrogen trioxide) — +3, blue solid, acidic (anhydride of $HNO_2$). Prep: $NO + NO_2 xrightarrow{250,\text{K}} N_2O_3$.
$NO_2$ (Nitrogen dioxide) — +4, reddish-brown gas, acidic, paramagnetic. Prep: $Cu + 4HNO_3(\text{conc.}) \rightarrow Cu(NO_3)_2 + 2NO_2 + 2H_2O$. Dimerizes: $2NO_2 \rightleftharpoons N_2O_4$ (brown $ightleftharpoons$ colorless).
$N_2O_4$ (Dinitrogen tetroxide) — +4, colorless solid/liquid, diamagnetic, dimer of $NO_2$.
$N_2O_5$ (Dinitrogen pentoxide) — +5, colorless solid, acidic (anhydride of $HNO_3$), strong oxidizing agent. Prep: $2HNO_3 + P_4O_{10} \rightarrow N_2O_5 + 2HPO_3$.

4. Nitric Acid ($HNO_3$)

Lab Prep — $KNO_3 + H_2SO_4(\text{conc.}) xrightarrow{\text{heat}} KHSO_4 + HNO_3$.
Industrial Prep (Ostwald Process)

1. $4NH_3(g) + 5O_2(g) xrightarrow{Pt/Rh,gauze, 800^circ C} 4NO(g) + 6H_2O(g)$ 2. $2NO(g) + O_2(g) \rightarrow 2NO_2(g)$ 3. $3NO_2(g) + H_2O(l) \rightarrow 2HNO_3(aq) + NO(g)$ (NO recycled)

Properties — Colorless fuming liquid (yellowish if $NO_2$ dissolved), strong acid, powerful oxidizing agent.

* Reactions with Metals: * **Dilute $HNO_3$**: Generally forms $NO$. E.g., $3Cu + 8HNO_3(\text{dilute}) \rightarrow 3Cu(NO_3)_2 + 2NO + 4H_2O$. * **Concentrated $HNO_3$**: Generally forms $NO_2$.

E.g., $Cu + 4HNO_3(\text{conc.}) \rightarrow Cu(NO_3)_2 + 2NO_2 + 2H_2O$. * **Very dilute $HNO_3$**: Can form $N_2O$ or $NH_4NO_3$ (e.g., with Zn). * Passivity: Fe, Cr, Al become passive due to protective oxide layer with conc.

$HNO_3$. * Reactions with Non-metals: Oxidizes C, S, P to their highest oxyacids. E.g., $C + 4HNO_3(\text{conc.}) \rightarrow CO_2 + 4NO_2 + 2H_2O$.

Uses — Fertilizers, explosives, pickling of stainless steel.

Vyyuha Quick Recall

For the Oxides of Nitrogen and their oxidation states, remember: Never Never Never Never Never Never Outside Outside Outside Outside Outside

This represents the number of Nitrogen and Oxygen atoms in the common oxides, and helps recall their oxidation states in increasing order:

$N_2O$ (N=+1) - Never Outside (1 N, 1 O for oxidation state calc) $NO$ (N=+2) - Never Outside (1 N, 1 O for oxidation state calc) $N_2O_3$ (N=+3) - Never Outside (2 N, 3 O for oxidation state calc) $NO_2$ (N=+4) - Never Outside (1 N, 2 O for oxidation state calc) $N_2O_4$ (N=+4) - Never Outside (2 N, 4 O for oxidation state calc) $N_2O_5$ (N=+5) - Never Outside (2 N, 5 O for oxidation state calc)

While the mnemonic itself is simple, the key is to associate the increasing number of 'O's (and 'N's for $N_2O_x$) with the increasing oxidation state of nitrogen. For example, $N_2O$ is +1, $NO$ is +2, $N_2O_3$ is +3, $NO_2$ is +4, $N_2O_4$ is +4, $N_2O_5$ is +5. It's a quick way to mentally check the order and corresponding oxidation states.