Phosphorus Phosphorus in nature obtaining properties of phosphorus. Areas of application of phosphorus. Getting and using phosphorus

DEFINITION

Phosphorus- the fifteenth element of the Periodic table. Designation - P from the Latin "phosphorus". Located in the third period, VA group. Refers to non-metals. The nuclear charge is 15.

Phosphorus is one of the fairly common elements; its content in the earth's crust is about 0.1% (wt.). Due to the easy oxidizability of phosphorus in the free state, it does not occur in nature.

Of the natural phosphorus compounds, the most important is calcium orthophosphate Ca 3 (PO 4) 2 , which sometimes forms large deposits in the form of the mineral phosphorine. The mineral apatite is also often found, containing, in addition to Ca 3 (PO 4) 2, also CaF 2 or CaCl 2.

Atomic and molecular weight of phosphorus

DEFINITION

Relative molecular weight of a substance (M r) is a number showing how many times the mass of a given molecule is greater than 1/12 of the mass of a carbon atom, and relative atomic mass of an element (A r)- how many times the average mass of atoms of a chemical element is greater than 1/12 of the mass of a carbon atom.

The values ​​of atomic and molecular weights of phosphorus coincide; they are equal to 30.9737.

Allotropy and allotropic modifications of phosphorus

Phosphorus forms several allotropic modifications.

White phosphorus is obtained in the solid state by rapid cooling of phosphorus vapor; its density is 1.83 g/cm 3 . In its pure form, white phosphorus is completely colorless and transparent (Fig. 1). It is brittle in the cold, but at temperatures above 15 o C it becomes soft and can be easily cut with a knife.

In air, white phosphorus oxidizes very quickly and glows in the dark. Already at low heating, for which simple friction is enough, phosphorus ignites and burns out. It has a molecular crystal lattice, in the nodes of which there are tetrahedral molecules P 4 . Strong poison.

Rice. 1. Allotropic modifications of phosphorus. Appearance.

If white phosphorus is heated to a temperature of 250-300 o C, it goes into another modification that has a red-violet color and is called red phosphorus. This transformation occurs very slowly and under the influence of light.

Red phosphorus in its properties is very different from white: it slowly oxidizes in air, does not glow in the dark, lights up only at 260 o C and is non-toxic.

With strong heating, red phosphorus, without melting, evaporates (sublimes). When the vapor is cooled, white phosphorus is obtained.

Black phosphorus is formed from white when heated to 200-220 o C under very high pressure. It looks like graphite, is greasy to the touch and heavier than other modifications. Semiconductor.

Isotopes of phosphorus

It is known that phosphorus occurs in nature in the form of a single isotope 31P (23.99%). The mass number is 31. The nucleus of an atom of the phosphorus isotope 31 P contains fifteen protons and sixteen neutrons.

There are artificial isotopes of phosphorus with mass numbers from 24 to 46, among which the most stable is 32 P with a half-life of 14 days.

Phosphorus ions

On the outer energy level of the phosphorus atom, there are five electrons that are valence:

1s 2 2s 2 2p 6 3s 2 3p 3 .

As a result of chemical interaction, phosphorus can lose its valence electrons, i.e. be their donor, and turn into positively charged ions or accept electrons from another atom, i.e. be their acceptor, and turn into negatively charged ions:

P 0 -5e → P 5+ ;

P 0 -3e → P 3+;

P 0 -1e → P 1+ ;

P 0 +3e → P 3- .

Molecule and atom of phosphorus

The phosphorus molecule is monatomic - R. Let us give some properties that characterize the atom and molecule of phosphorus:

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

• Designation - P (Phosphorus);
• Period - III;
• Group - 15 (Va);
• Atomic mass - 30.973761;
• Atomic number - 15;
• Radius of an atom = 128 pm;
• Covalent radius = 106 pm;
• Electron distribution - 1s 2 2s 2 2p 6 3s 2 3p 3 ;
• melt t = 44.14°C;
• boiling point = 280°C;
• Electronegativity (according to Pauling / according to Alpred and Rochov) = 2.19 / 2.06;
• Oxidation state: +5, +3, +1, 0, -1, -3;
• Density (n.a.) \u003d 1.82 g / cm 3 (white phosphorus);
• Molar volume = 17.0 cm 3 / mol.

Phosphorus compounds:

Phosphorus (carrying light) was first obtained by the Arab alchemist Ahad Behil in the 12th century. Of the European scientists, the German Hennig Brant was the first to discover phosphorus in 1669, during experiments with human urine in an attempt to extract gold from it (the scientist believed that the golden color of urine was caused by the presence of gold particles). Somewhat later, phosphorus was obtained by I. Kunkel and R. Boyle - the latter described it in his article "Method of preparing phosphorus from human urine" (10/14/1680; the work was published in 1693). Lavoisier later proved that phosphorus is a simple substance.

The content of phosphorus in the earth's crust is 0.08% by mass - this is one of the most common chemical elements on our planet. Due to its high activity, phosphorus in a free state does not occur in nature, but is part of almost 200 minerals, the most common of which are Ca 5 (PO 4) 3 (OH) apatite and Ca 3 (PO 4) 2 phosphorite.

Phosphorus plays an important role in the life of animals, plants and humans - it is part of such a biological compound as a phospholipid, it is also present in protein and other important organic compounds such as DNA and ATP.

Rice. The structure of the phosphorus atom.

The phosphorus atom contains 15 electrons, and has an external valence level electronic configuration similar to nitrogen (3s 2 3p 3), but phosphorus has less pronounced non-metallic properties compared to nitrogen, which is explained by the presence of a free d-orbital, a large atomic radius and lower ionization energy .

Entering into reactions with other chemical elements, the phosphorus atom can show an oxidation state from +5 to -3 (the most typical oxidation state is +5, the rest are quite rare).

• +5 - phosphorus oxide P 2 O 5 (V); phosphoric acid (H 3 PO 4); phosphates, halides, sulfides of phosphorus V (salts of phosphoric acid);
• +3 - P 2 O 3 (III); phosphorous acid (H 3 PO 3); phosphites, halides, sulfides of phosphorus III (salts of phosphorous acid);
• 0-P;
• -3 - phosphine PH 3; metal phosphides.

In the ground (unexcited) state, the phosphorus atom has two paired electrons in the s-sublevel + 3 unpaired electrons in the p-orbitals (the d-orbital is free) at the outer energy level. In the excited state, one electron from the s-sublevel passes to the d-orbital, which expands the valence possibilities of the phosphorus atom.

Rice. The transition of the phosphorus atom to an excited state.

P2

Two phosphorus atoms are combined into a P 2 molecule at a temperature of about 1000°C.

At lower temperatures, phosphorus exists in the four-atom molecules P 4 and also in the more stable polymer molecules P ∞ .

Allotropic modifications of phosphorus:

• White phosphorus- extremely poisonous (the lethal dose of white phosphorus for an adult is 0.05-0.15 g) waxy substance with the smell of garlic, without color, luminous in the dark (slow oxidation process in P 4 O 6); the high reactivity of white phosphorus is explained by weak P-P bonds (white phosphorus has a molecular crystal lattice with the formula P 4, at the nodes of which phosphorus atoms are located), which are quite easily broken, as a result of which white phosphorus, when heated or during long-term storage, passes into more stable polymer modifications: red and black phosphorus. For these reasons, white phosphorus is stored without air access under a layer of purified water or in special inert media.
• yellow phosphorus- a flammable, highly toxic substance, does not dissolve in water, easily oxidizes in air and ignites spontaneously, while burning with a bright green dazzling flame with the release of thick white smoke.
• red phosphorus- a polymeric, water-insoluble substance with a complex structure, which has the least reactivity. Red phosphorus is widely used in industrial production, because it is not so toxic. Since in the open air, red phosphorus, absorbing moisture, gradually oxidizes with the formation of a hygroscopic oxide (“damp”), forms viscous phosphoric acid, therefore, red phosphorus is stored in a hermetically sealed container. In the case of soaking, red phosphorus is cleaned of phosphoric acid residues by washing with water, then dried and used for its intended purpose.
• black phosphorus- greasy to the touch grey-black graphite-like substance with semiconductor properties - the most stable modification of phosphorus with an average reactivity.
• metallic phosphorus obtained from black phosphorus under high pressure. Metallic phosphorus conducts electricity very well.

Chemical properties of phosphorus

Of all the allotropic modifications of phosphorus, the most active is white phosphorus (P 4). Often, in the equation of chemical reactions, they simply write P, and not P 4. Since phosphorus, like nitrogen, has many variants of oxidation states, in some reactions it is an oxidizing agent, in others it is a reducing agent, depending on the substances with which it interacts.

Oxidative phosphorus exhibits properties in reactions with metals that occur when heated to form phosphides:
3Mg + 2P \u003d Mg 3 P 2.

Phosphorus is reducing agent in reactions:

• with more electronegative non-metals (oxygen, sulfur, halogens):
  • phosphorus (III) compounds are formed with a lack of an oxidizing agent
    4P + 3O 2 \u003d 2P 2 O 3
  • phosphorus (V) compounds - with an excess of: oxygen (air)
    4P + 5O 2 \u003d 2P 2 O 5
• with halogens and sulfur, phosphorus forms halides and sulfide of 3- or 5-valent phosphorus, depending on the ratio of reagents, which are taken in deficiency or excess:
  • 2P + 3Cl 2 (week) \u003d 2PCl 3 - phosphorus (III) chloride
  • 2P + 3S (weeks) \u003d P 2 S 3 - phosphorus (III) sulfide
  • 2P + 5Cl2 (ex.) \u003d 2PCl 5 - phosphorus (V) chloride
  • 2P + 5S (ex.) \u003d P 2 S 5 - phosphorus (V) sulfide
• with concentrated sulfuric acid:
  2P + 5H 2 SO 4 \u003d 2H 3 PO 4 + 5SO 2 + 2H 2 O
• with concentrated nitric acid:
  P + 5HNO 3 \u003d H 3 PO 4 + 5NO 2 + H 2 O
• with dilute nitric acid:
  3P + 5HNO 3 + 2H 2 O \u003d 3H 3 PO 4 + 5NO

Phosphorus acts as both an oxidizing agent and a reducing agent in reactions disproportionation with aqueous solutions of alkalis when heated, forming (except for phosphine) hypophosphites (salts of hypophosphorous acid), in which it exhibits an uncharacteristic oxidation state +1:
4P 0 + 3KOH + 3H 2 O \u003d P -3 H 3 + 3KH 2 P +1 O 2

REMEMBER: with other acids, except for the above reactions, phosphorus does not react.

Getting and using phosphorus

Industrially, phosphorus is produced by its reduction with coke from phosphorites (fluorapatates), which include calcium phosphate, by calcining in electric furnaces at a temperature of 1600 ° C with the addition of quartz sand:
Ca 3 (PO 4) 2 + 5C + 3SiO 2 = 3CaSiO 3 + 2P + 5CO.

At the first stage of the reaction, under the influence of high temperature, silicon (IV) oxide displaces phosphorus (V) oxide from phosphate:
Ca 3 (PO 4) 2 + 3SiO 2 \u003d 3CaSiO 3 + P 2 O 5.

Then phosphorus oxide (V) is reduced by coal to free phosphorus:
P 2 O 5 + 5C \u003d 2P + 5CO.

The use of phosphorus:

• pesticides;
• matches;
• detergents;
• paints;
• semiconductors.

STRUCTURE OF THE ATOM OF PHOSPHORUS

Phosphorus is located in the III period, in the 5th group of the main subgroup "A", under the serial number No. 15. Relative atomic mass A r (P) = 31 .

R +15) 2) 8) 5

1S 2 2S 2 2P 6 3S 2 3P 3, phosphorus: p - element, non-metal

The valence capabilities of phosphorus are wider than those of the nitrogen atom, since the phosphorus atom has free d-orbitals. Therefore, the depairing of 3S 2 - electrons can occur and one of them can go to the 3d - orbital. In this case, there will be five unpaired electrons in the third energy level of phosphorus and phosphorus will be able to show valence V.

In the free state, phosphorus forms several allotrocky modifications: white, red and black phosphorus

Phosphorus is present in living cells in the form of ortho- and pyrophosphoric acids; it is part of nucleotides, nucleic acids, phosphoproteins, phospholipids, coenzymes, and enzymes. Human bones consist of hydroxylapatite 3Ca 3 (PO 4) 3 ·CaF 2 . The composition of tooth enamel includes fluorapatite. The main role in the transformation of phosphorus compounds in humans and animals is played by the liver. The exchange of phosphorus compounds is regulated by hormones and vitamin D. The daily human need for phosphorus is 800-1500 mg. With a lack of phosphorus in the body, various bone diseases develop.

PHOSPHORUS TOXICOLOGY

· red phosphorus practically non-toxic. Dust of red phosphorus, getting into the lungs, causes pneumonia with chronic action.

· White phosphorus very toxic, soluble in lipids. The lethal dose of white phosphorus is 50-150 mg. Getting on the skin, white phosphorus causes severe burns.

Acute phosphorus poisoning is manifested by burning in the mouth and stomach, headache, weakness, and vomiting. After 2-3 days, jaundice develops. Chronic forms are characterized by a violation of calcium metabolism, damage to the cardiovascular and nervous systems. First aid for acute poisoning - gastric lavage, laxatives, cleansing enemas, intravenous glucose solutions. In case of skin burns, treat the affected areas with solutions of copper sulfate or soda. MPC of phosphorus vapor in the air is 0.03 mg/m³.

OBTAINING PHOSPHORUS

Phosphorus is obtained from apatites or phosphorites as a result of interaction with coke and silica at a temperature of 1600 ° C:

2Ca 3 (PO 4) 2 + 10C + 6SiO 2 → P 4 + 10CO + 6CaSiO 3 .

The resulting white phosphorus vapor condenses in the receiver under water. Instead of phosphorites, other compounds can be reduced, for example, metaphosphoric acid:

4HPO 3 + 12C → 4P + 2H 2 + 12CO.

CHEMICAL PROPERTIES OF PHOSPHORUS

APPLICATIONS OF PHOSPHORUS

Phosphorus is the most important biogenic element and at the same time is very widely used in industry.

Perhaps the first property of phosphorus, which man put to his service, is flammability. The combustibility of phosphorus is very high and depends on the allotropic modification.

The most active chemically, toxic and combustible white ("yellow") phosphorus, therefore it is very often used (in incendiary bombs, etc.).

red phosphorus- the main modification produced and consumed by the industry. It is used in the production of matches, together with finely ground glass and glue, it is applied to the side surface of the box, when the match head is rubbed, which includes potassium chlorate and sulfur, ignition occurs. Red phosphorus is also used in the production of explosives, incendiary compositions, and fuels.

Phosphorus (in the form of phosphates) is one of the three most important biogenic elements involved in the synthesis of ATP. Most of the produced phosphoric acid is used to obtain phosphate fertilizers - superphosphate, precipitate, etc.

TASKS FOR REINFORCEMENT

No. 2. Carry out the transformations according to the scheme:
P -> Ca 3 P 2 -> PH 3 -> P 2 O 5
For the last reaction PH 3 -> P 2 O 5 draw up an electronic balance, indicate the oxidizing agent and reducing agent.

No. 3. Carry out the transformations according to the scheme:
Ca 3 (PO 4 ) 2 -> P -> P 2 O 5

Phosphorus is a chemical element with atomic number 15. It is located in group V of the D.I. Mendeleev. The chemical formula of phosphorus R.

Phosphorus got its name from the Greek phosphoros, which means "light-bearing".

Phosphorus is quite common in the earth's crust. Its content is 0.08-0.09% of the entire mass of the earth's crust. And in sea water, phosphorus contains 0.07 mg / l.

Phosphorus has a high chemical activity, therefore, it does not occur in the free state. But on the other hand, it forms almost 190 minerals. Phosphorus is called the element of life. It is found in green plants, animal tissues, proteins and other essential chemical compounds.

Phosphorus modifications

It is known that some chemical elements can exist in the form of two or more simple substances that differ in their structure and properties. This phenomenon is called allotropy. So, phosphorus has several allotropic modifications. All these modifications are different in their properties. The most common are white phosphorus, yellow phosphorus, red phosphorus, black phosphorus.

White phosphorus - a simple white substance. Its molecular formula is P 4 . In appearance, white phosphorus is similar to paraffin. It deforms even with little effort and is easily cut with a knife. In the dark, a pale green glow emanating from phosphorus is noticeable. This phenomenon is called chemiluminescence.

White phosphorus is a chemically active substance. It is easily oxidized by oxygen and readily soluble in organic solvents. Therefore, it is stored in special inert media that do not enter into chemical reactions. White phosphorus melts at +44.1 °C. White phosphorus is a highly toxic substance.

yellow phosphorus - this is crude white phosphorus, or white phosphorus with impurities. Melting point +34 °C, boiling point +280 °C. Like white, yellow phosphorus is insoluble in water. Oxidizes in air and flammable. He also has the phenomenon of chemiluminescence.

red phosphorus obtained by heating white phosphorus to high temperatures. Formula of red phosphorus Р n . It is a complex polymer. Depending on the production conditions, the color of red phosphorus can vary from light red to dark brown. Chemically, red phosphorus is much less active than white. It dissolves only in molten lead and bismuth. Does not ignite in air. This can only happen when heated to 240-250 o C when it is sublimated into the white form of phosphorus. But it can ignite spontaneously on impact or friction. The phenomenon of chemiluminescence in red phosphorus is not observed. It is insoluble in water, benzene, carbon disulfide. Soluble only in phosphorus tribromide. When stored in air, it gradually oxidizes. Therefore, store it in a closed sealed container.

Red phosphorus is almost non-toxic. Therefore, it is he who is used in the production of matches.

black phosphorus looks like graphite. For the first time, black phosphorus was obtained in 1914 from white phosphorus at a pressure of 20 thousand atmospheres (2 10 9 Pa) and a temperature of 200 o C. Black phosphorus melts at a temperature of 1000 o C and a pressure of 18 10 5 Pa. Black phosphorus does not dissolve in water or in organic solvents. It starts to burn only if it is heated to a temperature of +400 ° C in pure oxygen. Black phosphorus has the properties of semiconductor materials.

Chemical properties of elemental phosphorus

1. Elemental phosphorus is oxidized by oxygen

In an environment with excess oxygen

4P + 5O 2 → 2P 2 O 5

With a lack of oxygen

4P + 3O 2 → 2P 2 O 3

2. Reacts with metals, forming phosphides when heated

3Mg + 2P → Mg 3 P 2

3. Reacts with non-metals

2P + 5Cl 2 → 2PCl 5

4. At a temperature of +500 ° C interacts with water vapor

8P + 12H 2 O → 5RN 3 + 3H 3 RO 4

The use of phosphorus

The main consumer of phosphorus is agriculture. A large amount of all phosphorus obtained is used for the production of phosphate fertilizers: phosphate rock, simple and double superphosphates, complex nitrogen-phosphorus fertilizers. Phosphorus is widely used in the production of synthetic detergents, phosphate glasses, for processing and dyeing natural and synthetic fibers. In medicine, phosphorus preparations are used as medicines.

PHOSPHORUS, P, element of group V of the periodic system; atomic weight 31.03; Phosphorus isotopes have not been found. In compounds, phosphorus is trivalent and pentavalent. Its highest connection with hydrogen is PH 3; with oxygen, it gives the oxides P 2 O 3, P 2 O 4 and P 2 O 5. In terms of valence and type of compounds, phosphorus resembles nitrogen, but in properties (both phosphorus and its compounds) it is completely different from nitrogen. common in nature and found in almost all rocks in the form of inclusions of crystals of the mineral apatite. Phosphorus is found in the form of mineral accumulations of phosphorites and apatites. Apatites rarely occur in large masses, and the colossal deposits of this mineral in the Khibiny tundra in the USSR are an exception. Phosphorites are known in Georgia, Florida, North and South Carolina, Tennessee, Algeria, Tunisia, and on some islands of the Great Ocean. The USSR is extremely rich in phosphorites, the deposits of which are known in the Moscow region, in the Urals, in Kazakhstan, in Ukraine, in the Chuvash Republic, in Podolia, in the North Caucasus, etc. Minerals such as vivianite Fe 3 (PO 4) 2 8H 2 O and turquoise (Al 2 O 3) 2 P 2 O 5 5H 2 O are aqueous salts of phosphoric acid. Phosphorus is an indispensable component, part of the tissues of living organisms. Proteins containing phosphorus and lecithin are part of the muscles, nerves and brain. Bones contain phosphorus in the form of tricalcium salt of phosphoric acid.

Phosphorus can be obtained in several allotropic modifications. White phosphorus (ordinary, yellow) is a colorless, transparent vitreous substance or white small crystals; pure white phosphorus can only be obtained in the dark in the absence of oxygen and moisture. Fractional distillation or fractional crystallization results in completely pure phosphorus, which quickly turns yellow in the light. Such yellowing is explained by the formation of a thin film of red modification on the surface of phosphorus. With prolonged exposure to intense light on ordinary phosphorus, it can be completely converted to red. At 150°C in the absence of oxygen, ordinary phosphorus sublimates without changing color. Two modifications are known for white phosphorus - α and β; the first crystallizes in the correct system (specific gravity 1.84), the second (ordinary phosphorus) - in hexagonal (specific gravity 1.88). The transition of α-phosphorus to β-phosphorus occurs under the following conditions:

Mohs hardness of phosphorus is 0.5. Its plasticity increases with increasing temperature. Molten phosphorus hardly wets the glass; surface tension 35.56 D/cm at 132.1°C and 43.09 D/cm at 78.3°C. The corresponding specific gravities of phosphorus are 1.665 and 1.714. The compressibility of ordinary phosphorus between 100 and 500 atm is 0.0000199 cm 2 /kg. The expansion coefficient of ordinary phosphorus from 0°C to 40° = 0.000125, and its volume at 44°C is 1.017 times the volume at 0°C. Heat capacity of white phosphorus (0-51°C) 0.183 cal/g; heat of fusion 5.03 cal/g. The weight of 1 liter of phosphorus vapor is 2.805 g (Williamson). Its molar weight in the range of temperatures from 313 ° C to red heat ranges from 128 to 119.8. Therefore, the structure of its molecule in this interval corresponds to P 4 . At high temperatures, it partially dissociates into P 2 . In solution, its molecule corresponds to the formula P 4; melting point of ordinary phosphorus 44.5°C; it slowly sublimates at 40°C, evaporates at normal temperature. Vapor pressure of ordinary solid phosphorus at 5°C - 0.03 mm, at 40°C - 0.50 mm. Solubility of phosphorus in water: 0.0003 g per 100 g of water at 15°C. Various solvents dissolve approximately phosphorus (in 100 hours of solvent): carbon disulfide 25, gasoline 1.5, almond oil 1.00, concentrated acetic acid 1.00, ether 0.45, ethyl alcohol (specific gravity 0.822) 0.25, glycerin 0.17 h. Hydrogen is well absorbed by phosphorus, especially during an electric discharge. Hydrogen is able to react with phosphorus in statu nascendi; the released gas no longer possesses this ability. Fluorine reacts at ordinary temperature with phosphorus without ignition, forming PF 3 with an excess of phosphorus and PF 5 with an excess of fluorine. Phosphorus combines vigorously with oxygen, forming, depending on the amount of reagents, phosphorous or phosphoric anhydride. Hydroquinone, sugar, glycerin, sodium arsenic acid slow down the oxidation reaction of phosphorus. Combining with atmospheric oxygen, phosphorus ignites, so it must be stored under water. The ignition temperature of phosphorus in air, in oxygen or in air diluted with an equal volume of carbon dioxide is 45.0-45.2°C. The ignition of ordinary phosphorus is promoted by rarefaction of the air and is prevented by compression. The presence of ozone and moisture in the atmosphere increases the ignition temperature. In an atmosphere of carbon disulfide, the ignition temperature of phosphorus is 87 ° C, turpentine - 18 °; phosphorus can be heated without ignition to 205°C if it is at rest; the slightest stirring causes ignition even at 45°C. Ordinary phosphorus ignites within 20 seconds when brought into contact with pure amalgamated aluminium. Nitrogen is absorbed by phosphorus, but does not react with it. White phosphorus glows in the dark when it comes into contact with atmospheric oxygen. The intensity of the glow depends on the concentration of oxygen. In pure oxygen below 27°C, phosphorus does not glow and does not oxidize. White phosphorus is poisonous and a dose of 0.15 g is lethal. In view of the ability of phosphorus to dissolve in fats, in case of poisoning, fatty foods and milk are completely unacceptable as they contribute to a better absorption of phosphorus into the body.

Red phosphorus is a modification that differs sharply in its physical and chemical properties from white phosphorus. Red phosphorus is formed from ordinary when an electric discharge is passed through the vapors of the latter. By heating a solution of white phosphorus in phosphorus tribromide at a temperature of 170-190 ° C, one can isolate the so-called. raspberry variety phosphorus. This variety has a colloidal structure and is transitional between ordinary and red phosphorus; the presence of phosphorus triiodide accelerates (3 times) the reaction. By heating ordinary phosphorus with sulfur or sulfide, and then treating the resulting mixture with an aqueous solution of alkali or ammonia, red phosphorus can also be obtained. Red phosphorus in technology is obtained by heating ordinary phosphorus without air at a temperature of 240-250 ° C; The reaction is accompanied by the release of heat. The color of red phosphorus changes depending on the temperature of the preparation. At low temperatures, it has a crimson hue, at high temperatures, it is violet or purple. Selenium accelerates the transition of white phosphorus to red. The separation of the admixture of ordinary phosphorus from red is carried out by treatment with carbon disulfide for 50 hours at 250-260 ° C or 10% sodium alkali solution for 2 hours; it is also possible to wash phosphorus with a mixture of carbon disulfide and calcium chloride solution with a specific gravity of 1.349-1.384. In this case, ordinary phosphorus dissolves in carbon disulfide, and red settles into a solution of calcium chloride. There is an assumption that the white and red modifications of phosphorus are chemically different; the proof of this position is that when molten yellow and red phosphorus are mixed, no transition of the first into the second is observed. When heated within the range of 280-400 ° C, red phosphorus vapor partially thickens into the so-called. metallic phosphorus. With the rapid cooling of vapors, partially red phosphorus is formed, and the greater the amount, the higher the temperature was before solidification. The surface of the receiver acts catalytically on the formation of red phosphorus. The duration of heating does not affect the process, but cooling should occur quickly. There is an opinion (A. Stock) that red phosphorus is formed as a result of the combination of dissociated phosphorus molecules with each other or with non-dissociated molecules and that the formation of P 4 yellow phosphorus molecules is relatively slower than the formation of red phosphorus molecules. The condensation of red phosphorus from the vapor state is independent of the presence of liquid yellow phosphorus. Red phosphorus, obtained by cooling vapors that had a temperature of 1200 ° C, and at a pressure of 5 mm, contains no more than 1% yellow phosphorus; hence it follows that the P 2 and P 4 molecules take part in the formation of red phosphorus. It is possible that this formation follows the equation mР 2 + nP 4 = P 2 m+4 n. There are suggestions that the molten phosphorus contains P 4 molecules of yellow phosphorus and P n molecules of red phosphorus in equilibrium:

Above the melting point of red phosphorus (592.5°C, according to other sources 589.5°C), most of the molecules are in the form of P 4, so that a white variety forms on rapid cooling, but slow cooling allows the equilibrium to shift to the right, and red phosphorus is released during solidification. The specific gravity of red phosphorus ranges from 2.05 to 2.3, which makes us consider it as a mixture of two modifications. There is an assumption that red phosphorus is monoclinic in its crystal structure. The compressibility of red phosphorus (between 100-500 atm) is 0.0000092 cm 2 /kg; The melting point of red phosphorus depends on the heating rate and varies within ±0.5°C. Vapor pressure of red phosphorus at 230°C - 0 mm, at 360°C - 0.1 mm, at 500°C - 9 atm. Red phosphorus is insoluble in carbon disulfide. Red phosphorus obtained with the release of heat contains less energy and is much less active than white phosphorus. Red phosphorus is not poisonous, it does not ignite in air, which is why its storage is not so dangerous. Red phosphorus ignites on impact. Gittorf claims that the transition of red phosphorus to yellow is not observed at a temperature of 320 ° C, but the latter is formed at 358 ° C. In a sealed tube, red phosphorus is strong at temperatures from 450 to 610°C.

Crystalline, or violet, phosphorus has a crystalline structure, the crystals are trigonal with an axial ratio a:c = 1:1.1308. It is obtained by crystallization from molten lead or bismuth, as well as by heating white phosphorus under a pressure of 500 kg / cm 2 in the presence of sodium. Insoluble in carbon disulfide; specific gravity of violet phosphorus 2.34; it sublimates at 690.9°C; melting point 589.5°C at a pressure of 43.1 atm.

Black phosphorus (R. Bridgeman) is obtained from ordinary phosphorus when heated to 216 ° C under a pressure of 89 atm. It is insoluble in carbon disulfide; ignites at a temperature of 400 ° C and does not ignite on impact; the transition temperature of red phosphorus to black 575°C; red phosphorus turns into black when heated in a hydrogen atmosphere at 200°C and a pressure of 90 atm (V. Ipatiev). Only 2 modifications are of technical importance: white (yellow) and red phosphorus.

Getting phosphorus. White phosphorus is usually prepared, which, if necessary, is subsequently converted into a red modification. The starting material for obtaining phosphorus is phosphorites - natural tricalcium phosphate, best of all bone ash. The process consists in the reduction of phosphate with carbon or the action of aluminum on sodium metaphosphate mixed with silica:

6NaPO 3 + 3SiO 2 + 10Al \u003d 3Na 2 SiO 3 + 5Al 2 O 3 + 6P.

There are 2 methods of factory production of phosphorus: 1) the old Pelletier method, which consists in treating phosphate (bone meal) with dilute sulfuric acid, and tricalcium phosphate is converted into monocalcium phosphate:

Ca 3 (PО 4) 2 + 2H 2 SO 4 \u003d 2CaSO 4 + Ca (H 2 PО 4) 2.

The solution of the latter is separated from gypsum (CaSO 2H 2 O), evaporated, calcined with coal and calcium metaphosphate is obtained:

Ca (H 2 RO 4) 2 \u003d 2H 2 O + Ca (RO 3) 2,

which after strong calcination gives phosphorus, tricalcium phosphate and carbon monoxide:

ZCa (RO 3) 2 + 10C \u003d Ca 3 (RO 4) 2 + 4P + 10CO.

According to the Wehler method, they proceed directly from tricalcium phosphate:

2Ca 3 (PO 4) 2 + 6SiO 2 + 10C \u003d 6CaSiO 3 + 10CO + 4P.

This process requires a high temperature and began to be used only with the introduction of electric furnaces. There is also a method for obtaining phosphorus from free phosphoric acid mixed with coal using electric current. Academician in the USSR. E. V. Britske developed a method for obtaining phosphorus in blast furnaces.

Commercial product always contains traces of arsenic, silicon compounds and carbon. Mechanical impurities are removed by filtration, and even better by re-distillation. The transformation of white phosphorus into red is carried out at a temperature of 260°C; a decrease in pressure slows down the course of the reaction; lighting speeds up the process; catalysts (iodine, selenium) also affect.

Analytical determination of phosphorus. Phosphorus vapor acts on wet paper impregnated with silver nitrate, causing it to blacken. The blackness is due to the formation of phosphorous and metallic silver . The reaction proceeds in 2 stages. Phosphorus reacts with water to form hydrogen phosphorous and hypophosphorous acid:

P 4 + 6H 2 O \u003d ZN 3 RO 2 + PH 3.

The compounds resulting from the reaction act on silver nitrate:

H3PO 2 +2H 2 O + 4AgNO 3 \u003d 4HNO 3 +H3PO 4 +4Ag;

PH 3 + 3AgNO 3 \u003d 3HNO 3 + PAg 3.

This reaction is applicable for the discovery of white phosphorus only in the absence of H 2 S, AsH 3 , SbH 3 , as well as formic aldehyde and formic acid. The discovery of poisonous phosphorus (according to Mitcherlich) is based on the ability of phosphorus to glow in humid air in the dark. The crushed substance, in which phosphorus is supposed to be discovered, is placed in a flask connected to a refrigerator. So much water is poured into the flask to obtain a liquid slurry, and the contents of the flask are neutralized with tartaric acid until slightly acidic. When the flask is heated in the dark, an insignificant amount of phosphorus (a few mg) already causes a glow in the refrigerator. Since the phenomenon of luminescence may also be due to the presence of phosphorus sulfide after its decomposition upon heating, it is recommended that the flask be heated not directly, but by passing water vapor into it. The glow of phosphorus is not observed in the presence of traces of ammonia, carbon disulfide, alcohol vapors, essential oils and unsaturated hydrocarbons, so the distillation should not be stopped too early. If, nevertheless, no glow is observed, then the filtrate is oxidized with chlorine water, evaporating in a water bath to a small volume, and a test is made for phosphoric acid. The glow of phosphorus can also be observed in the flask, heating the liquid first to a boil, then cooling it slightly and heating it again to a boil; 0.0171 mg of phosphorus glow very clearly, 0.0085 mg - clearly, 0.0042 mg - weakly and 0.001 mg - doubtful. Phosphorus, being reduced by hydrogen in statu nascendi, gives hydrogen phosphorous, which, mixed with hydrogen, burns with an emerald-green flame when ignited at the outlet of a platinum-tipped tube. Organic substances prevent the appearance of color, and therefore d. b. separated. Nitric acid easily oxidizes phosphorus to phosphoric acid:

ZR 4 +20NNO 3 +8H 2 O \u003d 12H 3 RO 4 +20NO3.

Phosphorus is quantified after oxidation to phosphoric acid and precipitation as MgNH 4 PO 4 .

Application . Phosphorus is one of the elements without which the proper development of plant and animal organisms is impossible. There is a direct relationship between the content of phosphorus in the nutrient medium and plant growth. Phosphorus, along with nitrogen and potassium, is the most important nutrient in which the page - x. plants. Being alienated from the field along with the grain harvest, phosphorus does not have a closed cycle in its cycle, and therefore, without its artificial introduction into the soil from the outside, soil depletion is observed. Fertilizers containing phosphorus make up the largest group. Phosphorus is used in military affairs as a smoke-generating agent and for filling incendiary projectiles.