a b "Bleaching". Encyclopædia Britannica (9th Edition (1875) and 10th Edition (1902)ed.). Archived from the original on 2012-05-24 . Retrieved 2012-05-02. Chlorine is intermediate in reactivity between fluorine and bromine, and is one of the most reactive elements. Chlorine is a weaker oxidising agent than fluorine but a stronger one than bromine or iodine. This can be seen from the standard electrode potentials of the X 2/X − couples (F, +2.866V; Cl, +1.395V; Br, +1.087V; I, +0.615V; At, approximately +0.3V). However, this trend is not shown in the bond energies because fluorine is singular due to its small size, low polarisability, and inability to show hypervalence. As another difference, chlorine has a significant chemistry in positive oxidation states while fluorine does not. Chlorination often leads to higher oxidation states than bromination or iodination but lower oxidation states than fluorination. Chlorine tends to react with compounds including M–M, M–H, or M–C bonds to form M–Cl bonds. [36]

Combined chlorine is the combination of organic nitrogen compounds and chloramines, which are produced as a result of the reaction between chlorine and ammonia. Chloramines are not as effective at disinfecting water as free chlorine due to a lower oxidation potential. Due to the creation of chloramines instead of free chlorine, ammonia is not desired product in the water treatment process in the beginning, but may be added at the end of treatment to create chloramines as a secondary disinfectant, which remains in the system longer than chlorine, ensuring clean drinking water throughout the distribution system. Chodos, Alan (ed.). "This Month in Physics History September 4, 1821 and August 29, 1831: Faraday and Electromagnetism". American Physical Society. Archived from the original on June 15, 2010 . Retrieved 2010-05-08. Chlorine pentafluoride (ClF 5) is made on a large scale by direct fluorination of chlorine with excess fluorine gas at 350°C and 250atm, and on a small scale by reacting metal chlorides with fluorine gas at 100–300°C. It melts at −103°C and boils at −13.1°C. It is a very strong fluorinating agent, although it is still not as effective as chlorine trifluoride. Only a few specific stoichiometric reactions have been characterised. Arsenic pentafluoride and antimony pentafluoride form ionic adducts of the form [ClF 4] +[MF 6] − (M = As, Sb) and water reacts vigorously as follows: [51] 2 H 2O + ClF 5 ⟶ 4 HF + FClO 2 Disinfection can also be done just prior to filtration and after sedimentation. This would control the biological growth, remove iron and manganese, remove taste and odours, control algae growth, and remove the colour from the water. This will not decrease the amount of biological growth in the sedimentation cells.Faraday, M. (1823). "On fluid chlorine". Philosophical Transactions of the Royal Society of London. 113: 160–64. Bibcode: 1823RSPT..113..160F. doi: 10.1098/rstl.1823.0016.

Chlorine Trifluoride for In Situ Cleaning of CVD Chambers in Semiconductor Manufacturing: Cons and Pros". Stanford Advanced Materials. 30 Aug 2023.The chlorine to ammonia nitrogen ratio characterizes what kind of residual is produced. Are there Other Uses for Chlorine? Most of the chlorine oxoacids may be produced by exploiting these disproportionation reactions. Hypochlorous acid (HOCl) is highly reactive and quite unstable; its salts are mostly used for their bleaching and sterilising abilities. They are very strong oxidising agents, transferring an oxygen atom to most inorganic species. Chlorous acid (HOClO) is even more unstable and cannot be isolated or concentrated without decomposition: it is known from the decomposition of aqueous chlorine dioxide. However, sodium chlorite is a stable salt and is useful for bleaching and stripping textiles, as an oxidising agent, and as a source of chlorine dioxide. Chloric acid (HOClO 2) is a strong acid that is quite stable in cold water up to 30% concentration, but on warming gives chlorine and chlorine dioxide. Evaporation under reduced pressure allows it to be concentrated further to about 40%, but then it decomposes to perchloric acid, chlorine, oxygen, water, and chlorine dioxide. Its most important salt is sodium chlorate, mostly used to make chlorine dioxide to bleach paper pulp. The decomposition of chlorate to chloride and oxygen is a common way to produce oxygen in the laboratory on a small scale. Chloride and chlorate may comproportionate to form chlorine as follows: [55] ClO − Labarraque's chlorinated lime and soda solutions have been advocated since 1828 to prevent infection (called "contagious infection", presumed to be transmitted by " miasmas"), and to treat putrefaction of existing wounds, including septic wounds. [76] In his 1828 work, Labarraque recommended that doctors breathe chlorine, wash their hands in chlorinated lime, and even sprinkle chlorinated lime about the patients' beds in cases of "contagious infection". In 1828, the contagion of infections was well known, even though the agency of the microbe was not discovered until more than half a century later. The product, chloryl fluoride, is one of the five known chlorine oxide fluorides. These range from the thermally unstable FClO to the chemically unreactive perchloryl fluoride (FClO 3), the other three being FClO 2, F 3ClO, and F 3ClO 2. All five behave similarly to the chlorine fluorides, both structurally and chemically, and may act as Lewis acids or bases by gaining or losing fluoride ions respectively or as very strong oxidising and fluorinating agents. [52] Chlorine oxides Yellow chlorine dioxide (ClO 2) gas above a solution containing chlorine dioxide. [ clarification needed] Structure of dichlorine heptoxide, Cl 2O 7, the most stable of the chlorine oxides Around 900, the authors of the Arabic writings attributed to Jabir ibn Hayyan (Latin: Geber) and the Persian physician and alchemist Abu Bakr al-Razi ( c. 865–925, Latin: Rhazes) were experimenting with sal ammoniac ( ammonium chloride), which when it was distilled together with vitriol (hydrated sulfates of various metals) produced hydrogen chloride. [7] However, it appears that in these early experiments with chloride salts, the gaseous products were discarded, and hydrogen chloride may have been produced many times before it was discovered that it can be put to chemical use. [8] One of the first such uses was the synthesis of mercury(II) chloride (corrosive sublimate), whose production from the heating of mercury either with alum and ammonium chloride or with vitriol and sodium chloride was first described in the De aluminibus et salibus ("On Alums and Salts", an eleventh- or twelfth century Arabic text falsely attributed to Abu Bakr al-Razi and translated into Latin in the second half of the twelfth century by Gerard of Cremona, 1144–1187). [9] Another important development was the discovery by pseudo-Geber (in the De inventione veritatis, "On the Discovery of Truth", after c. 1300) that by adding ammonium chloride to nitric acid, a strong solvent capable of dissolving gold (i.e., aqua regia) could be produced. [10] Although aqua regia is an unstable mixture that continually gives off fumes containing free chlorine gas, this chlorine gas appears to have been ignored until c. 1630, when its nature as a separate gaseous substance was recognised by the Brabantian chemist and physician Jan Baptist van Helmont. [11] [en 1] Carl Wilhelm Scheele, discoverer of chlorine Isolation

When used at specified levels for water disinfection, the reaction of chlorine with water is not a major concern for human health. Other materials present in the water may generate disinfection by-products that are associated with negative effects on human health. [115] [116] The right amount to add varies by product. In general, you’ll need to add about 4 pounds (1.8 kg) of cyuranic acid per 10,000 gallons (38,000 L) of water to reach a level of 10 ppm. It’s recommended to maintain a cyuranic acid level around 50 ppm. For swimming pools, it can be used in solid granular form (calcium hypochlorite) or liquid ( sodium hypochlorite). Most products you buy will be for about 10,000 gallons of pool water, so if your pool is larger than that, you will need more product.

Chlorination can be done at any time/point throughout the water treatment process - there is not one specific time when chlorine must be added. Each point of chlorine application will subsequently control a different water contaminant concern, thus offering a complete spectrum of treatment from the time the water enters the treatment facility to the time it leaves.

Unstabilized chlorine is the best choice for indoor pools or pools where there isn’t too much exposure to the sun, such as heavily shaded or covered areas. Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The N UBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode: 2003NuPhA.729....3A, doi: 10.1016/j.nuclphysa.2003.11.001Chlorination is one of many methods that can be used to disinfect water. This method was first used over a century ago, and is still used today. It is a chemical disinfection method that uses various types of chlorine or chlorine-containing substances for the oxidation and disinfection of what will be the potable water source. The History of Chlorination