Common Compounds

Chemical compounds are broadly classified into inorganic and organic categories based on their composition and origin.

Inorganic Compounds

Inorganic compounds typically lack carbon-hydrogen bonds and are derived from non-living sources such as minerals and crustal deposits. They include acids, bases, salts, and oxides that form the backbone of the chemical and manufacturing industries.

Organic Compounds

Organic compounds primarily consist of carbon atoms bonded to hydrogen, oxygen, nitrogen, and other non-metals. Historically associated with living organisms, they encompass a vast array of substances including hydrocarbons, alcohols, and polymers used in daily life.

Essential Salts and Daily-Use Compounds

Salts are ionic compounds produced by the neutralization reaction of an acid and a base. They play critical roles in human physiology, agriculture, and industrial processes.

Sodium-Based Compounds

Sodium forms some of the most widely used compounds in households and industries.

• Sodium Chloride (Common Salt / Halite): Represented as NaCl. It is essential for human biological functions, acting as an electrolyte and aiding nerve impulse transmission. Industrially, it serves as a raw material for manufacturing chlorine and sodium hydroxide.
• Sodium Bicarbonate (Baking Soda): Represented as NaHCO₃. It acts as a leavening agent in baking by releasing carbon dioxide gas when heated. It is also used as a mild antiseptic and in antacids to neutralize stomach acidity.
• Sodium Carbonate (Washing Soda): Represented as Na₂CO₃ · 10H₂O in its decahydrate form. It is utilized in the manufacture of glass, soap, and paper, and acts as a water softener to remove permanent hardness.
• Sodium Hydroxide (Caustic Soda): Represented as NaOH. A strong base used extensively in paper pulp manufacturing, petroleum refining, and soap making.

Calcium-Based Compounds

Calcium compounds are vital structural materials in nature and engineering.

• Calcium Carbonate (Limestone / Marble / Chalk): Represented as CaCO₃. It is the primary component of sedimentary rocks, shells of marine organisms, and antacid tablets. It serves as a fundamental raw material in the cement industry.
• Calcium Oxide (Quicklime): Represented as CaO. Produced by the thermal decomposition of limestone. It is used in steel manufacturing, water treatment, and as a drying agent.
• Calcium Hydroxide (Slaked Lime): Represented as Ca(OH)₂. Formed by reacting quicklime with water. It is used in whitewashing walls, sewage treatment, and soil treatment to neutralize acidity.
• Calcium Hypochlorite (Bleaching Powder): Represented as CaOCl₂. It is utilized as a disinfecting agent for drinking water and as a bleaching agent in textile and paper industries.
• Plaster of Paris and Gypsum: Gypsum is CaSO₄ · 2H₂O. When heated to 373 Kelvin, it loses water molecules to form Plaster of Paris (CaSO₄ · 1/2H₂O). It is used for casting statues, setting fractured bones, and fireproofing structures.

Industrial and Agricultural Chemicals

Chemical compounds drive agricultural productivity and heavy industrial synthesis, serving as fertilizers, refrigerants, and manufacturing precursors.

Nitrogen and Phosphorus Precursors

These compounds are critical for global food security through fertilizer production.

• Ammonia: Represented as NH₃. Synthesized through the Haber-Bosch process. It is the primary precursor for nitrogenous fertilizers like urea and ammonium nitrate.
• Urea: Represented as NH₂CONH₂. It is the most widely used nitrogenous fertilizer due to its high nitrogen content. It is also used in the manufacture of plastics and adhesives.
• Phosphoric Acid: Represented as H₃PO₄. Used chiefly in the production of triple superphosphate fertilizers and as a rust converter.

Industrial Acids and Gases

Acids form the core of chemical processing, often serving as indicators of a nation’s industrial output.

• Sulfuric Acid (Oil of Vitriol): Represented as H₂SO₄. Often referred to as the “King of Chemicals” due to its extensive use in car batteries, fertilizer manufacturing, mineral processing, and chemical synthesis.
• Hydrochloric Acid (Muriatic Acid): Represented as HCl. Secreted naturally in the human stomach to aid digestion. Industrially used for pickled steel, leather processing, and gelatin production.
• Nitric Acid (Aqua Fortis): Represented as HNO₃. Highly corrosive acid used in making explosives like TNT, nitroglycerin, and in the production of ammonium nitrate fertilizers.
• Nitrous Oxide (Laughing Gas): Represented as N₂O. Used as an anesthetic and analgesic in dentistry and surgery, and as an oxidizer in rocketry.

Organic and Household Carbon Compounds

Organic carbon compounds dominate domestic applications, pharmaceuticals, and fuel systems.

Alcohols and Acids

Short-chain organic molecules find widespread utility as solvents and preservatives.

• Methanol (Wood Alcohol): Represented as CH₃OH. Highly toxic alcohol that causes blindness if ingested. Used as an industrial solvent, antifreeze, and denaturant for ethanol.
• Ethanol (Grain Alcohol): Represented as C₂H₅OH. The active ingredient in alcoholic beverages, widely used as a solvent in medicines, perfumes, and increasingly as a biofuel blended with petrol.
• Acetic Acid (Ethanoic Acid): Represented as CH₃COOH. A 5-8% solution of acetic acid in water is known as vinegar, used extensively as a food preservative and flavoring agent.
• Chloroform (Trichloromethane): Represented as CHCl₃. Historically used as a general anesthetic, it is now primarily used as an industrial solvent and in the production of refrigerants.

Hydrocarbons and Domestic Fuels

Hydrocarbons serve as the primary sources of energy in modern civilization.

• Methane (Marsh Gas): Represented as CH₄. The simplest alkane and primary constituent of Natural Gas, Compressed Natural Gas (CNG), and Biogas. It is a potent greenhouse gas emitted from wetlands and paddy fields.
• Propane and Butane: Represented as C₃H₈ and C₄H₁₀ respectively. These liquefied gases are the major components of Liquefied Petroleum Gas (LPG) used for domestic cooking. Ethyl mercaptan (C₂H₅SH) is added to LPG to give it a distinct odor for leak detection.

Important Chemical Trivia for Prelims

Specific chemical compounds possess distinct properties or historical significance that frequently appear in competitive examinations.

Mixed Chemical Formulations

• Aqua Regia: A highly corrosive, fuming mixture formed by combining concentrated Hydrochloric Acid (HCl) and concentrated Nitric Acid (HNO₃) in a 3:1 ratio by volume. It is one of the few reagents capable of dissolving noble metals like gold and platinum.
• Dry Ice: Solidified carbon dioxide (CO₂). It undergoes sublimation, transitioning directly from a solid to a gas at atmospheric pressure. Used extensively as a cooling agent for preserving food and biological samples.
• Alum (Potash Alum): Represented as K₂SO₄ · Al₂(SO₄)₃ · 24H₂O. It is used in water purification processes through coagulation, where it helps settle suspended impurities.
• Heavy Water: Deuterium oxide (D₂O). A form of water containing the hydrogen isotope deuterium. It is used as a neutron moderator and coolant in nuclear reactors, such as Pressurized Heavy Water Reactors (PHWRs).
• Tear Gas (CS Gas): Chemically known as 2-chlorobenzalmalononitrile (C₁₀H₅ClN₂). It is used as a riot control agent due to its incapacitating effects on the eyes and respiratory system.