Nitrogen Chemistry

Cheatsheet Content

### Nitrogen (N₂) Properties - **Atomic Number:** 7 - **Atomic Mass:** 14.007 u - **Electron Configuration:** $[He] 2s^2 2p^3$ - **Common Oxidation States:** -3, 0, +1, +2, +3, +4, +5 - **Bonding:** Triple bond in N₂ (very stable, inert) - **State at Room Temp:** Gas ### Ammonia (NH₃) & Ammonium (NH₄⁺) - **Structure:** Trigonal pyramidal ($sp^3$ hybridization, lone pair on N) for NH₃, Tetrahedral ($sp^3$ hybridization) for NH₄⁺. - **Properties:** Pungent, colorless gas. Highly soluble in water due to hydrogen bonding. Forms alkaline solutions. - **Preparation:** - **Haber-Bosch Process:** $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$ (Industrial synthesis, high pressure/temperature, Fe catalyst. Links **elemental nitrogen** to **ammonia**). - **Hydrolysis of Nitrides:** $Mg_3N_2(s) + 6H_2O(l) \rightarrow 3Mg(OH)_2(s) + 2NH_3(g)$ (General method for nitrides of active metals). - **Lab preparation (from ammonium salts):** $NH_4Cl(s) + NaOH(aq) \xrightarrow{\Delta} NH_3(g) + NaCl(aq) + H_2O(l)$ (Heating an ammonium salt with a strong base). - **Reactions:** - **Weak Base:** $NH_3(aq) + H_2O(l) \rightleftharpoons NH_4^+(aq) + OH^-(aq)$ ($K_b = 1.8 \times 10^{-5}$). Forms **ammonium ion**. - **Combustion:** $4NH_3(g) + 3O_2(g) \rightarrow 2N_2(g) + 6H_2O(g)$ (In excess ammonia, forms **elemental nitrogen**). - **Catalytic Oxidation (Ostwald Process start):** $4NH_3(g) + 5O_2(g) \xrightarrow{Pt/Rh, 800^\circ C} 4NO(g) + 6H_2O(g)$ (Key industrial step for producing **Nitric Oxide**, a precursor to **Nitric Acid**). - **Formation of Amides:** $2Na(s) + 2NH_3(l) \rightarrow 2NaNH_2(s) + H_2(g)$ (Ammonia acting as a very weak acid in liquid ammonia solvent). - **Complexation:** $Cu^{2+}(aq) + 4NH_3(aq) \rightarrow [Cu(NH_3)_4]^{2+}(aq)$ (Forms deeply colored transition metal complexes, e.g., tetraamminecopper(II) ion). - **Reaction with Acids:** $NH_3(g) + HCl(g) \rightarrow NH_4Cl(s)$ (Forms **ammonium salts**). - **Uses:** Fertilizers (urea, ammonium nitrate), refrigerants, cleaning agents, synthesis of other nitrogen compounds. ### Nitrogen Oxides #### 1. Nitrous Oxide (N₂O) - Laughing Gas - **Oxidation State of N:** +1 - **Preparation:** $NH_4NO_3(s) \xrightarrow{\Delta} N_2O(g) + 2H_2O(g)$ (from **Ammonium Nitrate**, a salt related to **Ammonia** and **Nitric Acid**) - **Properties:** Colorless gas, anesthetic, supports combustion (similar to O₂) #### 2. Nitric Oxide (NO) - **Oxidation State of N:** +2 - **Preparation:** - **Catalytic Oxidation of NH₃:** $4NH_3(g) + 5O_2(g) \xrightarrow{Pt/Rh} 4NO(g) + 6H_2O(g)$ (key step in Ostwald Process, starting from **Ammonia**) - **Lab (Cu + HNO₃):** $3Cu(s) + 8HNO_3(dilute) \rightarrow 3Cu(NO_3)_2(aq) + 2NO(g) + 4H_2O(l)$ (reduction of **Nitric Acid**) - **Properties:** Colorless gas, paramagnetic (odd number of electrons), reacts with O₂ - **Reaction with O₂:** $2NO(g) + O_2(g) \rightarrow 2NO_2(g)$ (forms **Nitrogen Dioxide**) #### 3. Nitrogen Dioxide (NO₂) - **Oxidation State of N:** +4 - **Preparation:** - **Reaction of NO with O₂:** $2NO(g) + O_2(g) \rightarrow 2NO_2(g)$ (from **Nitric Oxide**) - **Lab (Cu + HNO₃ conc.):** $Cu(s) + 4HNO_3(conc.) \rightarrow Cu(NO_3)_2(aq) + 2NO_2(g) + 2H_2O(l)$ (stronger reduction of **Nitric Acid**) - **Properties:** Brown gas, toxic, readily dimerizes - **Dimerization:** $2NO_2(g) \rightleftharpoons N_2O_4(g)$ (colorless, dinitrogen tetroxide) - **Reaction with Water:** $3NO_2(g) + H_2O(l) \rightarrow 2HNO_3(aq) + NO(g)$ (forms **Nitric Acid** and regenerates **Nitric Oxide**, contributing to acid rain) #### 4. Dinitrogen Pentoxide (N₂O₅) - **Oxidation State of N:** +5 - **Preparation:** $2HNO_3(l) + P_4O_{10}(s) \rightarrow N_2O_5(s) + 4HPO_3(l)$ (dehydration of **Nitric Acid**) - **Properties:** White solid, strong oxidizing agent, anhydride of nitric acid - **Reaction with Water:** $N_2O_5(s) + H_2O(l) \rightarrow 2HNO_3(aq)$ (reforms **Nitric Acid**) ### Oxoacids of Nitrogen #### 1. Nitrous Acid (HNO₂) - **Oxidation State of N:** +3 - **Preparation:** $NaNO_2(aq) + HCl(aq) \rightarrow HNO_2(aq) + NaCl(aq)$ (unstable, prepared in situ) - **Properties:** Weak acid, disproportionates upon heating - **Disproportionation:** $3HNO_2(aq) \rightarrow HNO_3(aq) + 2NO(g) + H_2O(l)$ #### 2. Nitric Acid (HNO₃) - **Oxidation State of N:** +5 - **Preparation (Ostwald Process):** 1. $4NH_3(g) + 5O_2(g) \xrightarrow{Pt/Rh} 4NO(g) + 6H_2O(g)$ 2. $2NO(g) + O_2(g) \rightarrow 2NO_2(g)$ 3. $3NO_2(g) + H_2O(l) \rightarrow 2HNO_3(aq) + NO(g)$ - **Properties:** Strong acid, strong oxidizing agent - **Reactions with Metals:** - **Dilute HNO₃:** $3Cu(s) + 8HNO_3(dilute) \rightarrow 3Cu(NO_3)_2(aq) + 2NO(g) + 4H_2O(l)$ - **Concentrated HNO₃:** $Cu(s) + 4HNO_3(conc.) \rightarrow Cu(NO_3)_2(aq) + 2NO_2(g) + 2H_2O(l)$ - **Very Dilute HNO₃ (active metals like Zn, Mg):** $4Zn(s) + 10HNO_3(v.dilute) \rightarrow 4Zn(NO_3)_2(aq) + NH_4NO_3(aq) + 3H_2O(l)$ - **Passivity:** Reacts with Fe, Cr, Al to form a protective oxide layer, preventing further reaction. ### Other Nitrogen Compounds #### 1. Nitrogen Trichloride (NCl₃) - **Oxidation State of N:** -3 - **Preparation:** $NH_3(g) + 3Cl_2(g) \rightarrow NCl_3(l) + 3HCl(g)$ (explosive, often formed as byproduct) - **Properties:** Yellow, oily, highly explosive liquid. #### 2. Hydrazine (N₂H₄) - **Oxidation State of N:** -2 - **Preparation:** $2NH_3(aq) + NaOCl(aq) \rightarrow N_2H_4(aq) + NaCl(aq) + H_2O(l)$ (Raschig Process) - **Properties:** Colorless liquid, strong reducing agent, rocket fuel. #### 3. Hydroxylamine (NH₂OH) - **Oxidation State of N:** -1 - **Preparation:** Reduction of nitrites or nitric oxide. - **Properties:** White crystalline solid, reducing agent. #### 4. Azides (e.g., NaN₃) - **Oxidation State of N:** -1/3 (average) - **Structure:** Linear $N_3^-$ ion ($[\stackrel{\cdot\cdot}{N}=\stackrel{+}{N}=\stackrel{\cdot\cdot}{N}]^- \leftrightarrow [\stackrel{\cdot\cdot}{N}-\stackrel{+}{N}\equiv N]$) - **Properties:** Explosive (e.g., lead azide, sodium azide in airbags). - **Decomposition of Sodium Azide:** $2NaN_3(s) \xrightarrow{\Delta} 2Na(s) + 3N_2(g)$