Phosphorus and its compounds: oxidation states, formulas
Phosphorus and its compounds are widely distributed in the crust and seawater. As a chemical element, it belongs to the group of pnictides, which means that it belongs to the 15th group of the Periodic System. The activity of the element is very high, it forms almost 200 natural minerals, is contained in animal tissues, is part of the proteins, fats, molecules that exchange energy and store hereditary information in the body.
Phosphorus (P) is a non-metal, it exists in 11 allotropic modifications, differing in color, density, chemical properties. The main ones are 4:
- greenish white (yellow);
- the black;
The remaining forms are not yet fully understood, but it is believed that they are a mixture of the four main ones. Major modifications can also go into each other, as they are unstable. For example, white phosphorus under the action of light turns into red, which, in turn, into black, and then into metallic.The latter form is stable, but with each transformation the chemical activity of the substance decreases.
This allotropic modification is represented by P molecules.4. It is metastable, softens to room wax at room temperature, and becomes brittle in the cold. Melting and boiling take place without decomposition, the air oxidizes the substance and makes it glow. It can be distilled with steam, low heat leads to volatilization, and the presence of oxygen at the same time provides ignition even under water.
Dissolve the white form in organic compounds: carbon disulfide, chlorides and bromides of trivalent phosphorus, ammonia, sulfur dioxide, dithiodichloride. It is difficult to dissolve in tetrachloride, it is not sensitive to the effects of water, it is well preserved under its layer.
The substance can be obtained by the reaction of calcium orthophosphate with coke and silica at 1000 degrees Celsius. Another method is the decomposition of phosphorus triiodide at a temperature of 100-120 degrees Celsius.
The activity of white phosphorus is very high: it restores precious metals from their salts, is oxidized by acids, hydrogen peroxide, permanganate, halogens and chalcogenes. Restored by hydrogen and metals.Interaction with alkalis leads to a disproportionation reaction. Substances to which white phosphorus is inert are carbon and nitrogen.
High chemical activity makes the modification dangerous. It spontaneously ignites on contact with skin, resulting in severe burns. In addition, poisoning with white phosphorus leads to the defeat of the bones, up to their death, and the accumulation in the body of 50-150 mg leads to death.
Untreated white phosphorus is called yellow. Its color varies from light to dark brown. The substance can only be stored and transported under a layer of water or calcium chloride solution, since it is flammable and toxic, oxidized by oxygen in the air, which causes it to ignite, accompanied by burning of a bright green flame and the release of thick white smoke.
To extinguish the fire, you need a very large amount of ice water, but it is better to use a solution of copper sulfate. In order to avoid re-ignition, the already extinguished hearth should be additionally filled with wet sand.
This modification consists of polymer molecules Pndifferent sizes.It is metastable and X-ray amorphous, sublimates when heated. Its chemical activity is weak. Like white phosphorus, this form is oxidized in air, but the process is much slower and auto-ignition is not observed until the temperature reaches 240 degrees, or the substance is subjected to friction. In the presence of moisture, the red form is converted to an oxide, and then to phosphoric acid. Because of this, it is stored in an airtight container, but if the conversion does take place, it is washed with water from the residual chemical compounds of phosphorus and dried.
Carbon disulfide, like water, is not able to dissolve the red modification, but phosphorus tribromide and the melt of bismuth or lead, from which the violet form P later crystallizes, can make it8.
Red phosphorus is obtained by heating white in an atmosphere of carbon monoxide at a temperature of 500 degrees Celsius. Depending on the degree of crushing, there may be variations in the color from purple-red to dark purple with a metallic sheen. The process can go in the opposite direction: if you translate the red modification into steam, then cool down, it will turn into white.
The use of red phosphorus and its compounds is wide. First of all, this is due to the fact that they are substantially less toxic than those of the white form. They are used in the production of matches, as they ignite from friction.
Black and metallic phosphorus
This modification can be confused with graphite, as it has the appearance of black shiny crystals with metallic luster and a layered structure. To the touch they are fat. Black phosphorus consists of continuous chains Pn. It is chemically passive, stable in air, and does not dissolve in water or in organic compounds. It can be set on fire only by burning in an atmosphere of pure oxygen. In this case, he conducts an electric current. It turns out black phosphorus from white when heated above 200 degrees and under a pressure of 13-20 thousand atmospheres. In the metal turns at 820 thousand atmospheres.
Phosphorus and its compounds form almost two hundred minerals. The most famous of them is apatite. In nature, it may look different. Often it is similar to beryl, diopside or tourmaline. Because of this, they gave him the name, which is translated from Greek as “deception”. Apatite can be distinguished by its lower hardness compared to other minerals and prismatic appearance of crystals.
There are few deposits of this resource, the largest is in Russia, the rest are dispersed in Brazil, Mexico, America, Chile and other countries. Application it is in industry and in agriculture. It acts as a component of fertilizer, ceramics, glass.
Because of the fragility of the jewelers use this stone rarely, and it is usually of interest only to collectors. The largest apatite of good quality had a mass of 147 carats, but usually these minerals do not go beyond 5-20 carats.
Apatite is also found in living organisms, where it forms part of the bones and teeth and can be deposited in the kidney stones.
The degree of oxidation of phosphorus
In compounds, the element exhibits a positive or negative oxidation state, and in a simple substance P4it is zero.
The negative oxidative number -3 is manifested in phosphine and phosphides. The phosphorus exhibits a positive oxidation state in the compounds:
- hypophosphorous acid and its salts phosphinates (+1);
- phosphorous acid and phosphites (+3);
- phosphoric anhydride, a number of halides, phosphoric acid (+5).
These are only examples of substances that contain phosphorus.In fact, the formulas of phosphorus compounds are much larger, and an element can exhibit different oxidation numbers in them, for example, there are halides in which its oxidation state is 3. Each of these substances has its own unique properties, which determine their use by humans.
PH3- gaseous hydrogen compound of phosphorus, called phosphine or monophosphane. It is poorly soluble in water, does not react with alkalis and ammonia hydrate. It is a strong reducing agent, interacts with concentrated acids, iodine, oxygen, hydrogen peroxide, sodium hypochlorite. It is in this compound that the degree of oxidation of phosphorus is -3.
In its pure form, the substance is poisonous, inhibits the nervous system and disrupts metabolism. However, it is colorless and odorless. Technical samples emit the smell of rotten fish. You can get them from various compounds, for example:
- from tricalcium diphosphide when it reacts with water (catalysts in the form of hydrogen and diphosphine are required), either diluted with hydrochloric or unconcentrated orthophosphoric acids;
- from white phosphorus in its reaction with concentrated alkali and water (the reaction proceeds faster when boiling), or with hydrogen under pressure and at a temperature of 300 - 360 degrees Celsius, or with hydrochloric acid at 300 degrees;
- from phosphonium iodide when it decomposes under the influence of a temperature of 80 degrees (the reverse reaction takes place when cooled to minus 20 degrees), or when it interacts with water or dilute alkali;
- from phosphonic acid at its decomposition in vacuum at a temperature of 100 degrees and subsequent heating to 200 degrees in the presence of diphosphine, or by its reaction with atomic hydrogen obtained by the interaction of zinc with dilute sulfuric acid.
Natural phosphine ignites spontaneously in air, which gives the effect of "wandering lights" in the form of a ball or a candle flame. This rare occurrence can sometimes be seen in swamps, fields, or cemeteries.
The phosphorus compound of the formula H (PH2ABOUT2) also called phosphinic or hypophosphorous acid. Previously, it was designated as H3Ro2, but it turned out that such a spelling is incorrect, since the acid is monobasic. This is the compound in which the degree of oxidation of phosphorus is 1.
The substance has a white color, it is low melting and decomposes already with weak heating.Among its other properties - good solubility in water, neutralization with alkalis and ammonia hydrate, the ability to act as a strong reducing agent when heated in a concentrated solution or a weak oxidizing agent.
You can get it in the following ways:
- by the reaction of white phosphorus with concentrated barium hydroxide and water when heated to 70 degrees Celsius, followed by the addition of diluted cold sulfuric acid to the obtained salt;
- the interaction of phosphine with water and iodine;
- adding cationic water to sodium phosphinate.
The resulting substance allows you to create durable metal coatings for glass, ceramics or plastics, and its salts are used in the pharmaceutical industry.
Another name for the phosphorus compound is H2(RNO3) - phosphonic acid. As in the previous case, the wrong spelling of H used to be practiced.3Ro3, but it was abandoned because the acid is dibasic in aqueous solutions.
The degree of oxidation of phosphorus in the compound is equal to 3. The substance has a white color, decomposes when heated, slowly oxidizes in air, dissolves in water.The acid is weak and is easily neutralized by alkalis; it can act as a weak oxidizing agent or a not very strong reducing agent. Most reactions require heating.
There are many ways to produce acid, for example:
- the reaction of phosphorus with concentrated sulfuric or selenous acid (in the latter case, water is required);
- oxidation of wet phosphorus with oxygen (to accelerate the reaction requires heating to 30-40 degrees);
- the interaction of phosphine with concentrated sulfuric acid;
- adding water or gaseous hydrochloric acid to tetraphosphorus hexaoxide (the reaction will go faster if the water is hot);
- the interaction of phosphorus trichloride with water at room temperature (the reaction can be carried out at 0 degrees, but in this case, liquid carbon tetrachloride is required);
- the reaction of phosphorus triiodide with water in a nitrogen atmosphere.
In the following, the reducing properties of the compound are used.
R4ABOUT10called phosphoric anhydride. It can be in an amorphous, vitreous or crystalline state, and its color is always white. The crystalline substance is sublimated when heated,in order for it to start melting, it is necessary to create an overpressure, and then the anhydride will turn into a highly mobile fluid.
If the temperature treatment continues, a polymerization process will occur, as a result of which, crystalline decaoxide will turn into a glassy product of composition after cooling (P2ABOUT5)n. The degree of oxidation of phosphorus in the compound p2o5, as in P4ABOUT10equals 5.
Other possible chemical reactions of this compound:
- interaction with water and alkalis, which characterizes its acidic properties;
- halogenization, namely the replacement of oxygen atoms with fluorine, chlorine, bromine or iodine;
- phosphorus recovery;
- the formation of peroxocompounds.
However, the most important property of a substance is its ability to split water from molecules of organic compounds (dehydration). Due to this, phosphoric anhydride has been widely used as a desiccant for gases and liquids. In addition, it is used in organic synthesis and is an intermediate in the thermal production of phosphoric acid.
The substance can be obtained in the following ways:
- burning white phosphorus in air at a temperature of 34-60 degrees Celsius (you can take the red version, but in this case requires 240-400 degrees);
- the interaction of white phosphorus with chlorite and dilute sodium hydroxide at a temperature of 10-15 degrees;
- by the reaction of red phosphorus with potassium chlorate at a temperature of 50 degrees;
- by oxidation of tetraphosphorus hexaoxide with oxygen at a temperature of from 50 to 120 degrees.
For industrial production most often use the first method. The technological process takes place in a special chamber with dried air. The decaoxide obtained is purified by sublimation.
PF5- colorless gas. In the compound, phosphorus exhibits an oxidation state of 5, which is the most characteristic of the element. The substance boils without decomposition, but the process can begin with further heating. It hydrolyzes with water, reacts with alkalis, hydrogen fluoride, and silicon dioxide. Forms fluorocomplexes.
The methods for its preparation are as follows:
- the rapid decomposition of red phosphorus at a temperature of minus 60 degrees with fluorine in excess of argon as a catalyst;
- the interaction of phosphorus pentachloride with calcium fluoride at 300-400 degrees or with liquid arsenic fluoride at room temperature.
The compound obtained is used in the production of fluorophosphates, as well as a metal corrosion inhibitor.
Thus, phosphorus and its compounds are of great importance in industry and are used in various industries.