Phosphorus fertilizers. Allotropic modifications of phosphorus

Example.

Example.

1 mole of Ca 3 (PO 4) 2 weighs as much as its molar mass. M[Ca 3 (PO 4) 2 ] = 3 · M (Ca) + 2 · M (P) + 8 · M(O) = 3 · 40,078 + 2 · 30,974 + 8 · · 15.999 = 310.174 g/mol.

Mass of 1 mole of Ca 3 (PO 4) 2 or 6.022 · 10 23 molecules of Ca 3 (PO 4) 2 is equal to 310.174 g.

Atomic mass unit (a.m.u.) (another name is carbon unit (cu)). It is equal to 1/12 of the mass of an atom of a light carbon isotope with mass number 12. The atomic mass unit is a constant value equal to 1.6605402 · 10−24 years

1 amu = m at. (C) = ≈ 0.166 · 10 −26 kg.

Units of measurement a.m.u. – grams, kilograms, etc.

Mass of atoms and molecules . m at. , m mol-ly is expressed in very small quantities of the order of 10 −26 kg.

m(N) = 0.167 · 10 −26 kg = 1.0079 · a.e.m.

m(C) = 1.994 · 10 −26 kg = 12.011 · a.e.m.

m (CO 2) = 7.305 · 10 −26 kg = 12.011 · a.e.m. + 2 · 15,999 · a.e.m.

Units for measuring the masses of atoms and molecules: kg, g, amu. etc.

m at = = A r · a.m.; m mol-ly = = M r · a.e.m.

m any number of particles: m (N) = = M · ν.

m at. (C) = = 1,992· 10 −26 kg;

m at. (C) = = 1,994· 10 −26 kg.

Relative atomic mass(A r) shows how many times the average mass of an atom of the natural isotopic composition of an element is greater than 1 a. e.m. The values ​​of A r are given in the periodic system of elements by D.I. Mendeleev. A r can be calculated using the formula A r = . And r is a dimensionless quantity. Subscript letter “r” is the first letter of the English word relative or Latin relativus – relative, comparative; the mass of an atom is compared to 1 amu.

The raw materials for the production of phosphate fertilizers, phosphorus and all phosphorus compounds are apatite and phosphate ores. The composition of both types of raw materials includes the mineral fluorine-apatite Ca 5 (PO 4) 3 F. Apatite ores are of volcanic origin, while phosphorites are marine sediments.

In pre-revolutionary Russia, only thin deposits of low-quality phosphorites were known and developed. Therefore, an event of enormous national economic significance was the discovery of apatite deposits on the Kola Peninsula, in the Khibiny Mountains, in the 1920s. A large processing plant has been built here, which separates the mined rock into a concentrate with a high phosphorus content and impurities - “nepheline tailings”, used to produce aluminum, soda, potash and cement.

Powerful deposits of phosphorites have been discovered in Southern Kazakhstan, in the Kara-Tau mountains.

The cheapest phosphorus fertilizer is finely ground phosphorite - phosphate rock. Phosphorus is contained in it in the form of water-insoluble calcium phosphate. Therefore, phosphorites are not absorbed by all plants and not on all soils. The bulk of mined phosphorus ores are processed by chemical methods into substances available to all plants on any soil. These are water-soluble calcium phosphates: calcium dihydrogen phosphate Ca(H 2 PO 4) 2, which is part of the superphosphate, a mixture of NH 4 H 2 PO 4 and (NH 4) 2 HPO 4 - ammophos, calcium hydrogen phosphate CaHPO 4 (precipitate), poorly soluble in water, but soluble in weak acids, etc. Phosphoric acid is necessary for the production of soluble phosphates. How to obtain it from natural raw materials?

When calcium phosphate reacts with sulfuric acid, almost insoluble calcium sulfate and an aqueous solution of phosphoric acid are formed:

Ca 3 (PO 4) 2 + 3H 2 SO 4 = 2H 3 PO 4 + 3CaSO 4 ↓ + Q

The reaction products are separated by filtration. Substances involved in this reaction are one in a solid state, the other in a liquid state. Therefore, to increase its speed, the raw material is first finely ground and mixed with sulfuric acid during the reaction. The reaction releases heat, due to which part of the water supplied with sulfuric acid evaporates.

Phosphoric acid is produced industrially in other ways. When natural phosphates interact with coal at a temperature of about 1600°C, phosphorus is obtained in a gaseous state:

2Ca 3 (PO 4) 2 + 10C = P 4 + 10CO + 6CaO - Q

This reaction is carried out in electric arc furnaces. Phosphorus is burned and phosphoric acid is obtained by reacting the resulting phosphorus anhydride with water.

This method produces a purer acid than the first. It can also be obtained from low-quality phosphates. Thanks to the electrification of the country, this method has become widely used in recent years.

By acting on crushed natural phosphates with phosphoric acid, a phosphorus fertilizer with a fairly high content of P2O5, the so-called double superphosphate, is obtained:

Ca 3 (PO 4) 2 + 4H 3 PO 4 = 3Ca (H 2 PO 4) 2

By reacting phosphoric acid with ammonia, an even more valuable fertilizer is obtained - ammophos, a complex fertilizer containing nitrogen along with phosphorus.

Double superphosphate, and especially ammophos, are most widely used in our country. Among other fertilizers obtained on the basis of phosphoric acid, we point out the so-called precipitate (translated from Latin as “sediment”). It is obtained by reacting phosphoric acid with limestone:

H 3 PO 4 + CaCO 3 + H 2 O = CaHPO 4 * 2H 2 O + CO 2

Calcium hydrogen phosphate CaHPO 4, unlike dihydrogen phosphate, is poorly soluble in water, but soluble in weak acids, and therefore in acidic soil solutions, and therefore is well absorbed by plants.

Previously, for more than 100 years, the so-called simple superphosphate, which is obtained by the action of sulfuric acid on natural calcium phosphate without separating the phosphoric acid, was used almost exclusively as a phosphorus fertilizer. The result is a mixture of calcium dihydrogen phosphate and calcium sulfate. This is a fertilizer with a low nutrient content - up to 20% P 2 O 5. Now it is still produced at previously built plants, but according to the long-term plan for the development of mineral fertilizer production in our country, no new simple superphosphate plants will be built.

In the production of phosphoric acid (according to one of the methods discussed) and simple superphosphate, large quantities of sulfuric acid are consumed. Methods for producing phosphorus fertilizers that do not require sulfuric acid have been developed and used at factories. For example, by treating phosphate raw materials with nitric acid, a solution containing phosphoric acid and calcium nitrate is obtained. The solution is cooled and the calcium nitrate crystals are separated. By neutralizing the solution with ammonia, ammophos is obtained.

1. What is the content of the fluorapatite mineral in the Khibiny apatitone-feline rock if the concentrate contains 39.4% P 2 O 5 and assuming that the fluorapatite is completely isolated?
2. Why does fine grinding of phosphate rock improve the efficiency of phosphate rock? Why is it advisable to add phosphate rock to the soil before sowing under fall plowing and mix it well with the soil? How to explain that the effect of phosphate rock is observed over several years?
3. Calculate the theoretical content of P 2 O 5 in simple and double superphosphate.
4. Write an equation for the reaction between average phosphate and nitric acid. Calculate how much 50% nitric acid solution is required according to this equation to react with a concentrate containing 39.4% P 2 O 5.

Answer:
B) yellow.

2. Write the equations for the reactions leading to a change in the acidity of the medium (pH) in a solution of sodium orthophosphate.

Solution:
Let's write the equations:
From PO 4 + H 2 O:
PO 4 −3 + H 2 O → NPO 4 2− + OH −
NPO 4 2− + H 2 O → H 2 PO 4− + OH −
H 2 PO 4 − + H 2 O → H 3 PO 4 + OH −
Consequently, the environment becomes alkaline.

3T. Calcium phosphide formula A) Ca 3 (PO 4) 2 B) Ca (PO 3) 2 C) Ca 2 P 2 O 7 D) Ca 3 P 2

Answer:
D) Ca 3 R 2.
Ca 3 (PO 4) 2 - calcium phosphate;
Ca(PO 3) 2 - calcium phosphite;
Ca 2 P 2 O 7 - calcium pyrophosphate.

4. At what temperature (above or below 100 °C) does the transformation of orthophosphoric acid into diphosphoric acid occur?

Answer:
Conversion of orthophosphoric acid to diphosphoric acid
occurs at T = 200°C.

5. Is the reaction of the formation of diphosphoric acid from orthophosphoric acid exo- or endothermic?

Answer:
The reaction of formation of diphosphoric acid from orthophosphorus
fornoy is exothermic.

6. Draw the structural formula of dichromic acid.

Answer:

The structural formula of dichromic acid H2Cr2O7 has

Simple superphosphate Ca(H2PO4)2·H2O + 2CaSO4. Powdered (PC) contains 19-20% P2O5, granular (RSG) - 19.5-22%. This is the first artificial mineral fertilizer, which began to be produced in 1843 in England, decomposing phosphorites with sulfuric acid.

In Russia, the following is currently obtained by treating apatite concentrate with sulfuric acid:

[Ca3(PO4)2]3 CaF2 + 7H2SO4 + 3H2O → 3Ca(H2PO4)2 H2O + 7CaSO4 + 2HF.

Thus, the fertilizer contains about 40% gypsum. Powdered superphosphate is a white or light gray fine powder with a characteristic odor of phosphoric acid. It dissolves poorly in water.

Due to uneven mixing in the reacting mass, other reactions occur. With a lack of acid, dibasic calcium phosphate is formed:

[Ca3(PO4)2]3 CaF2 + 4H2SO4 + 12H2O → 6CaHPO4 2H2O + 4CaSO4 + 2HF.

As a result, 10-25% of phosphorus is in citrate-soluble form.

When there is an excess of sulfuric acid, phosphoric acid is formed:

[Ca3(PO4)2]3 CaF2 + 10H2SO4 → 6H3PO4 + 10CaSO4 + 2HF.

Therefore, powdered superphosphate contains 5.0-5.5% free phosphoric acid, which determines the high acidity and significant hygroscopicity of the fertilizer. Accordingly, it can become damp and cake. According to the standard, its humidity should not exceed 12-15%.

Granular simple superphosphate– these are light gray irregularly shaped granules measuring 1-4 mm. During granulation, it is dried to a moisture content of 1-4%, phosphoric acid is neutralized with lime-containing materials (limestone, etc.) or phosphorite, its content is reduced to 1.0-2.5%. Therefore, the physical properties of granulated superphosphate are better, it is non-hygroscopic, and practically does not caking.

Double (triple) superphosphate Ca(H2PO4)2 H2O (RSD) contains 43-49% P2O5 (C 76). This is the most concentrated phosphorus fertilizer. Available in granular form. The production technology includes two stages: 1) production of orthophosphoric acid; 2) treatment of apatite with acid (C 80).

Orthophosphoric acid is most often obtained by the extractive method, that is, the decomposition of apatites or phosphorites, including low-percentage ones, with sulfuric acid in accordance with the latter reaction (C 79, 81).

A method has also been developed for producing phosphoric acid through the following technological processes: a) sublimation of phosphorus from low-percentage phosphorites at 1400-1500 ºC, b) combustion of released phosphorus, c) interaction of the resulting phosphorus oxide with water (C 81).

The apatite concentrate is treated with the resulting phosphoric acid:

[Ca3(PO4)2]3 CaF2 + 14H3PO4 + 10H2O→ 10Ca(H2PO4)2 H2O + 2HF.

These are light gray or dark gray granules, slightly soluble in water, 1-4 mm in size. The content of free phosphoric acid does not exceed 2.5%, therefore double superphosphate is non-hygroscopic and does not caking.

Enriched superphosphate contains 23.5-24.5% P2O5. It is obtained by decomposing apatite concentrate with a mixture of sulfuric and phosphoric acids. Available in granular form.

Superfos contains 38-40% P2O5. The production of this fertilizer is based on the interaction of a mixture of sulfuric and phosphoric acids with phosphate rock. Superfos is available in granular form. Water-soluble phosphorus accounts for only half of the total content (19-20%).

When superphosphates are added to the soil, chemical, metabolic and biological absorption of phosphorus occurs, so it is fixed at the site of application and practically does not move along the soil profile. At the same time, chemisorption greatly reduces the availability of phosphorus for plants.

Superphosphates can be used on all soils for all crops. It is more advisable to use simple superphosphate on soils poorly supplied with sulfur, as well as for legumes and cruciferous plants that are more demanding of sulfur.

As the main fertilizer, superphosphates are best applied in the fall for plowing, but can also be applied in the spring for cultivation. To reduce the retrogradation of phosphorus, local (most often, tape) main application of superphosphates is recommended, which determines their slower interaction with the soil.

One of the recommended ways to use granular forms of superphosphates is pre-sowing application. Sometimes they are also used for fertilizing. Powdered superphosphate can be used for sowing and fertilizing only if it has good physical properties, because damp and caked fertilizer clogs the fertilizer sowing apparatus of seeders and plant-feeding cultivators.

Semi-soluble fertilizers (soluble in weak acids)

Precipitate CaHPO4 2H2O(RP) contains 25-35% P2O5. Obtained by neutralizing solutions of phosphoric acid (waste from the production of gelatin from bones) with milk of lime or a suspension of chalk:

H3PO4 + Ca(OH)2 → CaHPO4 2H2O↓;

H3PO4 + CaCO3 + H2O → CaHPO4 2H2O↓ + CO2.

White or light gray finely ground dusting powder, insoluble in water. Accordingly, it is non-hygroscopic and does not caking.

Thomas slag Ca3(PO4)2 CaO contains 8-20% P2O5, but according to the standard, the fertilizer used must contain at least 14% citrate-soluble phosphorus. The fertilizer contains magnesium, iron and microelements (manganese, molybdenum, etc.). This is a waste product from the metallurgical industry, obtained by processing phosphorus-rich cast iron using the Thomas method. Heavy fine powder of dark gray or black color, insoluble in water.

Open-hearth phosphate slag Ca3(PO4)2 CaO (RFS) contains 8-12% P2O5, but the standard requires the content of citrate-soluble phosphorus in the fertilizer to be at least 10% (C 92). Includes iron, magnesium and trace elements. Waste from processing phosphorus-rich cast iron using the open-hearth method. Fine dark gray dusty powder. Does not dissolve in water.

Sparingly soluble fertilizers. Phosphorite flour (phosphorite)(RF) mainly contains phosphorus in the form of fluorapatite [Ca3(PO4)2]3·CaF2; in a simplified form, its chemical formula looks like Ca3(PO4)2. It is obtained by grinding phosphorites to a powder state so that at least 80% of the product passes through a sieve with a hole diameter of 0.17 mm. This is the cheapest phosphorus fertilizer. That is why phosphate rock, despite all its shortcomings, is firmly entrenched in the range of used phosphate fertilizers.

Depending on the deposit of phosphorites, the phosphorus content in phosphate varies greatly. The highest grade contains at least 30% P2O5, the first - 25, the second - 22, the third - 19% P2O5. This is a finely ground dusty powder of gray, earthy gray, dark gray or brown color, insoluble in water.

The rate of decomposition of phosphate rock depends on the degree of acidity of the soil, the type of phosphate rock and the fineness of grinding (C 98).

On soils with a hydrolytic acidity of less than 2.5 meq per 100 g, phosphamide is practically insoluble, and phosphorus from it is not absorbed by plants. Therefore, it is recommended to use it on more acidic soils. In this case, it is also necessary to take into account the value of CEC, since at the same Hg the effect of phosmuca increases with a decrease in absorption capacity.

It is important that phosmuca can act on a par with superphosphate if Hg is higher than the calculated value obtained by the formula:

Ng, meq/100 g of soil = 3 + 0.1ECO (C 99).

The dependence of the action of phosphate rock on the two considered indicators is clearly shown on the graph of Boris Aleksandrovich Golubev (C 100). Thus, good returns from phosphate rock can be expected when used on acidic soddy-podzolic, gray forest, peat soils and red soils, as well as on those with high Hg podzolized and leached chernozems. But when using phosmuca on strongly acidic soils, one should take into account the possibility of retrogradation of water-soluble phosphorus compounds formed during its decomposition.

For the production of phosphate, it is more expedient to use nodular phosphorites that are younger from a geological point of view, which do not have a well-defined crystalline structure and are easier to decompose. Phosphorites of more ancient origin have a crystalline structure, so their phosphorus is much less available to plants.

The effect of phosphate rock, especially on slightly acidic soils, largely depends on the fineness of grinding. The smaller the particle size, the faster the interaction of the fertilizer with the soil and the transition of phosphorus into more soluble compounds occurs (C 101, 102).

Phosphate flour on acidic soils can be applied to all crops, and on neutral soils only to those capable of using phosphorus from tribasic phosphates (lupine, buckwheat, mustard, etc.). When applying phosmuca to neutral soils under other crops, the following methods can be used to decompose phosmuca (C 103).

1) Composting with peat and manure. Peat in most cases has an acidic reaction, which promotes the dissolution of phosphate. In addition, during the decomposition of manure and peat, a significant amount of organic acids (C 104) is released.

2) Applying phosphate rock to the clover grove. After harvesting clover 2 g.p. There remains a lot of stubble and root residues. Phosmuca is distributed over the surface, disking is carried out, and after a week plowing is carried out. Within a week, the turf decomposes under aerobic conditions with the formation of organic acids.

3) Adding phosphate rock to clean steam, in which, as a rule, intensive accumulation of nitrates (nitric acid) occurs.

4) Mixing phosphate with physiologically acidic fertilizers.

Phosphorite flour is used only for the main application, which, to achieve good mixing and long-term interaction with the soil, is best done in the fall under fall plowing.

Phosphorite flour is also used to improve soil fertility, namely, to increase the content of available phosphorus. In this case, high doses of phosphamide are used (1-3 t/ha), which are set depending on the acidity of the soil and the initial content of available phosphorus. This most important reclamation technique, which provides plants with phosphorus for 6-8 years, is called “phosphoritation.”

Phosphorus utilization rates from fertilizers. Phosphorus from water-soluble fertilizers is fixed in large quantities by soils, so in the year of application, plants use only 15-25% of the total amount. Local application of fertilizers increases the phosphorus utilization rate by 1.5-2 times (C 108).

At the same time, phosphorus fertilizers are characterized by a significant aftereffect, that is, they have a positive effect on crop yields for a number of years. During a 7-8-field crop rotation, 40-50% of phosphorus mineral fertilizers are used.

Doses of phosphate fertilizers.

Phosphorus fertilizers are usually applied before sowing and when sowing (planting) crops. In the non-chernozem zone, an average of 30-90 kg/ha of P2O5 is used for the main application for grain crops, and 60-120 kg/ha for row crops and vegetables. When sowing, phosphorus is applied in low doses - from 7 to 30 kg/ha P2O5.

Timing and methods of applying phosphorus fertilizers. It is better to carry out the main application in the fall during autumn plowing, so that the fertilizers reach a deeper layer of soil with relatively stable moisture conditions, ensuring uninterrupted nutrition of the plants. It can also be applied in the spring for cultivation, but shallow application can lead to the fact that fertilizers end up in the upper, often drying out layer of soil.

Phosphorus fertilizers can be added as reserves for 2-3 years. A single application of doses increased by 2-3 times provides plants with phosphorus for 2-3 years, while at the same time reducing the cost of using fertilizers.

A universally recommended method of using superphosphates, especially relevant in case of their deficiency, is pre-sowing application, which is preferably carried out using combined seeders that ensure the placement of fertilizers at a distance of 2.5-3 cm from the seeds in depth or to the side. Granulated superphosphate can be applied along with the seeds, but in order to avoid a decrease in their germination when in contact with fertilizer, the mixture must be prepared immediately before sowing.

For fertilizing, as well as for pre-sowing application, only water-soluble fertilizers are suitable. One-sided phosphorus fertilizing is used very rarely, as a rule, if it was not possible to add a sufficient amount of phosphorus before sowing crops. Therefore, the use of superphosphates for fertilizing is not widespread. An example of adding superphosphate to fertilizing is phosphorus-potassium (mixed with potassium fertilizers) fertilizing of perennial leguminous grasses. It should be noted that this fertilizing is only advisable when using low doses of phosphorus for the grass cover crop.

Basically, nitrogen-phosphorus and nitrogen-phosphorus-potassium fertilizing of row crops is carried out, usually with complex fertilizers.

Superphosphate– this mixture of calcium salts is obtained by treating phosphorites or apatites with a calculated amount of technical sulfuric acid.

Ca 3 (PO 4) 2 + 2H 2 SO 4 = Ca (H 2 PO 4) 2 + 2CaSO 4(P 2 O 5 "20%)

The useful part of superphosphate is water-soluble calcium dihydrogen phosphate, which is well absorbed by plants. Calcium sulfate is a ballast. Therefore, it is more profitable to obtain double superphosphate.

To do this, we first obtain phosphoric acid

Ca 3 (PO 4) 2 + 3H 2 SO 4 = 3CaSO 4 ↓ + 2H 3 PO 4

and then fertilizers

Ca 3 (PO 4) 2 + 4H 3 PO 4 = 3Ca(H 2 PO 4) 2- concentrated phosphorus fertilizer.

In addition to superphosphate, a good phosphorus fertilizer for acidic soils is precipitate. It is obtained by neutralizing phosphoric acid with lime.

H 3 PO 4 + Ca(OH) 2 = CaHPO 4 ↓ + 2H 2 O

Calcium hydrogen phosphate is insoluble in water, but soluble in soil acids.

Ammophos – combined fertilizer, includes nitrogen and phosphorus.

NH 3 + H 3 PO 4 = NH 4 H 2 PO 4

2NH 3 + H 3 PO 4 = (NH 4) 2 HPO 4

1) with R-N connection and 2) without it.

They are less stable with the P-H bond (P-O energy > P-H bond energy), so they are easily oxidized by oxygen.

Phosphorous H 3 P +1 O 2 – monobasic, which does not have anhydride (quite strong K = 8.5 * 10 -2).

Salts - hypophosphites - are highly soluble in H 2 O.

Hypophosphites and H 3 PO 2 are energetic reducing agents (especially in an acidic environment).

Orthophosphorous H 3 +3 PO 3 – H 2 – dibasic, is formed by the interaction of P 4 O 6 with cold H 2 O. This is a crystalline substance, an acid of medium strength K = 8·10 -3.

When heated, H 3 PO 3 disproportionates.

4H 3 RO 3 ® 3H 3 RO 4 + RN 3

Pyrophosphorous - H 4 R 2 O 5.

Phosphoric acid H 4 P 2 O 6– tetrabasic, medium strength (K = 6.1·10-3), its anhydride is not known.

The compound P 2 O 4 is known, but when interacting with H 2 O it gives H 3 PO 3 and H 3 PO 4, i.e. disproportionates like N 2 O 4

Phosphorus phosphorus H 4 P 2 O 6- tribasic has the same composition as phosphorous, but differs in structure.

Biogenic role

Nitrogen in living matter 3·10%, i.e. We live in a nitrogen atmosphere, moderately enriched with oxygen and in very small quantities with other elements.

The term nitrogen means lifeless. It received this name for its inertness to reactions with other elements. At the same time, it is known that without nitrogen it is difficult to imagine life on earth and that nitrogen and life are inseparable concepts.

In the biosphere, nitrogen is formed during bacterial fermentation of protein substances, as well as as a result of the decomposition of nitrogen-containing substances that make up rocks.

It is characteristic that plants and animals consume not free, but bound nitrogen, found in the soil in the form of nitrate and ammonium salts.

The functions of converting free nitrogen into bound nitrogen are performed by nitrogen-fixing bacteria, which, absorbing air nitrogen, use it for the synthesis of proteins and other organic compounds.

Nitrogen compounds, especially nitrates, pollute the biosphere, are harmful to the body and can cause human poisoning. Nitrogen in the soil is in the form of organic substances inaccessible to plants, which are decomposed by bacteria into simple compounds NH 3, CO 2, H 2 O, and salts. The process of releasing ammonia is called ammoniation. Ammonia and soil acids form salts that are absorbed by plants.

Atmospheric nitrogen is fixed by nodule bacteria living on the roots of leguminous plants. These bacteria assimilate nitrogen from the air and create nitrogen substances from it, which are used by plants for the synthesis of proteins.

Phosphorus– belongs to the relatively common elements of the earth’s crust. Clark his 8·10 -2%. Fersman called it the element of life and thought. The body of animals, plants and humans contains phosphorus from hundredths to tenths to whole percent. Its greatest amount is concentrated in bone tissue (in humans, bones contain 5.05%, and tooth enamel contains 17% phosphorus). There is a relatively high amount of phosphorus in brain tissue and muscles. Phosphorus in organisms provides energy processes. With a lack of phosphorus in the body (below 0.1%), animals develop bone diseases.

Arsenic– in different cases and types it acts as a poison and as a healing agent. History provides many cases of arsenic being used as a poison to poison opponents. Symptoms of arsenic poisoning are a metallic taste in the mouth, vomiting, abdominal pain; in severe poisoning, convulsions, paralysis, death.

At the same time, arsenic is ¾ the most important component of many drugs. In small quantities, salts of arsenic and arsenous acids improve animal nutrition and enhance the processes of assimilation and absorption of nitrogen and phosphorus.

NATO countries use arsenic to make deadly weapons.

Orthoarsenates are used in agriculture as insecticides.

Na 2 HAsO 4, Na 3 AsO 4

CaHAsO 4, Ca 3 (AsO 4) 2

LECTURE 6

Topic: p - Elements of group VI