How to make phosphorus at home. Orthophosphoric acid

A more accurate name for this substance is phosphoric acid, which, when evaporated, has the form of colorless diamond-shaped crystals, whose melting point is 42.3 ° C. In its pure form, it is quite rare, and therefore 75 - 85 percent aqueous solution of phosphorus is called phosphoric acid. The chemical formula of the described acid H3PO4. Phosphoric acid can be mixed with H2O in any ratio, thus obtaining a slightly acidic solution. Thus, this substance, being in its usual form, is a colorless, odorless, thick liquid.

Under normal conditions, this acid is inactive and reacts with only a small amount of metals, hydroxides and carbonates. If the substance is heated to a temperature of more than 80 ° C, inactive oxides, silicates and silica can be used for reactions with it. Also, during heating, water evaporates from the acid, forming first pyrophosphoric, and then metaphosphoric acids.

Phosphorus is an indispensable element for all living organisms on planet Earth, regardless of whether it is a microorganism, a simple plant or a person. He is singled out the most important role in the growth of bones, teeth, shells in animals and claws.

The use of phosphoric acid

The scope of phosphorus compounds is truly huge, below is a list of some of them:

Fertilizer production.

For these purposes, most of the entire extracted phosphoric acid is used. Every year, more than 90 percent of phosphorus-containing ore is used worldwide in the production of fertilizers alone. The main producers of fertilizers of this type include Russia, the USA and Morocco, while the main consumers include almost all Western European, Asian and African countries.

Salts of phosphoric acid are consumed by plants in the form of anions, as well as salts of polyphosphoric acids during hydrolysis. Phosphorus is used by plants in the formation of their most important parts, namely seeds and fruits. Also, due to phosphoric acid, the winter hardiness of plants increases, they become more resistant to drought. A particularly important condition is the use of phosphorus-containing fertilizers in the northern regions with a short growing season. It also has a beneficial effect on the soil itself, causing the active development of soil bacteria.

Food industry.

Solutions of the described acid are used to flavor syrups, all kinds of carbonated drinks and marmalades. This substance is registered as a food additive E338. Salts of phosphoric acid can improve the taste of various bakery products.

Fur farming.

An indispensable substance for the prevention of kidney stones and hyperacidity of the stomach is phosphoric acid.

Woodworking industry.

Phosphoric acid solutions are used in the woodworking industry to impregnate wood, making the wood non-combustible.

Production of building materials and household chemicals.

Flame-resistant paints and varnishes are produced using this acid, such as: enamel, varnish and impregnations, as well as fire-resistant phosphate foam, boards made of wood and other building materials.

Phosphoric acid salts are used to soften water, and they are also found in detergents and descalers.

Phosphoric acid production

In small quantities, phosphoric acid is easily obtained in laboratory conditions by oxidizing phosphorus with a solution of 32% nitric acid. Under industrial conditions, it is obtained by means of an extraction and thermal method.

The extraction method is considered less expensive. Its essence lies in the decomposition of natural phosphates with the help of various acids, the most commonly used is sulfuric, as well as nitric and hydrochloric. This method involves extracting P2O5 into the following view - H3PO4. For these purposes, phosphates are processed H2SO4, and the resulting pulp is filtered from the precipitated Ca sulfate. Thus, pure phosphoric acid is obtained.

The list of rather high requirements is imposed on the raw materials used in the production of phosphoric acid, for example, natural phosphates containing carbonates in large quantities, compounds of Al, Mg, Fe and other organic substances are unsuitable! On the territory of the Russian Federation and the CIS countries, in the production of phosphoric acid, the Khibiny apatite concentrate is most often used along with Karatau phosphorites.

The thermal method used to obtain the purest acid consists of several stages: combustion of elemental phosphorus, hydration P4O10 and absorption by water, condensation and capture of gas. Depending on the applied principle of gas cooling, there are three types of thermal acid production:

Evaporative;
circulating-evaporative;
heat exchange and evaporative.

Domestic enterprises most often resort to the use of technology with a circulation-evaporative cooling method.

In contact with

Usually, the date of discovery of phosphorus is considered to be 1669, but there are some indications that it was known earlier. Gefer, for example, reports that in an alchemical manuscript from a collection stored in the Paris Library, it is said that around the 12th century. a certain Alkhid Bekhil obtained a substance by distillation of urine with clay and lime, which he called "escarbucle". Perhaps this was phosphorus, which is the great secret of the alchemists. In any case, it is known that in search of the philosopher's stone, alchemists subjected to distillation and other operations all kinds of materials, including urine, feces, bones, etc.

Since ancient times, phosphors have been called substances that can glow in the dark. In the 17th century Bolognese phosphorus was known - a stone found in the mountains near Bologna; after burning on coals, the stone acquired the ability to glow. It also describes "Baldwin's phosphorus", prepared by the volost foreman Alduin from a calcined mixture of chalk and nitric acid. The glow of such substances caused extreme surprise and was considered a miracle.

In 1669, the Hamburg amateur alchemist Brand, a bankrupt merchant who dreamed of improving his affairs with the help of alchemy, processed a wide variety of products. Assuming that physiological products might contain the "primordial matter" thought to be the basis of the Philosopher's Stone, Brand became interested in human urine.

Oh, how he was carried away by the idea, what efforts he made to implement it! Believing that the products of the vital activity of a person, the “king of nature”, can contain the so-called primary energy, the tireless experimenter began distilling human urine, one might say, on an industrial scale: in the soldiers’ barracks, he collected a whole ton of it in total! And he evaporated to a syrupy state (not in one go, of course!), And after distillation, he again distilled the resulting “urine oil” and calcined it for a long time. As a result, white dust appeared in the retort, which settled to the bottom and glowed, which is why it was called “cold fire” (kaltes Feuer) by Brand. Brand's contemporaries called this substance phosphorus because of its ability to glow in the dark (other Greek jwsjoroV).

In 1682, Brand published the results of his research, and he is now rightly considered the discoverer of element No. 15. Phosphorus was the first element whose discovery was documented, and its discoverer is known.

Interest in the new substance was enormous, and Brand took advantage of this - he demonstrated phosphorus only for money or exchanged small amounts of it for gold. Despite numerous efforts, the Hamburg merchant could not fulfill his cherished dream - to obtain gold from lead using "cold fire", and therefore he soon sold the recipe for obtaining a new substance to a certain Kraft from Dresden for two hundred thalers. The new owner managed to make a much larger fortune on phosphorus - he traveled all over Europe with "cold fire" and demonstrated it to scientists, high-ranking and even royal people, for example, Robert Boyle, Gottfried Leibniz, Charles II. Although the method of preparing phosphorus was kept in the strictest confidence, in 1682 Robert Boyle managed to obtain it, but he also disclosed his method only at a closed meeting of the Royal Society of London. Boyle's method was made public after his death, in 1692.

In the spring of 1676, Kraft arranged a session of experiments with phosphorus at the court of Elector Friedrich Wilhelm of Brandenburg. At 9 pm on April 24, all the candles in the room were extinguished, and Kraft showed those present experiments with "eternal fire", without revealing, however, the method by which this magical substance was prepared.

In the spring of the following year, Kraft came to the court of Duke Johann Friedrich in Hannover3, where at that time the German philosopher and mathematician G.W. Leibniz (1646-1716) served as a librarian. Kraft also arranged a session of experiments with phosphorus here, showing, in particular, two flasks that glowed like fireflies. Leibniz, like Kunkel, was extremely interested in the new substance. At the first session, he asked Kraft if a large piece of this substance would not be able to light up the whole room. Kraft agreed that it was quite possible, but would be impractical, since the process of preparing the substance is very complicated.

Who had this? I had.

Leibniz's attempts to persuade Kraft to sell the secret to the duke failed. Then Leibniz went to Hamburg to Brand himself. Here he managed to conclude a contract between Duke Johann Friedrich and Brand, according to which the former was obliged to pay Brand 60 thalers for revealing the secret. From that time on, Leibniz entered into regular correspondence with Brand.

At about the same time, I.I. Becher (1635-1682) arrived in Hamburg with the aim of luring Brand to the Duke of Mecklenburg. However, Brand was again intercepted by Leibniz and taken to Hanover to Duke Johann Friedrich. Leibniz was fully convinced that Brand was very close to discovering the "philosopher's stone", and therefore advised the duke not to let him go until he had completed this task. Brand, however, stayed in Hanover for five weeks, prepared fresh supplies of phosphorus outside the city, showed, according to the contract, the secret of production and left.

Then Brand prepared a significant amount of phosphorus for the physicist Christian Huygens, who studied the nature of light, and sent a supply of phosphorus to Paris.

Brand, however, was very dissatisfied with the price Leibniz and Duke Johann Friedrich gave him for revealing the secret of phosphorus production. He sent an angry letter to Leibniz, complaining that the amount received was not enough even to support his family in Hamburg and pay travel expenses. Similar letters were sent to Leibniz and Brand's wife, Margarita.

Brand was also dissatisfied with Kraft, to whom he expressed resentment in letters, reproaching him for having resold the secret for 1000 thalers to England. Kraft forwarded this letter to Leibniz, who advised Duke Johann Friedrich not to irritate Brand, to pay him more generously for revealing the secret, fearing that the author of the discovery, in the form of an act of revenge, would share the recipe for making phosphorus with someone else. Leibniz sent a reassuring letter to Brand himself.

Apparently, Brand received a reward, tk. in 1679 he again came to Hanover and worked there for two months, receiving a weekly salary of 10 thalers with additional payment for the table and travel expenses. Correspondence between Leibniz and Brand, judging by the letters kept in the Hanover Library, continued until 1684.

Let us now return to Kunkel. According to Leibniz, Kunkel learned through Kraft the recipe for making phosphorus and set to work. But his first experiments were unsuccessful. He wrote letter after letter to Brand, complaining that he had been sent a recipe that was very incomprehensible to another person. In a letter written in 1676 from Wittenberg, where Kunkel was then living, he asked Brand about the details of the process.

In the end, Kunkel achieved success in his experiments, somewhat modifying Brand's method. By adding a little sand to dry urine before distilling it, he received phosphorus and ... made a claim to the independence of the discovery. In the same year, in July, Kunkel spoke about his successes to his friend, Professor of Wittenberg University Kaspar Kirchmeyer, who published a work on this issue under the title "Permanent night lamp, sometimes sparkling, which was long sought, now found." In this article, Kirchmeyer speaks of phosphorus as a long-known luminous stone, but does not use the term "phosphorus" itself, obviously not yet accustomed to that time.

In England, independently of Brand, Kunkel and Kirchmeier in 1680, phosphorus was obtained by R. Boyle (1627-1691). Boyle knew about phosphorus from the same Kraft. As early as May 1677, phosphorus was demonstrated at the Royal Society of London. In the summer of the same year, Kraft himself came with phosphorus to England. Boyle, according to his own account, visited Kraft and saw phosphorus in his solid and liquid form. In gratitude for the warm welcome, Kraft, saying goodbye to Boyle, hinted to him that the main substance of his phosphorus was something inherent in the human body. Obviously, this hint was enough to give an impetus to Boyle's work. After Kraft's departure, he began to test blood, bones, hair, urine, and in 1680 his efforts to obtain a luminous element were crowned with success.

Boyle began to exploit his discovery in the company of an assistant, the German Gaukwitz. After Boyle's death in 1691, Gaukwitz launched the production of phosphorus, improving it on a commercial scale. By selling phosphorus at three pounds sterling an ounce and supplying the scientific institutions and individual scientists of Europe with it, Gaukwitz amassed a huge fortune. To establish commercial connections, he traveled to Holland, France, Italy and Germany. In London itself, Gaukwitz founded a pharmaceutical company that became famous during his lifetime. It is curious that, despite all his experiments with phosphorus, sometimes very dangerous, Gaukwitz lived to be 80 years old, outliving his three sons and all the people who participated in the work related to the early history of phosphorus.

Since the discovery of phosphorus by Kunkel and Boyle, it has rapidly fallen in price as a result of the competition of inventors. In the end, the heirs of the inventors began to acquaint everyone with the secret of its production for 10 thalers, all the while lowering the price. In 1743, A.S. Marggraf found an even better way to produce phosphorus from urine and immediately published it, because. fishing has ceased to be profitable.

Currently, phosphorus is not produced anywhere by the Brand-Kunkel-Boyle method, since it is completely unprofitable. For the sake of historical interest, we will nevertheless give a description of their method.

Rotting urine is evaporated to a syrupy state. The resulting thick mass is mixed with three times the amount of white sand, placed in a retort equipped with a receiver, and heated for 8 hours on an even fire until the volatile substances are removed, after which the heating is increased. The receiver is filled with white vapor, which then turns into bluish solid and luminous phosphorus.

Phosphorus got its name due to the property to glow in the dark (from Greek - luminiferous). Among some Russian chemists there was a desire to give the element a purely Russian name: "gem", "lighter", but these names did not take root.

Lavoisier, as a result of a detailed study of the combustion of phosphorus, was the first to recognize it as a chemical element.

The presence of phosphorus in the urine gave chemists a reason to look for it in other parts of the body of animals. In 1715, phosphorus was found in the brain. The significant presence of phosphorus in it served as the basis for the assertion that "without phosphorus there is no thought." In 1769, Yu.G. Gan found phosphorus in the bones, and two years later, K.V. Scheele proved that the bones consist mainly of calcium phosphate, and proposed a method for obtaining phosphorus from the ash remaining after bones were burned. Finally, in 1788, M.G. Klaproth and J.L. Proust showed that calcium phosphate is an extremely widespread mineral in nature.

The allotropic modification of phosphorus - red phosphorus - was discovered in 1847 by A. Schretter. In a work entitled "A New Allotropic State of Phosphorus", Schretter writes that sunlight changes white phosphorus to red, and factors such as dampness, atmospheric air, have no effect. Schretter separated the red phosphorus by treatment with carbon disulfide. He also prepared red phosphorus by heating white phosphorus to a temperature of about 250 ° C in an inert gas. At the same time, it was found that a further increase in temperature again leads to the formation of a white modification.

It is very interesting that Schroetter was the first to predict the use of red phosphorus in the match industry. At the World Exhibition in Paris in 1855, red phosphorus, already obtained by the factory, was demonstrated.

The Russian scientist A.A. Musin-Pushkin in 1797 received a new modification of phosphorus - violet phosphorus. This discovery is erroneously attributed to I.V. Gittorf, who, having almost completely repeated the Musin-Pushkin method, received violet phosphorus only in 1853.

In 1934, Professor P.W. Bridgman, subjecting white phosphorus to a pressure of up to 1100 atm, turned it into black and thus obtained a new allotropic modification of the element. Along with the color, the physical and chemical properties of phosphorus have changed: white phosphorus, for example, ignites spontaneously in air, and black, like red, does not have this property.

sources

water, and not with other phosphate anions. In the solutions of phosphoric acid, there is an exchange of oxygen atoms between PO 4 groups and water.

H 3 PO 4 - strong acid, K 1 7.1 10 -3 (pK a 2.12), K 2 6.2 10 -8 (pK a 7.20), K 3 5.0 10 -13 (pK a 12.32); the values of K 1 and K 2 depend on the t-ry. Dissociation in the first stage is exothermic, in the second and third - endothermic. The phase diagram of the H 3 PO 4 - H 2 O system is shown in fig. 2. The maximum of the crystallization curve is at t-re 302.4 K and the content of H 3 PO 4 91.6% (solid phase - hemihydrate). In table. St. Islands solutions of phosphoric acid are given.

CHARACTERISTICS OF H 3 PO 4 AQUEOUS SOLUTIONS


		T. shutter, 0 C	T. b., 0 C	kJ/(kg K)	Pa s (25 0 C)	Oud. electric conductivity, S/m (25 0 C)
H3PO4	P2O5	T. shutter, 0 C	T. b., 0 C	kJ/(kg K)	Pa s (25 0 C)	Oud. electric conductivity, S/m (25 0 C)
5	3,62	0,8	100,10	4,0737	0,0010	10,0	3129,1
10	7,24	2,10	100,20	3,9314	0,0011	18,5	3087,7
20	14,49	6,00	100,80	3,6467	0,0016	18,3	2986,4
30	21,73	11,80	101,80	3,3411	0,0023	14,3	2835,7
40	28,96	21,90	103,90	3,0271	0,0035	11,0	2553,1
50	36,22	41,90	104,00	2,7465	0,0051	8,0	2223,8
60	43,47	76,9	114,90	2,4995	0,0092	7,2	1737,1
70	50,72	43,00	127,10	2,3278	0,0154	6,3	1122,6
75	54,32	17,55	135,00	2,2692	0,0200	5,8	805,2

F osphoric acid under normal conditions is inactive and reacts only with carbonates, hydroxides and certain metals. In this case, one-, two- and three-substituted phosphates are formed (see Inorganic phosphates). When loading above 80 0 C reacts even with inactive oxides, silica and silicates. At elevated temperatures, phosphoric acid is a weak oxidizing agent for metals. When acting on a metal a surface solution of phosphoric acid with additions of Zn or Mn forms a protective film (phosphating). Phosphoric acid at heating. loses water with the formation of successively pyro- and metaphosphoric acids:

Phospholeum (liquid phosphoric anhydride, superphosphoric acid) includes to-you containing from 72.4 to 88.6% P 2 O 5, and is an equilibrium system consisting of ortho-, pyro-, Tripoli-, tetrapoly- and other phosphoric to-t (see Condensed phosphates). When diluted with superphosphorus water, it stands out. amount of heat, and polyphosphoric to-you quickly turn into orthophosphoric.

From other phosphoric to-t H 3 PO 4 can be distinguished by p-tion with AgNO 3 - a yellow precipitate Ag 3 PO 4 falls. The remaining phosphoric acids form white precipitates.

Receipt. Phosphoric acid in the lab. conditions, it is easy to obtain by oxidation of phosphorus with a 32% solution of nitric acid:

In the industry, phosphoric acid is obtained by thermal and extraction methods.

Thermal method (allows you to produce the most pure phosphoric acid) includes DOS. stages: combustion (oxidation) of elemental phosphorus in excess air, hydration and absorption of the resulting P 4 O 10 (see Phosphorus oxides), condensation of phosphoric acid and trapping of fog from the gas phase. There are two ways to obtain P 4 O 10: the oxidation of P vapor (rarely used in the industry) and the oxidation of liquid P in the form of drops or films. The degree of oxidation P in prom. conditions is determined by t-swarm in the oxidation zone, diffusion of components, and other factors. The second stage of obtaining thermal. phosphoric acid - hydration P 4 O 10 - is carried out by absorption to-that (water) or mutual mod. vapor P 4 O 10 with water vapor. Hydration (P 4 O 10 + 6H 2 O4H 3 PO 4) proceeds through the stages of formation of polyphosphoric acids. The composition and concentration of the resulting products depend on the temperature and partial pressure of water vapor.

All stages of the process can be. combined in one apparatus, except for catching fog, a cut is always produced in a separate apparatus. In the industry, schemes of two or three mains are usually used. devices. Depending on the principle of gas cooling, there are three ways to produce thermal. phosphoric acid: evaporative, circulation-evaporative, heat exchange-evaporative. Evaporate systems based on the removal of heat during the evaporation of water or dil. phosphoric acid, max. simple in hardware design. However, due to the relatively large volume of exhaust gases, the use of such systems is advisable only in installations of small unit capacity.

Circulating-evaporate. systems allow to combine in one apparatus the stages of burning P, cooling the gas phase of the circulating to-one and hydration P 4 O 10 . The disadvantage of the circuit is the need to cool large volumes of k-you. Heat exchange-evaporate. systems combine two methods of heat removal: through the wall of the combustion and cooling towers, as well as by evaporating water from the gas phase; a significant advantage of the system is the absence of circulation circuits to-you with pumping and refrigeration equipment.

On the fatherlands. enterprises operate technology. schemes with circulation-evaporate. cooling method (two-tower system). Distinguish. scheme features: the presence of additionalnit. gas cooling towers , use of efficient plate heat exchangers in circulation circuits ; high performance application. nozzles for burning P, providing a uniform fine atomization of a jet of liquid P and its complete combustion without the formation of lower oxides.

Technol. Figure 1 shows a diagram of a plant with a capacity of 60,000 tons per year of 100% H 3 PO 4 . 3. Molten yellow phosphorus is atomized with heated air at a pressure of up to 700 kPa through a nozzle in a combustion tower irrigated by a circulating filter. Heated in the tower to-that is cooled by circulating water in plate heat exchangers. Productive to-ta, containing 73-75% H 3 PO 4 is discharged from the circulation circuit to the warehouse. In addition, the cooling of gases from the combustion tower and absorption to-you are carried out in the cooling tower (hydration), which reduces the afterbirth, the temperature load on the electrostatic precipitator and contributes to effective gas purification. Heat removal in the hydration tower is carried out by circulating 50% H 3 PO 4 cooled in plate heat exchangers. Gases from the hydration tower after being cleaned from H 3 PO 4 mist in a plate electrostatic precipitator are released into the atmosphere. For 1 ton of 100% H 3 PO 4, 320 kg of P is consumed.

Rice. 3. Circulation double-tower scheme for the production of thermal. H 3 PO 4: 1 - sour water collector; 2 - storage of phosphorus; 3.9 - circulation collectors; 4.10 - submersible pumps; 5.11 - plate heat exchangers; 6 - combustion tower; 7 - phosphorus nozzle; 8 - hydration tower; 12 - electrostatic precipitator; 13 - fan.

A more economical extraction method for obtaining phosphoric acid is based on the decomposition of nature. phosphates to-tami (mainly sulfuric, to a lesser extent nitric and slightly hydrochloric). Phosphoric acid solutions obtained by decomposition of nitric acid are processed into complex fertilizers, by decomposition of hydrochloric acid - into precipitate.

Sulfuric acid decomposition of phosphate raw materials [in the CIS countries Ch. arr. Khibiny apatite concentrate (see Apatite) and Karatau phosphorites] - main. method for obtaining extraction phosphoric acid, used for the production of conc. phosphate and complex fertilizers. The essence of the method is the extraction (extraction) of P 4 O 10 (usually f-lu P 2 O 5 is used) in the form of H 3 PO 4 . According to this method, phosphates are treated with H 2 SO 4 followed by filtration of the resulting pulp to separate phosphoric acid from the Ca sulfate precipitate. Part of the selected core. the filtrate, as well as the entire filtrate obtained by washing the precipitate on the filter, is returned to the extraction process (dilution solution) to ensure sufficient mobility of the pulp during its mixing and transportation. Mass ratio between liquid and solid phases from 1.7:1 to 3.0:1.

Natural phosphates decompose according to the scheme:

Accompanying impurities are also decomposed to-tami: calcite, dolomite, siderite, nepheline, glauconite, kaolin and other minerals. This leads to an increase in the consumption of used to-you, and also reduces the extraction of P 2 O 5 in the target product due to the formation of insoluble iron phosphates FeH 3 (PO 4) 2 2.5H 2 O at P 2 O 5 concentrations above 40% (content P 4 O 10 is usually given in terms of P 2 O 5) and FePO 4 · 2H 2 O - at lower concentrations. I single outCO 2, which is released during the decomposition of carbonates, forms stable foam in extractors; p-rime phosphates of Mg, Fe and Al reduce the activity of phosphoric acid, and also reduce the content of assimilable forms of P 2 O 5 in fertilizers during the last. processing of phosphoric acid.

Taking into account the influence of impurities, the requirements for phosphate raw materials are determined, according to Crimea prir. phosphates with a high content Comm. Fe, Al, Mg, carbonates and org. in-in unsuitable for the production of phosphoric acid.

Depending on the temperature and concentration of phosphoric acid in the CaSO 4 -H 3 PO 4 -H 2 O system, Ca sulfate precipitates as dihydrate (gypsum), hemihydrate or anhydrite. In real conditions, the precipitate is contaminated with P 2 O 5 impurities in the form of undecomposed nature. phosphates, underwashed H 3 PO 4 , co-crystallized phosphates decomp. metals, etc., so the resulting Ca sulfates called. resp. phosphogypsum, phosphohemihydrate and phospho-anhydrite. Depending on the type of precipitated sulfate, there are three direct methods for the production of extraction phosphoric acid: dihydrate, hemihydrate (hemihydrate) and anhydrite, as well as combined: hemihydrate-dihydrate and dihydrate-hemihydrate.

In the CIS, naib. the dihydrate method has been worked out in the industry, to-ry it is distinguished by a high yield of P 2 O 5 (93-96.5%) in the production to-that; however relatively lowWhat concentration of phosphoric acid requires its last. evaporation. Main process steps: extraction with ext. or int. circulation and vacuum or air cooling of the extraction pulp, ripening of the pulp after the extractor, separation of phosphoric acid on bulk vacuum filters. The efficiency of the process is determined in the main.

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) \u003d 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 to form 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 purified from phosphoric acid residues by washing with water, then dried and used for its intended purpose.
black phosphorus- greasy to the touch graphite-like substance of gray-black color, 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 obtained 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.

Content

Fans of the carbonated drink "Coca-Cola" are unlikely to look at its composition, which has the addition of E338. This substance is phosphoric acid, which is used not only in the food industry, but also in textile, agricultural, and even copes with rust on the surface of parts. What are the properties of a chemical compound, what are the areas of its use, what you need to know about safety - it is worth considering in more detail.

What is phosphoric acid

At room temperature, these are hygroscopic, colorless, diamond-shaped crystals that are readily soluble in water. An orthophosphorus compound is considered an inorganic acid with medium strength. One of its forms, a yellowish or colorless syrupy liquid, odorless, is an aqueous solution with a concentration of 85%. Its other name is white phosphoric acid.

The chemical orthophosphorus compound has the following properties:

soluble in ethanol, water, solvents;
forms 3 rows of salts - phosphates;
causes burns on contact with skin;
when interacting with metals, it forms combustible, explosive hydrogen;
the boiling point depends on the concentration - from 103 to 380 degrees;
the liquid form is prone to hypothermia;
incompatible with combustible materials, pure metals, quicklime, alcohol, calcium carbide, chlorates;
at a temperature of 42.35 degrees it melts, but does not decompose.

Formula

Orthophosphoric acid is an inorganic compound, which is described by the formula H3PO4. Its molar mass is 98 g/mol. A microparticle of a substance is built in space in such a way that it connects the atoms of hydrogen and oxygen. The formula shows that the chemical has the following composition:

Getting phosphoric acid

A chemical compound has several production methods. A well-known industrial method for the manufacture of phosphoric acid is thermal, which produces a pure high-quality product. The following process takes place:

oxidation during combustion with excess air of phosphorus to phosphoric anhydride having the formula P4O10;
hydration, absorption of the resulting substance;
phosphoric acid condensation;
capturing mist from the gas fraction.

There are two more methods for the production of an orthophosphorus compound:

Extraction method, which is economical. Its basis is the decomposition of natural phosphate minerals with hydrochloric acid.
Under laboratory conditions, the substance is obtained by the interaction of white phosphorus, which is poisonous with dilute nitric acid. The process requires strict adherence to safety regulations.

Chemical properties

The inorganic compound is considered tribasic, having an average strength. The following chemical properties of phosphoric acid are characteristic:

reacts to indicators by changing color to red;
when heated, it is converted to pyrophosphoric acid;
in aqueous solutions it undergoes a three-stage dissociation;
when reacting with strong acids, it forms phosphoryls - complex salts;
forms a yellow precipitate, interacting with silver nitrate;
thermally decomposes to diphosphoric acid;
on contact with bases, amorphous hydroxides, forms water and salt.

Application

Orthophosphoric acid is used in many areas, from industry to dentistry. The tool is used by craftsmen as a flux when soldering, to clean the surface of the metal from rust. Fluid applied:

for scientific research in molecular biology;
as a catalyst for organic synthesis processes;
for creation of anticorrosive coverings of metals;
in the production of refractory impregnations for wood.

The substance is used:

in the oil industry;
in the manufacture of matches;
for film production;
in order to protect against corrosion;
for clarification of sucrose;
in the manufacture of medicines;
in refrigeration units as a binder in the composition of freon;
during mechanical processing for polishing, cleaning metals;
in the textile industry in the production of fabrics with flame retardant impregnation;
as a component in the production of chemical reagents;
in veterinary medicine for the treatment of urolithiasis in minks;
as a component for a primer on metal.

In the food industry

The use of phosphoric acid in the manufacture of food products has become widespread. It is registered in the register of food additives under the code E338. When used in acceptable amounts, the substance is considered safe. The following properties of the drug are useful:

rancidity prevention;
acidity regulation;
extension of the shelf life;
preservation of taste characteristics;
enhancing the action of antioxidants.

Orthophosphoric acid as an acidulant, baking powder, antioxidant is used in bakery, meat and dairy industries. It is used in the production of confectionery, sugar. The substance gives the products a sour, bitter taste. Additive E338 is a part of:

processed cheeses;
muffins;
carbonated drinks - Pepsi-Cola, Sprite;
sausages;
rolls;
milk;
baby food;
marmalade;
cakes.

Studies have shown that the abuse of foods containing phosphorus compounds, especially carbonated drinks, can lead to health problems. It is not excluded:

leaching of calcium from the body, which can provoke the formation of osteoporosis;
violation of the acid-base balance - the additive is able to increase its acidity;
the appearance of diseases of the gastrointestinal tract;
exacerbation of gastritis;
destruction of tooth enamel;
development of caries;
the appearance of vomiting.

In the non-food industry

The use of orthophosphoric acid can be observed in many areas of production. Often this is due to the chemical properties of the product. The drug is used for the manufacture of:

combined, phosphate mineral fertilizers;
activated carbon;
phosphate salts of sodium, ammonium, manganese;
fire retardant paints;
glass, ceramics;
synthetic detergents;
refractory binders;
non-combustible phosphate foam;
hydraulic fluids for the aviation industry.

In medicine

Dentists use orthophosphorus composition to treat the inner surface of the crown. This helps during prosthetics to improve its adhesion to the tooth. The substance is used by pharmacists for the preparation of medicines, dental cement. In medicine, the use of an orthophosphorus compound is associated with the ability to etch tooth enamel. This is necessary when using adhesive materials of the second, third generation for filling. Important points - after etching, the surface must be:

Rinse;
dry.

Rust application

A rust converter based on phosphoric acid creates a protective layer on the surface that protects against corrosion during further use. A feature of the use of the compound is safety for the metal during application. There are several ways to perform rust removal with phosphoric acid, depending on the size of the damage:

etching with immersion in a bath, other container;
repeated application of the composition to the metal with a spray gun, roller;
surface coating with pre-treated mechanical cleaning.

The orthophosphorus compound converts rust into iron phosphates. The composition can be used for washing and cleaning:

rolled metal products;
wells;
pipeline surfaces;
steam generators;
systems of water supply, heating;
coils;
boilers;
water heaters;
heat exchangers;
boilers;
parts of machines and mechanisms.

The interaction of phosphoric acid

The properties of an inorganic substance determine its interaction with other substances and compounds. This is where chemical reactions take place. The orthophosphorus composition interacts with:

salts of weak acids;
hydroxides, entering into a neutralization reaction;
metals to the left of hydrogen in the activity series with the formation of salt and the release of hydrogen;
basic oxides, participating in the exchange reaction;
ammonium hydroxide, creating ammonium hydrogen phosphate;
ammonia to form acid salts.

Acid Safety

The orthophosphorus compound belongs to the class of hazardous substances and requires caution. Work with the composition should be carried out in a special room equipped with supply and exhaust ventilation, away from sources of fire. Lack of personal protective equipment is unacceptable.