Nitrogen and phosphorus are essential for life, while carbon and silicon are important elements at the boundary between inorganic and organic chemistry. Each forms compounds with various oxidation numbers.
Basic Knowledge
Nitrogen N2: 78% of the atmosphere, with a very stable N≡N triple bond. Industrial fixation is carried out by the Haber-Bosch process N2 + 3H2 ⇄ 2NH3 (Fe catalyst, 400-600℃, 200-1000 atm). Ammonia NH3 is a Bronsted base and is collected by upward displacement of air. Industrial production of nitric acid HNO3 uses the Ostwald process: NH3 → NO → NO2 → HNO3 (platinum catalyst). Dilute nitric acid dissolves Cu and Ag oxidatively, producing NO, while concentrated nitric acid produces NO2. Fe, Al, and Ni become passive.
Phosphorus P: Its allotropes include white phosphorus (P4, spontaneously ignites, highly poisonous, stored under water) and red phosphorus (nonpoisonous, used on the striking surface of matches). Tetraphosphorus decoxideP4O10 is a powerful drying and dehydrating agent.
Carbon C: Has many allotropes (diamond, graphite, fullerene, carbon nanotubes, and graphene). Silicon Si: The second most abundant element in the Earth's crust; it exists as SiO2 (quartz and rock crystal) and silicate minerals. It is a key material in the semiconductor industry.
Haber-Bosch process (NH3 synthesis, Fe catalyst, supports global food production)
Ostwald process (HNO3 synthesis, platinum catalyst)
Passivation (a dense oxide film forms on Fe, Al, and Ni in concentrated nitric acid, preventing them from dissolving)
Aqua regia (concentrated HCl:concentrated HNO3=3:1, dissolves Au and Pt)
P4O10 (powerful dehydrating agent, acid anhydride of phosphoric acid)
SiO2 (covalent-network crystal, glass, quartz, and semiconductor substrates)
Further Study (Principles and Applications)
The Haber-Bosch process is one of the greatest inventions of the 20th century. By converting atmospheric nitrogen into fertilizer, it multiplied global food production and supports the modern population of 8 billion people. At the same time, eutrophication and groundwater pollution caused by nitrogen oxides have occurred, and humanity has greatly altered the nitrogen cycle.
Aqua regia is the only reagent that dissolves Au: Au + 4HCl + HNO3 → HAuCl4 + NO + 2H2O. HNO3 oxidizes Au, while Cl- forms the complex [AuCl4]-, driving the dissolution equilibrium forward.
Silicon is a foundation material of modern industry, used in glass (SiO2+Na2CO3+CaCO3), ceramics, silicate minerals, water glass (Na2SiO3), silica gel (drying agent), silicone resin, and semiconductor-grade Si (ultra-high purity exceeding 99.9999999%).
- Haber-Bosch process: N2+3H2→2NH3, Fe catalyst, high temperature and pressure
- Ostwald process: HNO3 is produced from NH3 in three stages
- Dilute nitric acid → NO; concentrated nitric acid → NO2
- Fe, Al, and Ni become passive in concentrated nitric acid
- Aqua regia (HCl:HNO3=3:1) dissolves Au and Pt
- White phosphorus spontaneously ignites and is highly poisonous; red phosphorus is safer
- SiO2 is a covalent-network crystal with a high melting point and dissolves in HF
Points to Note (Common Confusions and Frequent Mistakes)
① Dilute nitric acid produces NO, while concentrated nitric acid produces NO2 (remember their colors: NO is colorless and NO2 is reddish brown). ② Passivation applies to Fe, Al, and Ni. ③ NH3 is collected by upward displacement of air (it is lighter than air and highly soluble in water). ④ White phosphorus and red phosphorus are allotropes with completely different properties and storage methods (white phosphorus is stored under water).
Practice
- Write the reaction equations and catalysts for the Haber-Bosch process and the Ostwald process.
- Write the reaction equation for concentrated nitric acid dissolving copper (pay attention to the gas produced).
- Explain how aqua regia dissolves Au from both the viewpoints of oxidation and complex formation.