The industrial and applied chemistry aspects of Groups 16-18 are essential for NEET conceptual questions.
Contact Process — Industrial H2SO4 Manufacture: The Contact process is the cornerstone industrial application in this chapter. The key equilibrium step is 2SO2 + O2 ⇌ 2SO3 at 450°C with V2O5 catalyst. This temperature represents the kinetic-thermodynamic compromise: the exothermic reaction thermodynamically favors low temperature for better yield, but the catalyst requires ~400°C to be active. The absorption of SO3 in concentrated H2SO4 (not water) to form oleum (H2S2O7) is the critical industrial innovation that solved the acid mist problem. H2SO4 from the Contact process is used in: fertilizer manufacture (superphosphate, ammonium sulfate), petroleum refining, metallurgy, detergent synthesis, explosive manufacture, and as a laboratory reagent.
Bleaching Powder Applications: CaOCl2 (calcium oxychloride) is manufactured by passing Cl2 over slaked lime at approximately 40°C. It serves as: a textile bleaching agent (cotton, linen), a paper pulp bleaching agent, a water disinfectant and purifier, a disinfectant in hospitals and swimming pools, and a stain remover. The active bleaching species is the hypochlorite ion (O) and nascent oxygen released from it.
Hydrofluoric Acid (HF) Special Properties: HF is unique among hydrogen halides in its ability to etch glass via: 4HF + SiO2 → SiF4↑ + 2H2O. This makes HF extremely dangerous as it dissolves glass lab equipment. It must be stored in PTFE (polytetrafluoroethylene) plastic or lead containers. HF is used industrially in glass frosting, semiconductor manufacturing (etching silicon chips), and uranium hexafluoride production (nuclear fuel processing).
Ozone Applications: Ozone's powerful oxidizing action (via nascent oxygen release) is exploited in: water purification (stronger disinfectant than Cl2, no taste/odor issues), industrial bleaching, and air purification. The stratospheric ozone layer (15-35 km altitude) absorbs UV-B and UV-C radiation (200-315 nm), protecting life from DNA damage and skin cancer.
Xenon in Technology: Xenon's noble gas properties (stable, non-toxic, high atomic mass) make it valuable in: high-intensity discharge lamps (HID headlamps, cinema projectors), xenon ion thrusters for spacecraft propulsion, medical imaging (CT scan contrast agents), and as a general anesthetic (expensive but medically effective).
Noble Gas Clathrates: Physical cage compounds where noble gases are trapped without bonding are used in: food preservation (Ar, Kr), geological dating (He, Ar trapping in rocks to determine age), and drug delivery research (Xe clathrate hydrates as oxygen carriers).