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Sulfuric acid. Concentrated sulfuric acid: properties, reactions Boiling point of sulfuric acid 279.6 c

DEFINITION

anhydrous sulfuric acid is a heavy, viscous liquid that is easily miscible with water in any proportion: the interaction is characterized by an exceptionally large exothermic effect (~880 kJ / mol at infinite dilution) and can lead to explosive boiling and splashing of the mixture if water is added to the acid; that is why it is so important to always use the reverse order in the preparation of solutions and add the acid to the water, slowly and with stirring.

Some physical properties of sulfuric acid are given in the table.

Anhydrous H 2 SO 4 is a remarkable compound with an unusually high dielectric constant and very high electrical conductivity, which is due to the ionic auto-dissociation (autoprotolysis) of the compound, as well as the proton transfer relay conduction mechanism, which ensures the flow of electric current through a viscous liquid with a large number of hydrogen bonds.

Table 1. Physical properties of sulfuric acid.

Getting sulfuric acid

Sulfuric acid is the most important industrial chemical and the cheapest bulk acid produced anywhere in the world.

Concentrated sulfuric acid ("vitriol oil") was first obtained by heating "green vitriol" FeSO 4 ×nH 2 O and spent in large quantities to obtain Na 2 SO 4 and NaCl.

The modern process for producing sulfuric acid uses a catalyst consisting of vanadium(V) oxide with the addition of potassium sulfate on a carrier of silicon dioxide or diatomaceous earth. Sulfur dioxide SO 2 is obtained by burning pure sulfur or by roasting sulfide ore (primarily pyrite or ores of Cu, Ni and Zn) in the process of extracting these metals. Then SO 2 is oxidized to trioxide, and then sulfuric acid is obtained by dissolving in water:

S + O 2 → SO 2 (ΔH 0 - 297 kJ / mol);

SO 2 + ½ O 2 → SO 3 (ΔH 0 - 9.8 kJ / mol);

SO 3 + H 2 O → H 2 SO 4 (ΔH 0 - 130 kJ / mol).

Chemical properties of sulfuric acid

Sulfuric acid is a strong dibasic acid. In the first stage, in solutions of low concentration, it dissociates almost completely:

H 2 SO 4 ↔H + + HSO 4 -.

Dissociation on the second stage

HSO 4 - ↔H + + SO 4 2-

proceeds to a lesser extent. The dissociation constant of sulfuric acid in the second stage, expressed in terms of ion activity, K 2 = 10 -2.

As a dibasic acid, sulfuric acid forms two series of salts: medium and acidic. Medium salts of sulfuric acid are called sulfates, and acid salts are called hydrosulfates.

Sulfuric acid greedily absorbs water vapor and is therefore often used to dry gases. The ability to absorb water also explains the charring of many organic substances, especially those belonging to the class of carbohydrates (fiber, sugar, etc.), when exposed to concentrated sulfuric acid. Sulfuric acid removes hydrogen and oxygen from carbohydrates, which form water, and carbon is released in the form of coal.

Concentrated sulfuric acid, especially hot, is a vigorous oxidizing agent. It oxidizes HI and HBr (but not HCl) to free halogens, coal to CO 2 , sulfur to SO 2 . These reactions are expressed by the equations:

8HI + H 2 SO 4 \u003d 4I 2 + H 2 S + 4H 2 O;

2HBr + H 2 SO 4 \u003d Br 2 + SO 2 + 2H 2 O;

C + 2H 2 SO 4 \u003d CO 2 + 2SO 2 + 2H 2 O;

S + 2H 2 SO 4 \u003d 3SO 2 + 2H 2 O.

The interaction of sulfuric acid with metals proceeds differently depending on its concentration. Dilute sulfuric acid oxidizes with its hydrogen ion. Therefore, it interacts only with those metals that are in the series of voltages only up to hydrogen, for example:

Zn + H 2 SO 4 \u003d ZnSO 4 + H 2.

However, lead does not dissolve in dilute acid because the resulting PbSO 4 salt is insoluble.

Concentrated sulfuric acid is an oxidizing agent due to sulfur (VI). It oxidizes metals in the voltage series up to and including silver. The products of its reduction can be different depending on the activity of the metal and on the conditions (acid concentration, temperature). When interacting with low-active metals, such as copper, the acid is reduced to SO 2:

Cu + 2H 2 SO 4 \u003d CuSO 4 + SO 2 + 2H 2 O.

When interacting with more active metals, reduction products can be both dioxide and free sulfur and hydrogen sulfide. For example, when interacting with zinc, reactions can occur:

Zn + 2H 2 SO 4 \u003d ZnSO 4 + SO 2 + 2H 2 O;

3Zn + 4H 2 SO 4 = 3ZnSO 4 + S↓ + 4H 2 O;

4Zn + 5H 2 SO 4 \u003d 4ZnSO 4 + H 2 S + 4H 2 O.

The use of sulfuric acid

The use of sulfuric acid varies from country to country and from decade to decade. So, for example, in the USA, the main area of H 2 SO 4 consumption is fertilizer production (70%), followed by chemical production, metallurgy, oil refining (~5% in each area). In the UK, the distribution of consumption by industry is different: only 30% of H 2 SO 4 produced is used in the production of fertilizers, but 18% goes to paints, pigments and dye intermediates, 16% to chemical production, 12% to soap and detergents, 10 % for the production of natural and artificial fibers and 2.5% is used in metallurgy.

Examples of problem solving

EXAMPLE 1

Exercise

Determine the mass of sulfuric acid that can be obtained from one ton of pyrite if the yield of sulfur oxide (IV) in the roasting reaction is 90%, and sulfur oxide (VI) in the catalytic oxidation of sulfur (IV) is 95% of the theoretical.

Solution

Let us write the reaction equation for pyrite firing:

4FeS 2 + 11O 2 \u003d 2Fe 2 O 3 + 8SO 2.

Calculate the amount of pyrite substance:

n(FeS 2) = m(FeS 2) / M(FeS 2);

M (FeS 2) \u003d Ar (Fe) + 2 × Ar (S) \u003d 56 + 2 × 32 \u003d 120 g / mol;

n (FeS 2) \u003d 1000 kg / 120 \u003d 8.33 kmol.

Since in the reaction equation the coefficient for sulfur dioxide is twice as large as the coefficient for FeS 2, the theoretically possible amount of sulfur oxide (IV) substance is:

n (SO 2) theor \u003d 2 × n (FeS 2) \u003d 2 × 8.33 \u003d 16.66 kmol.

And practically the amount of mole of sulfur oxide (IV) obtained is:

n (SO 2) pract \u003d η × n (SO 2) theor \u003d 0.9 × 16.66 \u003d 15 kmol.

Let's write the reaction equation for the oxidation of sulfur oxide (IV) to sulfur oxide (VI):

2SO 2 + O 2 \u003d 2SO 3.

The theoretically possible amount of sulfur oxide substance (VI) is:

n(SO 3) theor \u003d n (SO 2) pract \u003d 15 kmol.

And practically the amount of mole of sulfur oxide (VI) obtained is:

n(SO 3) pract = η × n(SO 3) theor = 0.5 × 15 = 14.25 kmol.

We write the reaction equation for the production of sulfuric acid:

SO 3 + H 2 O \u003d H 2 SO 4.

Find the amount of sulfuric acid substance:

n (H 2 SO 4) \u003d n (SO 3) pract \u003d 14.25 kmol.

The reaction yield is 100%. The mass of sulfuric acid is:

m (H 2 SO 4) \u003d n (H 2 SO 4) × M (H 2 SO 4);

M(H 2 SO 4) \u003d 2 × Ar (H) + Ar (S) + 4 × Ar (O) \u003d 2 × 1 + 32 + 4 × 16 \u003d 98 g / mol;

m (H 2 SO 4) \u003d 14.25 × 98 \u003d 1397 kg.

Answer

The mass of sulfuric acid is 1397 kg

Physical properties

Pure 100% sulfuric acid (monohydrate) is a colorless oily liquid that solidifies into a crystalline mass at +10 °C. Reactive sulfuric acid usually has a density of 1.84 g/cm 3 and contains about 95% H 2 SO 4 . It hardens only below -20 °C.

The melting point of the monohydrate is 10.37 °C with a heat of fusion of 10.5 kJ/mol. Under normal conditions, it is a very viscous liquid with a very high dielectric constant (e = 100 at 25 °C). Insignificant own electrolytic dissociation of the monohydrate proceeds in parallel in two directions: [Н 3 SO 4 + ]·[НSO 4 - ] = 2 10 -4 and [Н 3 О + ]·[НS 2 О 7 - ] = 4 10 - 5 . Its molecular-ionic composition can be approximately characterized by the following data (in %):

H 2 SO 4 HSO 4 - H 3 SO 4 + H 3 O + HS 2 O 7 - H 2 S 2 O 7

99,50,180,140,090,050,04

When even small amounts of water are added, dissociation becomes predominant according to the scheme: H 2 O + H 2 SO 4<==>H 3 O + + HSO 4 -

Chemical properties

H 2 SO 4 is a strong dibasic acid.

H2SO4<-->H + + HSO 4 -<-->2H + + SO 4 2-

The first stage (for medium concentrations) leads to 100% dissociation:

K2 = ( ) / = 1.2 10-2

1) Interaction with metals:

a) dilute sulfuric acid dissolves only metals that are in the voltage series to the left of hydrogen:

Zn 0 + H 2 +1 SO 4 (razb) --> Zn +2 SO 4 + H 2 O

b) concentrated H 2 +6 SO 4 - a strong oxidizing agent; when interacting with metals (except Au, Pt), it can be reduced to S +4 O 2, S 0 or H 2 S -2 (Fe, Al, Cr also do not react without heating - they are passivated):

2Ag 0 + 2H 2 +6 SO 4 --> Ag 2 +1 SO 4 + S +4 O 2 + 2H 2 O
8Na 0 + 5H 2 +6 SO 4 --> 4Na 2 +1 SO 4 + H 2 S -2 + 4H 2 O
2) concentrated H 2 S +6 O 4 reacts when heated with some non-metals due to its strong oxidizing properties, turning into sulfur compounds of a lower oxidation state (for example, S + 4 O 2):

C 0 + 2H 2 S +6 O 4 (conc) --> C +4 O 2 + 2S +4 O 2 + 2H 2 O

S 0 + 2H 2 S +6 O 4 (conc) --> 3S +4 O 2 + 2H 2 O

2P 0 + 5H 2 S +6 O 4 (conc) --> 5S +4 O 2 + 2H 3 P +5 O 4 + 2H 2 O
3) with basic oxides:

CuO + H2SO4 --> CuSO4 + H2O

CuO + 2H + --> Cu 2+ + H 2 O

4) with hydroxides:

H 2 SO 4 + 2NaOH --> Na 2 SO 4 + 2H 2 O

H + + OH - --> H 2 O

H 2 SO 4 + Cu(OH) 2 --> CuSO 4 + 2H 2 O

2H + + Cu(OH) 2 --> Cu 2+ + 2H 2 O
5) exchange reactions with salts:

BaCl 2 + H 2 SO 4 --> BaSO 4 + 2HCl

Ba 2+ + SO 4 2- --> BaSO 4

The formation of a white precipitate of BaSO 4 (insoluble in acids) is used to identify sulfuric acid and soluble sulfates.

MgCO 3 + H 2 SO 4 --> MgSO 4 + H 2 O + CO 2 H 2 CO 3

The monohydrate (pure, 100% sulfuric acid) is an ionizing solvent having an acidic character. Sulfates of many metals dissolve well in it (turning into bisulfates), while salts of other acids dissolve, as a rule, only if they can be solvolyzed (with conversion to bisulfates). Nitric acid behaves in monohydrate as a weak base HNO 3 + 2 H 2 SO 4<==>H 3 O + + NO 2 + + 2 HSO 4 - perchloric - as a very weak acid Cl > HClO 4). The monohydrate dissolves well many organic substances containing atoms with unshared electron pairs (capable of attaching a proton). Some of these can then be isolated back unchanged by simply diluting the solution with water. The monohydrate has a high cryoscopic constant (6.12°) and is sometimes used as a medium for determining molecular weights.

Concentrated H 2 SO 4 is a fairly strong oxidizing agent, especially when heated (it is usually reduced to SO 2). For example, it oxidizes HI and partially HBr (but not HCl) to free halogens. It also oxidizes many metals - Cu, Hg, etc. (whereas gold and platinum are stable with respect to H 2 SO 4). So the interaction with copper goes according to the equation:

Cu + 2 H 2 SO 4 \u003d CuSO 4 + SO 2 + H 2 O

Acting as an oxidizing agent, sulfuric acid is usually reduced to SO 2 . However, it can be reduced to S and even H 2 S with the strongest reducing agents. Concentrated sulfuric acid reacts with hydrogen sulfide according to the equation:

H 2 SO 4 + H 2 S \u003d 2H 2 O + SO 2 + S

It should be noted that it is also partially reduced by gaseous hydrogen and therefore cannot be used to dry it.

Rice. 13.

The dissolution of concentrated sulfuric acid in water is accompanied by a significant release of heat (and some decrease in the total volume of the system). Monohydrate almost does not conduct electricity. In contrast, aqueous solutions of sulfuric acid are good conductors. As seen in fig. 13, approximately 30% acid has the maximum electrical conductivity. The minimum of the curve corresponds to a hydrate with the composition H 2 SO 4 ·H 2 O.

The release of heat upon dissolution of the monohydrate in water is (depending on the final concentration of the solution) up to 84 kJ/mol H 2 SO 4 . On the contrary, by mixing 66% sulfuric acid, pre-cooled to 0 ° C, with snow (1: 1 by weight), a decrease in temperature can be achieved, down to -37 ° C.

The change in the density of aqueous solutions of H 2 SO 4 with its concentration (wt.%) is given below:

As can be seen from these data, the determination of the density of the concentration of sulfuric acid above 90 wt. % becomes quite inaccurate. Water vapor pressure over H 2 SO 4 solutions of different concentrations at different temperatures is shown in fig. 15. Sulfuric acid can act as a drying agent only as long as the water vapor pressure over its solution is less than its partial pressure in the gas being dried.

Rice. 15.

Rice. 16. Boiling points over H 2 SO 4 solutions. H 2 SO 4 solutions.

When a dilute solution of sulfuric acid is boiled, water is distilled off from it, and the boiling point rises up to 337 ° C, when 98.3% H 2 SO 4 begins to distill (Fig. 16). On the contrary, excess sulfuric anhydride volatilizes from more concentrated solutions. The steam of sulfuric acid boiling at 337 ° C is partially dissociated into H 2 O and SO 3, which recombine upon cooling. The high boiling point of sulfuric acid allows it to be used to isolate volatile acids from their salts (for example, HCl from NaCl) when heated.

Receipt

The monohydrate can be obtained by crystallization of concentrated sulfuric acid at -10°C.

Sulfuric acid production.

1st stage. Pyrite kiln.
4FeS 2 + 11O 2 --> 2Fe 2 O 3 + 8SO 2 + Q

The process is heterogeneous:

1) grinding iron pyrite (pyrite)
2) "fluidized bed" method
3) 800°С; removal of excess heat
4) increase in the concentration of oxygen in the air
2nd stage. After cleaning, drying and heat exchange, sulfur dioxide enters the contact apparatus, where it is oxidized to sulfuric anhydride (450 ° C - 500 ° C; catalyst V 2 O 5):
2SO2 + O2
3rd stage. Absorption tower:

nSO 3 + H 2 SO 4 (conc) --> (H 2 SO 4 nSO 3) (oleum)

Water cannot be used due to the formation of fog. Apply ceramic nozzles and the principle of counterflow.

Application.

Remember! Sulfuric acid must be poured into water in small portions, and not vice versa. Otherwise, a violent chemical reaction may occur, as a result of which a person may receive severe burns.

Sulfuric acid is one of the main products of the chemical industry. It goes to the production of mineral fertilizers (superphosphate, ammonium sulfate), various acids and salts, medicines and detergents, dyes, artificial fibers, explosives. It is used in metallurgy (decomposition of ores, for example, uranium), for the purification of petroleum products, as a desiccant, etc.

Practically important is the fact that very strong (above 75%) sulfuric acid does not act on iron. This allows you to store and transport it in steel tanks. On the contrary, dilute H 2 SO 4 easily dissolves iron with the release of hydrogen. Oxidizing properties are not typical for it at all.

Strong sulfuric acid absorbs moisture vigorously and is therefore often used to dry gases. From many organic substances containing hydrogen and oxygen, it takes away water, which is often used in technology. With the same (as well as with the oxidizing properties of strong H 2 SO 4) its destructive effect on plant and animal tissues is associated. Sulfuric acid that accidentally gets on the skin or dress during work should be immediately washed off with plenty of water, then moisten the affected area with a dilute ammonia solution and rinse again with water.

Sulfuric acid H 2 SO 4 , molar mass 98.082; colorless oily, odorless. Very strong diacid, at 18°C p K a 1 - 2.8, K 2 1.2 10 -2, pK a 2 1.92; bond lengths in S=O 0.143 nm, S-OH 0.154 nm, angle HOSOH 104°, OSO 119°; boils with decomposition, forming (98.3% H 2 SO 4 and 1.7% H 2 O with a boiling point of 338.8 ° C; see also table. 1). Sulfuric acid, corresponding to 100% H 2 SO 4 content, has a composition (%): H 2 SO 4 99.5%, HSO 4 - 0.18%, H 3 SO 4 + 0.14%, H 3 O + 0 09%, H 2 S 2 O 7 0.04%, HS 2 O 7 0.05%. Miscible with and SO 3 in all proportions. In aqueous solutions sulfuric acid almost completely dissociates into H + , HSO 4 - and SO 4 2- . Forms H 2 SO 4 · n H 2 O, where n=1, 2, 3, 4 and 6.5.

solutions of SO 3 in sulfuric acid are called oleum, they form two compounds H 2 SO 4 SO 3 and H 2 SO 4 2SO 3. Oleum also contains pyrosulfuric acid, which is obtained by the reaction: H 2 SO 4 +SO 3 =H 2 S 2 O 7 .

Getting sulfuric acid

Raw material for receiving sulfuric acid serve as: S, metal sulfides, H 2 S, waste from thermal power plants, Fe, Ca sulfates, etc. The main stages of production sulfuric acid: 1) raw materials to obtain SO 2 ; 2) SO 2 to SO 3 (conversion); 3) SO3. In industry, two methods are used to obtain sulfuric acid, differing in the way of oxidation of SO 2 - contact using solid catalysts (contacts) and nitrous - with nitrogen oxides. For getting sulfuric acid In the contact method, modern plants use vanadium catalysts that have displaced Pt and Fe oxides. Pure V 2 O 5 has a weak catalytic activity, which sharply increases in the presence of alkali metals, with K salts having the greatest effect. 7 V 2 O 5 and K 2 S 2 O 7 V 2 O 5 decomposing at 315-330, 365-380 and 400-405 °C, respectively). The active component under catalysis is in a molten state.

The scheme for the oxidation of SO 2 to SO 3 can be represented as follows:

At the first stage, equilibrium is reached, the second stage is slow and determines the speed of the process.

Production sulfuric acid from sulfur by the method of double contact and double absorption (Fig. 1) consists of the following stages. The air after cleaning from dust is supplied by a gas blower to the drying tower, where it is dried 93-98% sulfuric acid to a moisture content of 0.01% by volume. The dried air enters the sulfur furnace after preheating in one of the heat exchangers of the contact unit. The furnace burns sulfur supplied by nozzles: S + O 2 = SO 2 + 297.028 kJ. The gas containing 10-14% by volume of SO 2 is cooled in the boiler and after dilution with air to the content of SO 2 9-10% by volume at 420°C enters the contact apparatus for the first stage of conversion, which proceeds on three layers of catalyst (SO 2 + V 2 O 2 = SO 3 + 96.296 kJ), after which the gas is cooled in heat exchangers. Then the gas containing 8.5-9.5% SO 3 at 200°C enters the first stage of absorption into the absorber, irrigated and 98% sulfuric acid: SO 3 + H 2 O \u003d H 2 SO 4 + 130.56 kJ. The gas is then spattered. sulfuric acid, heated to 420°C and enters the second stage of the conversion, flowing on two layers of catalyst. Before the second absorption stage, the gas is cooled in the economizer and fed into the second stage absorber, irrigated with 98% sulfuric acid, and then, after cleaning from splashes, it is released into the atmosphere.

1 - sulfur furnace; 2 - waste heat boiler; 3 - economizer; 4 - starting furnace; 5, 6 - heat exchangers of the starting furnace; 7 - contact device; 8 - heat exchangers; 9 - oleum absorber; 10 - drying tower; 11 and 12, respectively, the first and second monohydrate absorbers; 13 - acid collectors.

1 - plate feeder; 2 - oven; 3 - waste heat boiler; 4 - cyclones; 5 - electrostatic precipitators; 6 - washing towers; 7 - wet electrostatic precipitators; 8 - blowing tower; 9 - drying tower; 10 - spray trap; 11 - the first monohydrate absorber; 12 - heat exchangers; 13 - contact device; 14 - oleum absorber; 15 - second monohydrate absorber; 16 - refrigerators; 17 - collections.

1 - denitration tower; 2, 3 - the first and second production towers; 4 - oxidation tower; 5, 6, 7 - absorption towers; 8 - electrostatic precipitators.

Production sulfuric acid from metal sulfides (Fig. 2) is much more complicated and consists of the following operations. Roasting of FeS 2 is carried out in an air-blast fluidized bed furnace: 4FeS 2 + 11O 2 = 2Fe 2 O 3 + 8SO 2 + 13476 kJ. Roasting gas containing SO 2 13-14%, having a temperature of 900°C, enters the boiler, where it is cooled to 450°C. Dust removal is carried out in a cyclone and an electrostatic precipitator. Next, the gas passes through two washing towers, irrigated with 40% and 10% sulfuric acid. At the same time, the gas is finally purified from dust, fluorine and arsenic. For cleaning gas from aerosol sulfuric acid formed in the washing towers, two stages of wet electrostatic precipitators are provided. After drying in a drying tower, before which the gas is diluted to a content of 9% SO 2 , it is fed to the first conversion stage (3 catalyst beds) by a blower. In heat exchangers, the gas is heated to 420°C due to the heat of the gas coming from the first conversion stage. SO 2 , oxidized to 92-95% in SO 3 , goes to the first stage of absorption in oleum and monohydrate absorbers, where it is released from SO 3 . Next, the gas containing SO 2 ~ 0.5% enters the second conversion stage, which takes place on one or two catalyst layers. The gas is preliminarily heated in another group of heat exchangers up to 420 °C due to the heat of the gases coming from the second stage of catalysis. After separation of SO 3 in the second stage of absorption, the gas is released into the atmosphere.

The degree of conversion of SO 2 to SO 3 in the contact method is 99.7%, the degree of absorption of SO 3 is 99.97%. Production sulfuric acid carried out in one stage of catalysis, while the degree of conversion of SO 2 to SO 3 does not exceed 98.5%. Before being released into the atmosphere, the gas is purified from the remaining SO 2 (see). The productivity of modern plants is 1500-3100 tons/day.

The essence of the nitrous method (Fig. 3) is that the roasting gas, after cooling and cleaning from dust, is treated with the so-called nitrose - sulfuric acid in which nitrogen oxides are dissolved. SO 2 is absorbed by nitrose, and then oxidized: SO 2 + N 2 O 3 + H 2 O \u003d H 2 SO 4 + NO. The resulting NO is poorly soluble in nitrose and is released from it, and then partially oxidized by oxygen in the gas phase to NO 2 . A mixture of NO and NO 2 is reabsorbed sulfuric acid etc. Nitrogen oxides are not consumed in the nitrous process and are returned to the production cycle due to incomplete absorption of them. sulfuric acid they are partly carried away by the exhaust gases. Advantages of the nitrous method: simplicity of hardware design, lower cost (10-15% lower than the contact one), the possibility of 100% SO 2 processing.

The instrumentation of the tower nitrous process is simple: SO 2 is processed in 7-8 lined towers with ceramic packing, one of the towers (hollow) is an adjustable oxidizing volume. The towers have acid collectors, refrigerators, pumps that supply acid to pressure tanks above the towers. A tail fan is installed in front of the last two towers. For cleaning gas from aerosol sulfuric acid serves as an electrostatic precipitator. The nitrogen oxides required for the process are obtained from HNO 3 . To reduce the emission of nitrogen oxides into the atmosphere and 100% SO 2 processing, a nitrous-free SO 2 processing cycle is installed between the production and absorption zones in combination with a water-acid method for deep trapping of nitrogen oxides. The disadvantage of the nitrous method is the low quality of the product: concentration sulfuric acid 75%, the presence of nitrogen oxides, Fe and other impurities.

To reduce the possibility of crystallization sulfuric acid during transportation and storage, standards for commercial grades are established sulfuric acid, whose concentration corresponds to the lowest crystallization temperatures. Content sulfuric acid in technical grades (%): tower (nitrous) 75, contact 92.5-98.0, oleum 104.5, high-percentage oleum 114.6, battery 92-94. sulfuric acid stored in steel tanks with a volume of up to 5000 m 3, their total capacity in the warehouse is designed for a ten-day production. Oleum and sulfuric acid transported in steel railway tanks. Concentrated and battery sulfuric acid transported in acid-resistant steel tanks. Tanks for the transportation of oleum are covered with thermal insulation and the oleum is heated before filling.

Determine sulfuric acid colorimetrically and photometrically, in the form of a suspension of BaSO 4 - phototurbidimetrically, as well as by the coulometric method.

The use of sulfuric acid

Sulfuric acid is used in the production of mineral fertilizers, as an electrolyte in lead batteries, for the production of various mineral acids and salts, chemical fibers, dyes, smoke-forming substances and explosives, in the oil, metalworking, textile, leather and other industries. It is used in industrial organic synthesis in dehydration reactions (obtaining diethyl ether, esters), hydration (ethanol from ethylene), sulfonation (and intermediate products in the production of dyes), alkylation (obtaining isooctane, polyethylene glycol, caprolactam), etc. The largest consumer sulfuric acid- production of mineral fertilizers. For 1 ton of P 2 O 5 phosphate fertilizers, 2.2-3.4 tons are consumed sulfuric acid, and for 1 t (NH 4) 2 SO 4 - 0.75 t sulfuric acid. Therefore, sulfuric acid plants tend to be built in conjunction with plants for the production of mineral fertilizers. World production sulfuric acid in 1987 reached 152 million tons.

Sulfuric acid and oleum - extremely aggressive substances that affect the respiratory tract, skin, mucous membranes, cause difficulty in breathing, cough, often - laryngitis, tracheitis, bronchitis, etc. MPC of sulfuric acid aerosol in the air of the working area is 1.0 mg/m 3 , in the atmosphere 0.3 mg/m 3 (maximum one-time) and 0.1 mg/m 3 (daily average). The striking concentration of vapors sulfuric acid 0.008 mg/l (60 min exposure), lethal 0.18 mg/l (60 min). Hazard class 2. Aerosol sulfuric acid can be formed in the atmosphere as a result of emissions from chemical and metallurgical industries containing oxides of S, and fall out as acid rain.

Author Chemical Encyclopedia b.b. N.S.Zefirov

SULFURIC ACID H 2 SO 4 , molecular weight 98.082; colorless odorless oily liquid. Very strong dibasic acid, at 18°C pK a 1 - 2.8, K 2 1.2 10 -2, pK a 2 l.92; bond lengths in the molecule S=O 0.143 nm, S-OH 0.154 nm, angle HOSOH 104°, OSO 119°; boils with various, forming an azeotropic mixture (98.3% H 2 SO 4 and 1.7% H 2 O with a boiling point of 338.8 ° C; see also Table 1). SULFURIC ACID, corresponding to 100% H 2 SO 4 content, has the composition (%): H 2 SO 4 99.5, 0.18, 0.14, H 3 O + 0.09, H 2 S 2 O 7 0.04, HS 2 O 7 0.05. Miscible with water and SO 3 in all proportions. In aqueous solutions, SULFURIC ACID is almost completely dissociated into H + , and . Forms hydrates H 2 SO 4 nH 2 O, where n = 1, 2, 3, 4 and 6.5.

SO 3 solutions in SULFURIC ACID are called oleum, they form two compounds H 2 SO 4 SO 3 and H 2 SO 4 2SO 3. Oleum also contains pyrosulfuric acid, which is obtained by the reaction: H 2 SO 4 + + SO 3: H 2 S 2 O 7.

The boiling point of aqueous solutions of SULFURIC ACID to. increases with an increase in its concentration and reaches a maximum at a content of 98.3% H 2 SO 4 (Table 2). The boiling point of oleum decreases with increasing SO 3 content. With an increase in the concentration of aqueous solutions of SULFURIC ACID, the total vapor pressure over the solutions decreases and, at a content of 98.3% H 2 SO 4, reaches a minimum. With an increase in the concentration of SO 3 in oleum, the total vapor pressure above it increases. The vapor pressure over aqueous solutions of SULFURIC ACID c. and oleum can be calculated by the equation: lgp (Pa) \u003d A - B / T + 2.126, the values \u200b\u200bof the coefficients A and B depend on the concentration of SULFURIC ACID c. Steam over aqueous solutions of SULFURIC ACID c. from a mixture of water vapor, H 2 SO 4 and SO 3, while the composition of the vapor differs from the composition of the liquid at all concentrations of SULFURIC ACID c., except for the corresponding azeotropic mixture.

With increasing temperature, the dissociation of H 2 SO 4 H 2 O + SO 3 - Q increases, the equation for the temperature dependence of the equilibrium constant lnК p = 14.74965 - 6.71464ln (298 / T) - 8, 10161 10 4 T 2 -9643.04 /T-9.4577 10 -3 T+2.19062 x 10 -6 T 2 . At normal pressure, the degree of dissociation: 10 -5 (373 K), 2.5 (473 K), 27.1 (573 K), 69.1 (673 K). The density of 100% SULFURIC ACID can be determined by the equation: d = 1.8517 - - 1.1 10 -3 t + 2 10 -6 t 2 g / cm 3. With an increase in the concentration of SULFURIC ACID solutions, their heat capacity decreases and reaches a minimum for 100% SULFURIC ACID, while the heat capacity of oleum increases with increasing SO 3 content.

With an increase in concentration and a decrease in temperature, the thermal conductivity l decreases: l \u003d 0.518 + 0.0016t - (0.25 + + t / 1293) C / 100, where C is the concentration of SULFURIC ACID c., in%. Max. viscosity has oleum H 2 SO 4 SO 3, with increasing temperature h decreases. Electric resistance of SULFURIC ACID to. is minimal at a concentration of 30 and 92% H 2 SO 4 and maximum at a concentration of 84 and 99.8% H 2 SO 4 . For oleum min. r at a concentration of 10% SO 3 . With an increase in temperature, r SULFURIC ACID increases. Dielectric permeability 100% SULFURIC ACID room 101 (298.15 K), 122 (281.15 K); cryoscopic constant 6.12, ebulioscopic. constant 5.33; vapor diffusion coefficient SULFURIC ACID in air changes with temperature; D \u003d 1.67 10 -5 T 3/2 cm 2 / s.

SULFURIC ACID is a fairly strong oxidizing agent, especially when heated; oxidizes HI and partially HBr to free halogens, carbon to CO 2, S to SO 2, oxidizes many metals (Cu, Hg, etc.). In this case, SULFURIC ACID is reduced to SO 2, and the most powerful reducing agents are reduced to S and H 2 S. Conc. H 2 SO 4 is partially reduced by H 2 , which is why it cannot be used for drying it. Diff. H 2 SO 4 interaction with all metals that are in the electrochemical series of voltages to the left of hydrogen, with the release of H 2 . Oxidize properties for dilute H 2 SO 4 are uncharacteristic. SULFURIC ACID gives two series of salts: medium sulfates and acidic hydrosulfates (see Inorganic sulfates), as well as ethers (see Organic sulfates). Peroxomonosulphuric (Caro's acid) H 2 SO 5 and peroxodisulfuric H 2 S 2 O 8 acids are known (see Sulfur).

Receipt. The raw materials for obtaining SULFURIC ACID are: S, metal sulfides, H 2 S, exhaust gases from thermal power plants, sulfates of Fe, Ca, etc. Main. stages of obtaining SULFURIC ACID k.: 1) roasting of raw materials to obtain SO 2 ; 2) oxidation of SO 2 to SO 3 (conversion); 3) SO 3 absorption. In industry, two methods are used to obtain SULFURIC ACID, which differ in the way SO 2 is oxidized, contact using solid catalysts (contacts) and nitrous, with nitrogen oxides. To obtain SULFURIC ACID by the contact method, modern plants use vanadium catalysts that have displaced Pt and Fe oxides. Pure V 2 O 5 has a weak catalytic activity, which sharply increases in the presence of alkali metal salts, with K salts having the most influence. 7 V 2 O 5 and K 2 S 2 O 7 V 2 O 5 , decomposing at 315-330, 365-380 and 400-405 °C, respectively). The active component under catalysis is in a molten state.

The scheme for the oxidation of SO 2 to SO 3 can be represented as follows:

At the first stage, equilibrium is reached, the second stage is slow and determines the speed of the process.

The production of SULFURIC ACID from sulfur by the method of double contact and double absorption (Fig. 1) consists of the following stages. The air after cleaning from dust is supplied by a gas blower to the drying tower, where it is dried with 93-98% SULFURIC ACID to a moisture content of 0.01% by volume. The dried air enters the sulfur furnace after pre-heating. heating in one of the heat exchangers of the contact unit. The furnace burns sulfur supplied by nozzles: S + O 2 : SO 2 + + 297.028 kJ. The gas containing 10-14% by volume of SO 2 is cooled in the boiler and, after dilution with air to a SO 2 content of 9-10% by volume at 420 ° C, enters the contact apparatus for the first stage of conversion, which proceeds on three layers of catalyst (SO 2 + V 2 O 2 : : SO 3 + 96.296 kJ), after which the gas is cooled in heat exchangers. Then the gas containing 8.5-9.5% SO 3 at 200 ° C enters the first stage of absorption into the absorber, irrigated with oleum and 98% SULFURIC ACID to .: SO 3 + H 2 O: H 2 SO 4 + + 130.56 kJ. Next, the gas is cleaned from splashes of SULFURIC ACID, heated to 420 ° C and enters the second stage of conversion, which takes place on two layers of catalyst. Before the second stage of absorption, the gas is cooled in the economizer and fed into the second stage absorber, irrigated with 98% SULFURIC ACID, and then, after cleaning from splashes, it is released into the atmosphere.

Rice. 1. Scheme for the production of sulfuric acid from sulfur: 1-sulfuric furnace; 2-heat recovery boiler; 3 - economizer; 4-starter firebox; 5, 6-heat exchangers of the starting furnace; 7-pin device; 8-heat exchangers; 9-oleum absorber; 10 drying tower; 11 and 12, respectively, the first and second monohydrate absorbers; 13-collectors of acid.

Fig.2. Scheme for the production of sulfuric acid from pyrite: 1-dish feeder; 2-furnace; 3-heat recovery boiler; 4-cyclones; 5-electrostatic precipitators; 6 washing towers; 7-wet electrostatic precipitators; 8 blow tower; 9-drying tower; 10-splash trap; 11-first monohydrate absorber; 12-heat exchange-wiki; 13 - contact device; 14-oleum absorber; 15 second monohydrate absorber; 16 refrigerators; 17 collections.

Rice. 3. Scheme for the production of sulfuric acid by the nitrous method: 1 - denitratz. tower; 2, 3-first and second products. towers; 4-oxidize. tower; 5, 6, 7-absorpt. towers; 8 - electrostatic precipitators.

The production of SULFURIC ACID from metal sulfides (Fig. 2) is much more complicated and consists of the following operations. Roasting of FeS 2 is carried out in an air-blast fluidized bed furnace: 4FeS 2 + 11O 2: 2Fe 2 O 3 + 8SO 2 + 13476 kJ. Roasting gas with a SO 2 content of 13-14%, having a temperature of 900 °C, enters the boiler, where it is cooled to 450 °C. Dust removal is carried out in a cyclone and an electrostatic precipitator. Further, the gas passes through two washing towers, irrigated with 40% and 10% SULFURIC ACID. At the same time, the gas is finally purified from dust, fluorine and arsenic. Two stages of wet electrostatic precipitators are provided for gas purification from SULFURIC ACID aerosol formed in washing towers. After drying in a drying tower, before which the gas is diluted to a content of 9% SO 2 , it is fed to the first conversion stage (3 catalyst beds) by a blower. In heat exchangers, the gas is heated up to 420 °C due to the heat of the gas coming from the first stage of the conversion. SO 2 , oxidized to 92-95% in SO 3 , goes to the first stage of absorption in oleum and monohydrate absorbers, where it is released from SO 3 . Next, the gas containing SO 2 ~ 0.5% enters the second conversion stage, which takes place on one or two catalyst layers. The gas is preliminarily heated in another group of heat exchangers up to 420 °C due to the heat of the gases coming from the second stage of catalysis. After separation of SO 3 in the second stage of absorption, the gas is released into the atmosphere.

The degree of conversion of SO 2 to SO 3 in the contact method is 99.7%, the degree of absorption of SO 3 is 99.97%. The production of SULFURIC ACID is also carried out in one stage of catalysis, while the degree of conversion of SO 2 to SO 3 does not exceed 98.5%. Before being released into the atmosphere, the gas is purified from the remaining SO 2 (see Gas purification). The productivity of modern installations is 1500-3100 tons / day.

The essence of the nitrous method (Fig. 3) is that the roasting gas, after cooling and cleaning from dust, is treated with the so-called nitrose-C. to., in which sol. nitrogen oxides. SO 2 is absorbed by nitrose, and then oxidized: SO 2 + N 2 O 3 + H 2 O: H 2 SO 4 + NO. The resulting NO is poorly soluble in nitrose and is released from it, and then partially oxidized by oxygen in the gas phase to NO 2 . The mixture of NO and NO 2 is reabsorbed by SULFURIC ACID. etc. Nitrogen oxides are not consumed in the nitrous process and are returned to production. cycle, due to incomplete absorption of their SULFURIC ACID to. they are partially carried away by the exhaust gases. Advantages of the nitrous method: simplicity of hardware design, lower cost (10-15% lower than the contact one), the possibility of 100% SO 2 processing.

The instrumentation of the tower nitrous process is simple: SO 2 is processed in 7-8 lined towers with ceramic. nozzle, one of the towers (hollow) is an adjustable oxidizer. volume. The towers have acid collectors, refrigerators, pumps that supply acid to pressure tanks above the towers. A tail fan is installed in front of the last two towers. An electrostatic precipitator serves to purify the gas from the aerosol of SULFURIC ACID. The nitrogen oxides required for the process are obtained from HNO 3 . To reduce the emission of nitrogen oxides into the atmosphere and 100% SO 2 processing, a nitrous-free SO 2 processing cycle is installed between the production and absorption zones in combination with a water-acid method for deep trapping of nitrogen oxides. The disadvantage of the nitrous method is the low quality of products: the concentration of SULFURIC ACID is 75%, the presence of nitrogen oxides, Fe, and other impurities.

To reduce the possibility of SULFURIC ACID crystallization during transportation and storage, standards have been established for commercial grades of SULFURIC ACID, the concentration of which corresponds to the lowest crystallization temperatures. Content SULFURIC ACID c. in tech. grades (%): tower (nitrous) 75, contact 92.5-98.0, oleum 104.5, high-percentage oleum 114.6, battery 92-94. SULFURIC ACID is stored in steel tanks up to 5000 m 3 in volume, their total capacity in the warehouse is designed for ten days of production. Oleum and SULFURIC ACID are transported in steel railway tanks. Conc. and battery SULFURIC ACID to. are transported in acid-resistant steel tanks. Tanks for the transportation of oleum are covered with thermal insulation and the oleum is heated before filling.

SULFURIC ACID is determined colorimetrically and photometrically, in the form of a suspension of BaSO 4 - phototurbidimetrically, as well as coulometrically. method.

Application. SULFURIC ACID is used in the production of mineral fertilizers, as an electrolyte in lead batteries, for the production of various mineral acids and salts, chemical fibers, dyes, smoke-forming substances and explosives, in the oil, metalworking, textile, leather, and other industries. It is used in prom. organic synthesis in dehydration reactions (obtaining diethyl ether, esters), hydration (ethanol from ethylene), sulfonation (synthetic detergents and intermediate products in the production of dyes), alkylation (obtaining isooctane, polyethylene glycol, capro-lactam), etc. The largest consumer of SULFURIC ACID is the production of mineral fertilizers. For 1 ton of P 2 O 5 phosphate fertilizers, 2.2-3.4 tons of SULFURIC ACID are consumed, and for 1 ton of (NH 4) 2 SO 4 -0.75 tons of SULFURIC ACID. Therefore, sulfuric acid plants tend to be built in a complex with factories for the production of mineral fertilizers. World production of SULFURIC ACID in 1987 reached 152 million tons.

SULFURIC ACID and oleum are extremely aggressive substances that affect the respiratory tract, skin, mucous membranes, cause breathing difficulties, cough, often laryngitis, tracheitis, bronchitis, etc. Aerosol MPC SULFURIC ACID to. in the air of the working area 1, 0 mg / m 3, in atm. air 0.3 mg / m 3 (max. single) and 0.1 mg / m 3 (daily average). The damaging concentration of SULFURIC ACID vapors is 0.008 mg / l (exposure 60 minutes), lethal 0.18 mg / l (60 minutes). Hazard class 2. Aerosol SULFURIC ACID can be formed in the atmosphere as a result of chemical and metallurgical emissions. industries containing S oxides and fall out as acid rain.

Literature: Handbook of sulfuric acid, ed. K. M. Malina, 2nd ed., M., 1971; Amelin A.G., Technology of sulfuric acid, 2nd ed., M., 1983; Vasiliev B.T., Otvagina M.I., Technology of sulfuric acid, M., 1985. Yu.V. Filatov.

Chemical encyclopedia. Volume 4 >>

physical properties.

H2SO4	HSO 4-	H3SO4+	H3O+	HS 2 O 7 -	H2S2O7
99,5	0,18	0,14	0,09	0,05	0,04

When even small amounts of water are added, dissociation becomes predominant according to the scheme:

H 2 O + H 2 SO 4<==>H 3 O + + HSO 4 -

Chemical properties.

H 2 SO 4 is a strong dibasic acid.

H2SO4<-->H + + HSO 4 -<-->2H + + SO 4 2-

The first stage (for medium concentrations) leads to 100% dissociation:

K 2 \u003d ( ) / \u003d 1.2 10 -2

1) Interaction with metals:

a) dilute sulfuric acid dissolves only metals that are in the voltage series to the left of hydrogen:

Zn 0 + H 2 +1 SO 4 (razb) --> Zn +2 SO 4 + H 2 O

2Ag 0 + 2H 2 +6 SO 4 --> Ag 2 +1 SO 4 + S +4 O 2 + 2H 2 O

8Na 0 + 5H 2 +6 SO 4 --> 4Na 2 +1 SO 4 + H 2 S -2 + 4H 2 O

2) concentrated H 2 S +6 O 4 reacts when heated with some non-metals due to its strong oxidizing properties, turning into sulfur compounds of a lower oxidation state, (for example, S + 4 O 2):

C 0 + 2H 2 S +6 O 4 (conc) --> C +4 O 2 + 2S +4 O 2 + 2H 2 O

S 0 + 2H 2 S +6 O 4 (conc) --> 3S +4 O 2 + 2H 2 O

2P 0 + 5H 2 S +6 O 4 (conc) --> 5S +4 O 2 + 2H 3 P +5 O 4 + 2H 2 O

3) with basic oxides:

CuO + H2SO4 --> CuSO4 + H2O

CuO + 2H + --> Cu 2+ + H 2 O

4) with hydroxides:

H 2 SO 4 + 2NaOH --> Na 2 SO 4 + 2H 2 O

H + + OH - --> H 2 O

H 2 SO 4 + Cu(OH) 2 --> CuSO 4 + 2H 2 O

2H + + Cu(OH) 2 --> Cu 2+ + 2H 2 O

5) exchange reactions with salts:

BaCl 2 + H 2 SO 4 --> BaSO 4 + 2HCl

Ba 2+ + SO 4 2- --> BaSO 4

The formation of a white precipitate of BaSO 4 (insoluble in acids) is used to identify sulfuric acid and soluble sulfates.

HNO 3 + 2 H 2 SO 4<==>H 3 O + + NO 2 + + 2 HSO 4 -

perchloric - as a very weak acid

H 2 SO 4 + HClO 4 = H 3 SO 4 + + ClO 4 -

Fluorosulfonic and chlorosulfonic acids are somewhat stronger (HSO 3 F> HSO 3 Cl> HClO 4). The monohydrate dissolves well many organic substances containing atoms with unshared electron pairs (capable of attaching a proton). Some of these can then be isolated back unchanged by simply diluting the solution with water. The monohydrate has a high cryoscopic constant (6.12°) and is sometimes used as a medium for determining molecular weights.

Cu + 2 H 2 SO 4 \u003d CuSO 4 + SO 2 + H 2 O

H 2 SO 4 + H 2 S \u003d 2H 2 O + SO 2 + S

It should be noted that it is also partially reduced by gaseous hydrogen and therefore cannot be used to dry it.

Rice. 13. Electrical conductivity of sulfuric acid solutions.

The change in the density of aqueous solutions of H 2 SO 4 with its concentration (wt.%) is given below:

	5	10	20	30	40	50	60
*15 °С*	1,033	1,068	1,142	1,222	1,307	1,399	1,502
*25 °С*	1,030	1,064	1,137	1,215	1,299	1,391	1,494

	70	80	90	95	97	100
15 °С	1,615	1,732	1,820	1,839	1,841	1,836
25 °С	1,606	1,722	1,809	1,829	1,831	1,827

As can be seen from these data, the determination of the density of the concentration of sulfuric acid above 90 wt. % becomes quite inaccurate.

Water vapor pressure over H 2 SO 4 solutions of different concentrations at different temperatures is shown in fig. 15. Sulfuric acid can act as a drying agent only as long as the water vapor pressure over its solution is less than its partial pressure in the gas being dried.

Rice. 15. Water vapor pressure.

Rice. 16. Boiling points over solutions of H 2 SO 4 . H 2 SO 4 solutions.

Receipt.

The monohydrate can be obtained by crystallization of concentrated sulfuric acid at -10°C.

Sulfuric acid production.

1st stage. Pyrite kiln.

4FeS 2 + 11O 2 --> 2Fe 2 O 3 + 8SO 2 + Q

The process is heterogeneous:

1) grinding iron pyrite (pyrite)

2) "fluidized bed" method

3) 800°С; removal of excess heat

4) increase in the concentration of oxygen in the air

2nd stage.After cleaning, drying and heat exchange, sulfur dioxide enters the contact apparatus, where it is oxidized to sulfuric anhydride (450 ° C - 500 ° C; catalyst V 2 O 5):

2SO2 + O2<-->2SO3

3rd stage. Absorption tower:

nSO 3 + H 2 SO 4 (conc) --> (H 2 SO 4 nSO 3) (oleum)

Water cannot be used due to the formation of fog. Apply ceramic nozzles and the principle of counterflow.

Application.

Remember! Sulfuric acid must be poured into water in small portions, and not vice versa. Otherwise, a violent chemical reaction may occur, as a result of which a person may receive severe burns.

Molecules of pure sulfuric acid.

Fig.1. Diagram of hydrogen bonds in an H 2 SO 4 crystal.

The molecules that form the monohydrate crystal, (HO) 2 SO 2 are connected to each other by fairly strong (25 kJ/mol) hydrogen bonds, as shown schematically in Fig. 1. The (HO) 2 SO 2 molecule itself has the structure of a distorted tetrahedron with a sulfur atom near the center and is characterized by the following parameters: (d (S-OH) \u003d 154 pm, PHO-S-OH \u003d 104 °, d (S \u003d O) \u003d 143 pm, ROSO \u003d 119 °.In the HOSO 3 - ion, d (S-OH) \u003d 161 and d (SO) \u003d 145 pm, and when going to the SO 4 ion, the 2-tetrahedron acquires the correct shape and the parameters are aligned.

Sulfuric acid hydrates.

For sulfuric acid, several crystalline hydrates are known, the composition of which is shown in Fig. 14. Of these, the poorest in water is the oxonium salt: H 3 O + HSO 4 -. Since the system under consideration is very prone to supercooling, the freezing temperatures actually observed in it are much lower than the melting points.

Rice. 14. Melting points in the H 2 O·H 2 SO 4 system.

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