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| salt (chemical) | |
|---|---|
| Name | Sodium chloride |
| Formula | NaCl |
| Molar mass | 58.44 g·mol−1 |
| Appearance | White crystalline solid |
| Melting point | 801 °C |
| Boiling point | 1413 °C |
| Density | 2.165 g·cm−3 |
| Solubility | 35.9 g/100 mL (20 °C) |
salt (chemical) is a class of ionic compounds formed by the neutralization reaction between acids and bases, typified by sodium chloride. Salts comprise cations and anions arranged in crystalline lattices, exhibit characteristic properties such as high melting points and electrical conductivity in molten or aqueous states, and play central roles in chemical industries, geologic systems, physiology, and culture.
A chemical salt is defined in inorganic chemistry as an ionic compound composed of positively charged cations and negatively charged anions derived from a base and an acid, respectively, as taught in texts used at Massachusetts Institute of Technology, University of Cambridge, California Institute of Technology, University of Oxford, and ETH Zurich. Typical properties include crystalline habit as seen in samples described by André-Jean Fremy and catalogued in datasets from International Union of Pure and Applied Chemistry, high lattice enthalpy studied at Max Planck Institute for Solid State Research, and distinct solubility behavior exemplified in reports by U.S. Geological Survey, National Institutes of Health, and World Health Organization. Salts conduct electricity when molten or dissolved, a characteristic measured by techniques developed at Bell Laboratories and applied in instruments from Agilent Technologies and Shimadzu Corporation. Physical constants such as lattice parameters and defect chemistry are reported in compilations like those from Royal Society of Chemistry and are central to research at Argonne National Laboratory and Lawrence Berkeley National Laboratory.
Salts form via neutralization reactions illustrated in pedagogical resources at Harvard University and in classical experiments attributed to early chemists working in cities like Paris and London. Classification schemes distinguish simple binary salts (e.g., halides), oxyanionic salts (e.g., sulfates, nitrates, carbonates), double salts, coordination salts, and complex salts—categories used in curricula at University of Tokyo and Peking University. Mineralogical classification of salt minerals such as halite and gypsum appears in references from Smithsonian Institution and Natural History Museum, London, while synthetic inorganic salts are studied in laboratories at Bell Labs, Los Alamos National Laboratory, and Scripps Research. The Brønsted–Lowry and Lewis frameworks from work associated with Johannes Nicolaus Brønsted and Gilbert N. Lewis underpin theoretical descriptions of salt formation, which are elaborated in treatises published by American Chemical Society.
Salts occur in evaporite deposits like those mapped by United States Geological Survey and in marine brines sampled by research vessels from Woods Hole Oceanographic Institution and Scripps Institution of Oceanography. Major natural sources include seawater with composition characterized by expeditions led from Challenger (1872–1876) and later studies by James Cook-era voyages, continental salt domes studied near Gulf of Mexico and Permian Basin, and subterranean halite beds exploited in regions such as Sichuan, Punjab, Abra Pampa, and Salar de Uyuni. Industrial deposits and salt mines like those at Wieliczka Salt Mine, Khewra Salt Mine, Sifto Salt Mine, and Salt Range have been documented by national geological surveys. Atmospheric and extraterrestrial salts have been reported in analyses by NASA missions including Mars Reconnaissance Orbiter and Cassini–Huygens.
Salts have diverse applications across sectors represented by organizations such as DuPont, BASF, Dow Chemical Company, and GlaxoSmithKline. Sodium chloride is fundamental in food preservation practices traced to techniques employed in Han Dynasty China and medieval Europe, and in modern food processing regulated by agencies like European Food Safety Authority and Food and Drug Administration. Industrial uses include chlorine and sodium production via electrolytic processes commercialized by firms like Koch Industries and used in polyvinyl chloride manufacture referenced in standards from International Electrotechnical Commission. Salts serve roles in deicing roads administered by municipal bodies in cities such as New York City and London, in water softening systems deployed in facilities run by Veolia and SUEZ, and as reagents in pharmaceuticals developed at Pfizer and Roche. Specialized salts are essential in batteries researched at Toyota Research Institute, in catalysts studied at Max Planck Society, and in optical and electronic materials produced by Intel and Samsung Electronics.
Physiological importance of electrolyte salts (sodium, potassium, chloride) is central to research at National Institutes of Health and in clinical guidelines from American Heart Association and World Health Organization. Imbalances contribute to conditions investigated in cohorts at Mayo Clinic, Cleveland Clinic, and academic hospitals affiliated with Johns Hopkins University School of Medicine. Ecological impacts of road salt on freshwater systems have been documented by researchers at Cornell University, University of Minnesota, and environmental agencies such as Environmental Protection Agency. Soil salinization affecting agriculture in regions managed by Food and Agriculture Organization and studies by International Rice Research Institute and CIMMYT links to policy discussions at United Nations. Toxicological profiles and exposure limits are set by bodies like Occupational Safety and Health Administration and European Chemicals Agency.
Commercial salt production methods—solar evaporation, solution mining, and rock salt mining—are implemented by companies including Cargill, Morton Salt, K+S AG, and state enterprises in China National Salt Industry Corporation. Evaporative solar pans practiced in regions like San Francisco Bay salt ponds and Maras, Peru draw on climatology datasets from National Oceanic and Atmospheric Administration. Vacuum evaporation and electrolysis for chlorine and caustic soda derive from processes developed historically at Chloralkali plants and standardized by industrial codices from American Society of Mechanical Engineers. Quality control, crystallization engineering, and environmental management are overseen using protocols from ISO and consultancy by McKinsey & Company.
Salt has shaped economies and geopolitics from antiquity—linked to trade routes such as the Salt Road, revenues like the Salt tax (gabelle) in France, and conflicts around resources documented in histories of Rome and Mali Empire. Cultural practices involving salt appear in rituals of Shinto, customs recorded in Torah and Bible, and literary references from Homer to William Shakespeare. Monetary and ceremonial uses influenced institutions such as Venice and the Ottoman Empire, while archaeological finds in sites like Pompeii and Çatalhöyük illustrate continuity. Modern commemorations include museums at Salts Mill and heritage listings like Wieliczka Salt Mine.
Category:Inorganic compounds