Physical and chemical characteristic of chlorine and its acidic compounds
How chlorine reacts with different compounds
Chlorine (Cl) is a chemical element with the atomic number 17 and an atomic mass of 35.453. Chlorine in free form is a heavy gas of a yellowy-green color with a suffocating, harsh smell.
Existence in nature and the history of its discovery
Chlorine is contained in the Earth’s crust, constituting 0.013% of its total mass. Chlorine is present in sea water in a significant concentration, in the form of the Cl ion – approximately 18.8g/l. Chemical chlorine has high activity, and is not encountered in nature in free form. Chlorine is present in the following minerals: rock salt (NaCl), carnallite (KCl·MgCl₂·6H₂O) and bischofite (MgCl₂·6H₂O). It is also found in soil and other rocks.
Chlorine was first obtained and described in 1774 by the Swedish chemist Karl Scheele. The scientist heated hydrochloric acid with mineral pyrolusite, and observed the release of a yellow-green gas with an unpleasant smell. Initially Scheele took the new gas to be an oxide of hydrochloric acid and called it “dephlogisticated hydrochloric acid”. Another scientist, Lavoisier, also believed that chlorine was an oxide of “muria” (hydrochloric acid). Only the English scientist Humphrey Davy, who tried many times to break down “muria oxide” into simple substances, established in 1811 that the poisonous green gas was a simple substance that corresponded to a chemical element. Here you’ll find an easy experiment on obtaining chlorine at home.
The chemical and physical properties of chlorine
In ordinary conditions, chlorine is a yellow-green gas, with a density exceeding the density of air by 2.5 times. The melting temperature of chlorine in a solid state is -100.98 degrees Celsius, and its boiling point is -33.97 degrees Celsius.
In a free state, chlorine is present in the form of diatomic molecules Cl₂. Chlorine is poorly soluble in water and highly soluble in many non-polar liquids.
Chlorine enters into an interaction with the majority of metals and many non-metals. For example, without heating chlorine enters into a reaction with alkaline and alkaline earth metals, and with antinomy. The equation of the reaction is:
2Sb + 3Cl₂ = 2SbCl₃
On heating, chlorine reacts with aluminum:
3Сl₂ + 2Аl = 2А1Сl₃,
2Fe + 3Cl₂ = 2FeCl₃.
With hydrogen, chlorine interacts either on ignition, or when a mixture of chlorine and hydrogen is exposed to ultraviolet light. Hydrogen chloride forms as a result:
Н₂ + Сl₂ = 2НСl
A solution of hydrogen chloride in water is called hydrochloric acid. At room temperature, chlorine interacts with sulfur and fluorine. On heating, chlorine interacts with phosphorous, arsenic, boron and other non-metals. Chlorine does not react directly with carbon and inert gases, oxygen and nitrogen. With other halogens, chlorine forms interhalogen compounds: for example, strong oxidizers — the fluorides ClF, ClF₃ and ClF₅.
The reaction of chlorine with oxygen — oxygen compounds of chlorine
Chlorine does not directly react with oxygen. But a number of compounds with this element can be obtained indirectly:
Hypochlorous acid HClO
It is a very weak monobasic acid, in which chlorine has the degree of oxidation of +1. It exists exclusively in solutions. In aqueous solutions, hypochlorous acid partially breaks down into protons and hypochlorite anions. It is unstable and gradually breaks down even in diluted aqueous solutions. Hypochlorous acid and its salts are hypochlorites, strong oxidizers. It reacts with hydrochloric acid, HCl, forming molecular chlorine. Hypochlorous acid forms in the dissolution of chlorine or chlorine oxide (I) in water (a disproportionate reaction). In industry, hypochlorites of calcium, sodium, potassium and lithium are manufactured by the chlorination of lime milk and corresponding alkalis. Hypochlorous acid and hypochlorites break down easily with the release of monatomic oxygen, and so they are widely used for whitening cellulose and fabrics, and also for medicinal purposes.
Chloric acid HClO₃
It is a strong monobasic acid, in which chlorine has the degree of oxidation of +5. It does not exist in free form, and in aqueous solutions in a concentration below 30% it is quite stable at cold temperatures, but in solutions of higher concentration it breaks down. No anhydride of chloric acid is known. When concentrated sulfuric acid reacts with KClO₃, a yellow-brown gas with a characteristic smell is released — chlorine dioxide ClO₂. This is a very unstable compound, which on heating, impact or contact with combustible substances easily breaks down with an explosion into chlorine and oxygen. Chloric acid resembles HNO₃ by its properties, and in a mixture with hydrochloric acid it is a strong oxidizer (of the same type as aqua regia). Chlorates, the salts of chloric acid (HCl₃), are strong oxidizers. The most important chlorates are Berthollet’s salt (KClO₃) and sodium chlorate (NaClO₃), used in the manufacture of dyes and matches, in medicine and fireworks, and in explosives and herbicides. The main consumers of NaClO₃ are the pulp and paper and textile industries, where the salt is used in the manufacture of chlorine dioxide – an effective whitening agent.
Perchloric acid HClO₄
It is a heavy, thick liquid, a monobasic acid. It contains chlorine atoms (Cl) at the highest degree of oxidation, is a very strong oxidizer, and is explosive. It is a volatile colorless liquid, which smokes strongly in air, and is monomeric in vapor. It is unstable and reactive. For perchloric acid, auto-dehydration is characteristic. It mixes well with water in any ratios. It forms several hydrates. Concentrated solutions of perchloric acid have a slightly oily consistency. Aqueous solutions of perchloric acid are stable, and have a low oxidation ability. Perchloric acid forms a azeotropic mixture with water, boiling at a temperature of 203 degrees Celsius and containing 72% HClO₄.