Characteristics and methods of obtaining chlorine, and its reaction with water
Interesting facts about a powerful oxidizer
Chlorine was first described in the “Treatise on Pyrolusite” by the Swedish chemist Scheele. The scientist heated the mineral pyrolusite with hydrochloric acid, and noticed a smell that was characteristic of aqua regia. He collected the yellow-green gas that caused this smell, and began to study its interaction with other substances. The chemist was the first to discover the bleaching properties of chlorine, and to notice the effect of chlorine on gold and cinnabar. The element was named by the scientist Davy, who studied the poisonous gas extensively.
General characteristics of chlorine
Chlorine is a halogen, a very powerful oxidizer, an extremely poisonous gas and an important product of the chemical industry. It is a raw material for the manufacture of toxic chemicals, plastics, artificial fiber, rubber, medicines and dyes. It is used to obtain silicon, titanium, fluoroplastic and glycerin. Chlorine is used to bleach fabrics and purify drinking water.
In ordinary conditions, chlorine is a heavy yellow-green gas with a characteristic smell. Its atomic weight is – 35.453, and its molecular weight is 70.906. One liter of chlorine in gaseous state in normal conditions weighs 3.214 g. If chlorine is cooled to a temperature of -34.05 degrees Celsius, the gas condensates into a yellow liquid, and at a temperature of -101.6 degrees Celsius, it becomes solid.
At high pressure, chlorine turns into a liquid even at higher temperatures. This gas has a high activity – it combines with almost every element in the periodic table. For this reason, in nature chlorine is encountered exclusively in the form of compounds. Chlorine is found in such minerals as halite, sylvinite, bishofite, carnallite and kainite. These minerals are “to blame” for the fact that the earth’s crust has a 0.17% chlorine content by weight. For non-ferrous metallurgy, such relatively rare minerals containing chlorine as horn silver are important. Liquid chlorine is among the strongest isolators of electrical conductivity – the substance conducts a current almost one million times worse than distilled water, and a thousand times worse than silver. The speed of sound in chlorine is 1.5 times less than in water.
At present, nine isotopes of chlorine are known to science, but in nature just 2 are encountered – chlorine-35 and chlorine-37. Chlorine-35 is three times more common than chlorine-37. Seven of the nine isotopes are obtained artificially. The shortest-lived isotope, chlorine-32, has a half-life of 0.306 second, and the longest-lived is chlorine-36, which can “live” for 310,000 years.
Methods of obtaining chlorine
The manufacture of chlorine requires a great deal of electricity to break down the natural compounds of the element. The main raw material for chlorine is ordinary rock salt, an inexpensive product that is used in large quantities (to obtain 1 ton of chlorine, at least 1.7 tons of salt is required). You can do an interesting and very easy experiment on obtaining chlorine through natrium chloride electrolysis even at home.
First the salt is crushed, then dissolved in warm water. The obtain solution is pumped into a purifying room, where potassium and magnesium salts are removed, and then it is clarified (allowed to settle). The pure concentrated solution of sodium chloride is pumped into a cell room.
There are two types of industrial production of chlorine: the mercury and diaphragm methods. In the second case, a perforated sheet of iron acts as the cathode, and the cathode and anode sections of the electrolytic cells are separated by an asbestos diaphragm. Hydrogen ions are discharged on the iron cathode, and a water solution of caustic sodium forms. When mercury is used as the cathode, sodium ions are discharged and a sodium amalgam forms, which is then broken down by water. Hydrogen and caustic sodium form. In this case the separating diaphragm is not needed, and the alkaline has a high concentration.
The manufacture of chlorine simultaneously involves the manufacture of hydrogen and caustic sodium. The hydrogen is removed in metal pipes, and the chlorine in ceramic or glass pipes. “Fresh” chlorine is saturated with water vapor, and for this reason displays its most aggressive properties. Chlorine is first cooled with cold water in towers lined with ceramic tiles, then dried with concentrated sulfuric acid, which is the only drying agent of chlorine which the element does not react with.
Dry chlorine is less aggressive and does not have a destructive effect on metal. Chlorine is transported in liquid state in cylinders under a pressure of up to 10 atmospheres, or in railway tanks. To compress and pump chlorine at factories, pumps with sulfuric acid are used, which also perform the role of a lubricant and working medium at the same time.
The reaction of chlorine with water
Chlorine dissolves in water, and at 20 degrees Celsius 2.3 volumes of chlorine dissolve in one volume of water. Initially, the water solution of chlorine is yellow, but if it is stored in light for a long time, the solution gradually loses its color. This is because the dissolved chlorine enters into a partial reaction with water, forming hydrochloric and hypochlorous acids. The chlorine solution in water gradually turns into a solution of hydrochloric acid, as hypochlorous acid is unstable and gradually breaks down into hydrogen chloride and oxygen.
At low temperatures, chlorine and water enter into a reaction and form a crystallohydrate of an unusual composition. These are crystals of a green-yellow color, which are only stable at a temperature below 10 degrees Celsius, and are formed when chlorine is passed through water containing ice. In the crystal structure of ice, water molecules can be arranged so that evenly positioned spaces appear between them. An elementary cubic cell contains 46 water molecules, with 8 microscopic spaces between them. The chlorine molecules settle in these spaces.