|
|
Atomic Number: |
17 |
Melting Point: | -101.5 ºC | |
| Atomic Symbol: | Cl | Boiling Point: | -34.4 ºC | ||
| Atomic Weight: | 35.453 amu | Density: | 3.214
kg/m 3 |
||
| Atomic Radius: |
99 pm |
Oxidation States: | 7, 5, 1, -1 | ||
| Covalent Radius: | 99 pm | Electron Configuration: | [Ne]3s23p5 | ||
| van der Waals Radius: |
175 pm |
State of Matter: | gas (nonmagnetic) |
(Gr. chloros: greenish yellow) Discovered in 1774 by Scheele, who thought it contained oxygen. Chlorine was named in 1810 by Davy, who insisted it was an element.
It is a member of the halogen (salt-forming) group of elements and is obtained from chlorides by the action of oxidizing agents and more often by electrolysis; it is a greenish-yellow gas, combining directly with nearly all elements. At 10oC one liter of water dissolves 3.10 liters of chlorine, at 30oC only 1.77 liters.
In nature it is found in the combined state only, chiefly with sodium as common salt (NaCl), carnallite, and sylvite.
Chlorine can be manufactured via the electrolysis of a sodium chloride solution. There are three methods for the extraction of chlorine by electrolysis used industrially.
Mercury cell electrolysis was the first method used to produce chlorine on an industrial scale. Titanium anodes are located above a liquid mercury cathode, a solution of sodium chloride is positioned between the electrodes. When an electrical current is applied chloride is released at the titanium anodes, whilst the sodium dissolves into the mercury cathode forming an amalgam.
The amalgam can be regenerated into mercury by reacting it with water producing hydrogen and sodium hydroxide. These are useful byproducts. This method consumes vast amounts of energy and there are also concerns about mercury emissions.
In the diaphragm cell electrolysis, an asbestos diaphragm is deposited on an iron grid cathode preventing the chlorine forming at the anode and the sodium hydroxide forming at the cathode from re-mixing. This method uses less energy than the mercury cell, but the sodium hydroxide is not as easily concentrated and precipitated into a useful substance.
During a membrane cell electrolysis, the electrolysis cell is divided into two by a membrane acting as an ion exchanger. Saturated sodium chloride solution is placed in the anode compartment whilst distilled water is placed in the cathodes compartment. This method is nearly as efficient as the diaphragm cell and yet produces very pure sodium hydroxide.
Chlorine is widely used in making many everyday products. It is used for producing safe drinking water all over the world. Even the smallest water supplies are now usually chlorinated.
It is also extensively used in the production of paper products, dyestuffs, textiles, petroleum products, medicines, antiseptics, insecticides, food, solvents, paints, plastics, and many other consumer products.
Most of the chlorine produced is used in the manufacture of chlorinated compounds for sanitation, pulp bleaching, disinfectants, and textile processing. Further use is in the manufacture of chlorates, chloroform, carbon tetrachloride, and in the extraction of bromine.
Organic chemistry demands much from chlorine, both as an oxidizing agent and in substitution, since it often brings many desired properties in an organic compound when substituted for hydrogen, as in one form of synthetic rubber.
There are two principal stable isotopes of chlorine, of mass 35 and 37, found in the relative proportions of 3:1 respectively, giving chlorine atoms in bulk an apparent atomic weight of 35.5. Chlorine has 9 isotopes with mass numbers ranging from 32 to 40. Only three of these isotopes occur naturally: stable Cl-35 (75.77%)and Cl-37 (24.23%), and radioactive Cl-36.
Chlorine is a respiratory irritant. The gas irritates the mucus membranes and the liquid burns the skin. As little as 3.5 ppm can be detected as an odor, and 1000 ppm is likely to be fatal after a few deep breaths. In fact, chlorine was used as a war gas in 1915. Exposure to chlorine should not exceed 0.5 ppm (8-hour time-weighted average - 40 hour week.)
Acute exposure to high (but non-lethal) concentrations of Chlorine can result in Pulmonary Edema, or fluid in the lungs, an extremely unpleasant condition. Chronic low-level exposure weakens the lungs, increasing susceptibility to other lung disorders.
Toxic fumes may be produced when bleach is mixed with urine, ammonia or another cleaning product. These fumes consist of a mixture of chlorine gas and nitrogen trichloride; therefore these combinations should be avoided.
