What is chlorine


chlorine, Symbol Cl, chem. Element from main group VII of the periodic table, the group of halogens, non-metal; Z 17, mass numbers of the natural isotopes 35 (75.529%) and 37 (24.47%), atomic mass 35.453, valence -I, + I, + III to + VII, D. (at bp) 1.565, g cm-3 M.p. -101.00 ° C, b.p. -34.06 ° C, critical temperature 143.5 ° C, critical pressure 7.61 MPa, critical diameter 0.57 g cm-3, Standard electrode potential (Cl-/ Cl2) + 1.3595 V.

properties. C. is a suffocating, yellow-green, very reactive, Cl2-Molecule-forming, very toxic gas. At -34 ° C, when the pressure is increased also at room temperature (0.66 MPa, 20 ° C), it condenses to a yellow liquid. Liquefied C. comes in steel bottles on the market. Solid C. crystallizes in an orthorhombic molecular lattice. C. is readily soluble in water: 1 l of water dissolves 2.3 l at 20 ° C. Under the influence of sunlight, chlorinated water decomposes according to equations Cl2 + H2O

HCl + HOCl and HOCl

HCl + 1/2 O2. C. combines directly with all elements except carbon, oxygen, nitrogen and the noble gases. Base metals, above all alkali and alkaline earth metals, in finely divided state also relatively noble metals such as bismuth, arsenic or copper, combine with C., often at normal or slightly elevated temperatures, with strong heat development and mostly with the appearance of fire. So burns z. B. Sodium heated to 100 ° C in a stream of chlorine emitting intense yellow light to sodium chloride. The precious metals and other easily passivatable metals, e.g. B. chromium, tantalum or tungsten, are generally, especially in the compact state, only chlorinated when red heat. With non-metals, e.g. B. phosphorus, sulfur, iodine and hydrogen, C. reacts hardly or less vigorously at room temperature than with the base metals, but often quite violently at higher temperatures. So is z. B. an equimolar mixture of C. and hydrogen in the dark at room temperature unchanged, while it explodes in direct sunlight or when heated locally (chlorine gas). Moist C. is much more reactive than dry. Dry C. Iron only attacks above 270 ° C, so that it can be conducted in gaseous or liquid form through iron pipes or transported in steel cylinders and tank wagons. Tinplate can also be detinned because dry C. only reacts with tin to form liquid tin (IV) chloride, but leaves iron unaffected. Due to its great affinity for hydrogen, C. reacts with many hydrocarbon compounds, water, sulfur, bromine or hydrogen iodide to form HCl. C. has a destructive effect on complex organic compounds, primarily through oxidation and substitution reactions.

Chlorine is a lung poison that has a corrosive and inflammatory effect on the mucous membranes of the respiratory organs. More severe poisoning leads to convulsive cough and a feeling of suffocation, later to shortness of breath, pneumonia and lung bleeding. A concentration of 2.5 mg / l has an immediate effect, an amount of 0.15 mg / l is fatal after prolonged inhalation.

As a countermeasure in the event of chlorine poisoning, inhalation of water vapor is used. In the event of breathlessness, oxygen breathing or - but only in extreme emergencies - artificial respiration should be used. Consult a doctor.

Analytical. Free C. can be recognized by its odor and, in large concentrations, by its yellow-green color. C. colors potassium iodine starch paper blue. The reaction with silver nitrate is used for the qualitative and quantitative detection of chloride ions.

Occurrence. C. is involved in the structure of the earth's crust with 0.19%, is therefore one of the relatively common elements and takes 12th place on the frequency scale of the elements. In nature it is always bound, especially in the form of alkali and alkaline earth chlorides, in salt deposits and in sea water. The most important chlorine minerals are rock salt NaCl, Sylvin KCl, Carnallit KCl · MgCl2  · 6H2O, kainite KCl · MgSO4 · 3H2O and bishopite MgCl2 · 6H2O.