Chlorine is a chemical element; it has symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is a yellow-green gas at room temperature. It is an extremely reactive element and a strong oxidising agent: among the elements, it has the highest electron affinity and the third-highest electronegativity on the revised Pauling scale, behind only oxygen and fluorine.
The halogens are a group in the periodic table consisting of six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and the radioactive elements astatine (At) and tennessine (Ts), though some authors would exclude tennessine as its chemistry is unknown and is theoretically expected to be more like that of gallium. In the modern IUPAC nomenclature, this group is known as group 17.
Sodium is a chemical element; it has symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable isotope is 23Na. The free metal does not occur in nature and must be prepared from compounds. Sodium is the sixth most abundant element in the Earth's crust and exists in numerous minerals such as feldspars, sodalite, and halite (NaCl). Many salts of sodium are highly water-soluble: sodium ions have been leached by the action of water from the Earth's minerals over eons, and thus sodium and chlorine are the most common dissolved elements by weight in the oceans.
Salinity is the saltiness or amount of salt dissolved in a body of water, called saline water. It is usually measured in g/L or g/kg.
Brine is water with a high-concentration solution of salt. In diverse contexts, brine may refer to the salt solutions ranging from about 3.5% up to about 26%. Brine forms naturally due to evaporation of ground saline water but it is also generated in the mining of sodium chloride. Brine is used for food processing and cooking, for de-icing of roads and other structures, and in a number of technological processes. It is also a by-product of many industrial processes, such as desalination, so it requires wastewater treatment for proper disposal or further utilization.
Sodium chloride, commonly known as edible salt, is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chlorine ions. In its edible form, it is commonly used as a condiment and food preservative. Large quantities of sodium chloride are used in many industrial processes, and it is a major source of sodium and chlorine compounds used as feedstocks for further chemical syntheses. Another major application of sodium chloride is deicing of roadways in sub-freezing weather.
Potassium chloride is a metal halide salt composed of potassium and chlorine. It is odorless and has a white or colorless vitreous crystal appearance. The solid dissolves readily in water, and its solutions have a salt-like taste. Potassium chloride can be obtained from ancient dried lake deposits. KCl is used as a fertilizer, in medicine, in scientific applications, domestic water softeners, and in food processing, where it may be known as E number additive E508.
Seawater, or sea water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5%. This means that every kilogram of seawater has approximately 35 grams (1.2 oz) of dissolved salts. The average density at the surface is 1.025 kg/L. Seawater is denser than both fresh water and pure water because the dissolved salts increase the mass by a larger proportion than the volume. The freezing point of seawater decreases as salt concentration increases. At typical salinity, it freezes at about −2 °C (28 °F). The coldest seawater still in the liquid state ever recorded was found in 2010, in a stream under an Antarctic glacier: the measured temperature was −2.6 °C (27.3 °F).
The self-ionization of water (also autoionization of water, and autodissociation of water, or simply dissociation of water) is an ionization reaction in pure water or in an aqueous solution, in which a water molecule, H2O, deprotonates (loses the nucleus of one of its hydrogen atoms) to become a hydroxide ion, OH−. The hydrogen nucleus, H+, immediately protonates another water molecule to form a hydronium cation, H3O+. It is an example of autoprotolysis, and exemplifies the amphoteric nature of water.
Magnesium chloride is an inorganic compound with the formula MgCl2. It forms hydrates MgCl2·nH2O, where n can range from 1 to 12. These salts are colorless or white solids that are highly soluble in water. These compounds and their solutions, both of which occur in nature, have a variety of practical uses. Anhydrous magnesium chloride is the principal precursor to magnesium metal, which is produced on a large scale. Hydrated magnesium chloride is the form most readily available.
The chloralkali process is an industrial process for the electrolysis of sodium chloride (NaCl) solutions. It is the technology used to produce chlorine and sodium hydroxide, which are commodity chemicals required by industry. Thirty five million tons of chlorine were prepared by this process in 1987. The chlorine and sodium hydroxide produced in this process are widely used in the chemical industry.
Electrolysis of water is using electricity to split water into oxygen and hydrogen gas by electrolysis. Hydrogen gas released in this way can be used as hydrogen fuel, but must be kept apart from the oxygen as the mixture would be extremely explosive. Separately pressurised into convenient 'tanks' or 'gas bottles', hydrogen can be used for oxyhydrogen welding and other applications, as the hydrogen / oxygen flame can reach approximately 2,800°C.
Salt water chlorination is a process that uses dissolved salt for the chlorination of swimming pools and hot tubs. The chlorine generator uses electrolysis in the presence of dissolved salt to produce chlorine gas or its dissolved forms, hypochlorous acid and sodium hypochlorite, which are already commonly used as sanitizing agents in pools. Hydrogen is produced as byproduct too.
Total dissolved solids (TDS) is a measure of the dissolved combined content of all inorganic and organic substances present in a liquid in molecular, ionized, or micro-granular suspended form. TDS are often measured in parts per million (ppm). TDS in water can be measured using a digital meter.
Molten salt is salt which is solid at standard temperature and pressure but liquified due to elevated temperature. A salt that is liquid even at standard temperature and pressure is usually called a room-temperature ionic liquid, and molten salts are technically a class of ionic liquids.
Reverse osmosis (RO) is a water purification process that uses a semi-permeable membrane to separate water molecules from other substances. RO applies pressure to overcome osmotic pressure that favors even distributions. RO can remove dissolved or suspended chemical species as well as biological substances, and is used in industrial processes and the production of potable water. RO retains the solute on the pressurized side of the membrane and the purified solvent passes to the other side. It relies on the relative sizes of the various molecules to decide what passes through. "Selective" membranes reject large molecules, while accepting smaller molecules.
Frost flowers are ice crystals commonly found growing on young sea ice and thin lake ice in cold, calm conditions. The ice crystals are similar to hoar frost, and are commonly seen to grow in patches around 3–4 cm in diameter. Frost flowers growing on sea ice have extremely high salinities and concentrations of other sea water chemicals and, because of their high surface area, are efficient releasers of these chemicals into the atmosphere.
Brine mining is the extraction of useful materials which are naturally dissolved in brine. The brine may be seawater, other surface water, groundwater, or hyper-saline solutions from several industries. It differs from solution mining or in-situ leaching in that those methods inject water or chemicals to dissolve materials which are in a solid state; in brine mining, the materials are already dissolved.
Salt poisoning is an intoxication resulting from the excessive intake of sodium in either solid form or in solution. Salt poisoning sufficient to produce severe symptoms is rare, and lethal salt poisoning is possible but even rarer. The lethal dose of table salt is roughly 0.5–1g per kg of body weight.
Crop tolerance to seawater is the ability of an agricultural crop to withstand the high salinity induced by irrigation with seawater, or a mixture of fresh water and seawater. There are crops that can grow on seawater and demonstration farms have shown the feasibility. The government of the Netherlands reports a breakthrough in food security as specific varieties of potatoes, carrots, red onions, white cabbage and broccoli appear to thrive if they are irrigated with salt water.
