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Properties of sulfuric acid. Chemical properties of molecules of pure sulfuric acid

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). Minor own electrolytic dissociation monohydrate flows in parallel in two directions: [H 3 SO 4 + ]·[НSO 4 - ] = 2·10 -4 and [H 3 O + ]·[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 adding even small amounts of water, 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 + + H SO 4 -<-->2H + + SO 4 2-

The first step (for average concentrations) leads to 100% dissociation:

K2 = ( ) / = 1.2 10-2

1) Interaction with metals:

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

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

Monohydrate (pure, 100% sulfuric acid) is an ionizing solvent that is acidic in nature. Sulfates of many metals dissolve well in it (transforming into bisulfates), while salts of other acids dissolve, as a rule, only if they can be solvolyzed (transforming into bisulfates). Nitric acid behaves in monohydrate as a weak baseHNO 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 turn out to be slightly stronger acids (HSO 3 F > HSO 3 Cl > HClO 4). Monohydrate dissolves well many organic substances containing atoms with lone electron pairs (capable of attaching a proton). Some of them 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. Many metals are also oxidized by it - Cu, Hg, etc. (while gold and platinum are stable with respect to H 2 SO 4). So the interaction with copper follows the equation:

Cu + 2 H 2 SO 4 = CuSO 4 + SO 2 + H 2 O

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

H 2 SO 4 + H 2 S = 2H 2 O + SO 2 + S

It should be noted that it is also partially reduced by hydrogen gas and therefore cannot be used for its drying.

Rice. 13.

The dissolution of concentrated sulfuric acid in water is accompanied by a significant release of heat (and a slight decrease in the total volume of the system). Monohydrate has almost no conductivity electric current. Against, aqueous solutions sulfuric acid are good conductors. As can be seen in Fig. 13, approximately 30% acid has maximum electrical conductivity. The minimum of the curve corresponds to the hydrate with the composition H 2 SO 4 ·H 2 O.

The heat release when dissolving 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 temperature decrease to -37 °C can be achieved.

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, determination by density of the concentration of sulfuric acid above 90 wt. % becomes very inaccurate. The water vapor pressure over solutions of H 2 SO 4 of various concentrations at different temperatures is shown in Fig. 15. Sulfuric acid can act as a desiccant only as long as the pressure of water vapor above its solution is less than its partial pressure in the gas being dried.

Rice. 15.

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

When a dilute solution of sulfuric acid is boiled, water is distilled from it, and the boiling point rises up to 337 ° C, when 98.3% of H 2 SO 4 begins to distill (Fig. 16). On the contrary, excess sulfuric anhydride evaporates from more concentrated solutions. The vapor 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 separate highly volatile acids from their salts when heated (for example, HCl from NaCl).

Receipt

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

Production of sulfuric acid.

1st stage. Furnace for firing pyrites.
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°C; removal of excess heat
4) increase in oxygen concentration in the air
2nd stage. After cleaning, drying and heat exchange, sulfur dioxide enters the contact apparatus, where it is oxidized into 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. Ceramic nozzles and the countercurrent principle are used.

Application.

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

Sulfuric acid is one of the main products of the chemical industry. Used for 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.

It is practically important that very strong (above 75%) sulfuric acid has no effect on iron. This allows it to be stored and transported in steel tanks. On the contrary, dilute H 2 SO 4 easily dissolves iron with the release of hydrogen. Oxidizing properties are not at all characteristic of it.

Strong sulfuric acid vigorously absorbs moisture and is therefore often used to dry gases. From many organic matter containing hydrogen and oxygen, it takes away water, which is often used in technology. This (as well as the oxidizing properties of strong H 2 SO 4) is associated with its destructive effect on plant and animal tissues. Accidentally got on your skin or dress while working sulfuric acid should be washed off immediately with plenty of water, then moisten the affected area with a diluted ammonia solution and rinse again with water.

Author: Chemical Encyclopedia N.S. Zefirov

SULFURIC ACID H2SO4, molecular mass 98.082; colorless odorless oily liquid. A 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, HOSOH angle 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% content of H 2 SO 4, 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 almost completely dissociates into H +, and. Forms hydrates H 2 SO 4 nH 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, 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 increases with increasing 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 SO3 content. As the concentration of aqueous solutions of SULFURIC ACID increases, the total vapor pressure above the solutions decreases and reaches a minimum at a content of 98.3% H 2 SO 4. As the concentration of SO 3 in oleum increases, the total vapor pressure above it increases. The vapor pressure above aqueous solutions of SULFURIC ACID and oleum can be calculated by the equation: logp(Pa) = A - B/T+ 2.126, the values of coefficient A and B depend on the concentration of SULFURIC ACID. Steam above aqueous solutions of SULFURIC ACID consists 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, except for the corresponding azeotropic mixture.

With increasing temperature, the dissociation of H 2 SO 4 H 2 O + SO 3 - Q increases, equation temperature dependence equilibrium constants 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 is: 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 increasing concentration of SULFURIC ACID solutions, their heat capacity decreases and reaches a minimum for 100% SULFURIC ACID; the heat capacity of oleum increases with increasing SO 3 content.

With increasing concentration and decreasing temperature, thermal conductivity l decreases: l = 0.518 + 0.0016t - (0.25 + + t/1293) C/100, where C is the concentration of SULFURIC ACID, in%. Max. The viscosity of oleum H 2 SO 4 SO 3 decreases with increasing temperature. Electric the resistance of SULFURIC ACID 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 increasing temperature r SULFURIC ACID increases. Dielectric permeability 100% SULFURIC ACID k. 101 (298.15 K), 122 (281.15 K); cryoscopic constant 6.12, ebulioscopic. constant 5.33; the diffusion coefficient of SULFURIC ACID vapor in air changes with temperature; D = 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. Razb. H 2 SO 4 interaction with all metals located in the electrochemical voltage series 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). Peroxomonosulfuric (Caro acid) H 2 SO 5 and peroxodisulfuric H 2 S 2 O 8 acids are known (see Sulfur).

Receipt. The raw materials for the production of sulfuric acid are: S, metal sulfides, H 2 S, waste gases of thermal power plants, sulfates of Fe, Ca, etc. Basic. stages of obtaining SULFURIC ACID: 1) roasting of raw materials to produce SO 2; 2) oxidation of SO 2 to SO 3 (conversion); 3) SO 3 absorption. In industry, two methods are used for the production of SULFURIC ACID, differing in the method of SO 2 oxidation - contact using solid catalysts (contacts) and nitrous - with nitrogen oxides. To obtain sulfuric acid by contact method, modern factories use vanadium catalysts, which have replaced Pt and Fe oxides. Pure V 2 O 5 has weak catalytic activity, which increases sharply in the presence of alkali metal salts, with K salts having the most influence. The promoting role of alkali metals is due to the formation of low-melting pyrosulfonadates (3K 2 S 2 O 7 V 2 O 5, 2K 2 S 2 O 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 conditions 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 achieved, the second stage is slow and determines the speed of the process.

The production of SULFURIC ACID from sulfur using 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 SO 2 is cooled in the boiler and, after diluting 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 takes place 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: SO 3 + H 2 O : H 2 SO 4 + + 130.56 kJ. Next, the gas is purified from splashes of SULFURIC ACID, heated to 420 °C and enters the second stage of conversion, which occurs on two layers of catalyst. Before the second stage of absorption, the gas is cooled in the economizer and supplied to the second stage absorber, irrigated with 98% SULFURIC ACID, and then, after cleaning from splashes, is released into the atmosphere.

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

Fig.2. Scheme for the production of sulfuric acid from pyrites: 1-plate feeder; 2-oven; 3-recovery boiler; 4-cyclones; 5-electric precipitators; 6-washing towers; 7-wet electrostatic precipitators; 8-exhaust 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 nitrose method: 1 - denitrate. tower; 2, 3 - first and second products. towers; 4-oxid. tower; 5, 6, 7-absorb. towers; 8 - electric precipitators.

The production of SULFURIC ACID from metal sulfides (Fig. 2) is much more complicated and consists of the following operations. FeS 2 is fired in a fluidized bed furnace using air blast: 4FeS 2 + 11O 2: 2Fe 2 O 3 + 8SO 2 + 13476 kJ. The 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 electric precipitator. Next, the gas passes through two washing towers, irrigated with 40% and 10% SULFURIC ACID. At the same time, the gas is finally cleaned of dust, fluorine and arsenic. To purify the gas from the 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 supplied by a gas blower to the first stage of conversion (3 layers of catalyst). In heat exchangers, the gas is heated to 420 °C thanks to the heat of the gas coming from the first stage of conversion. SO 2, oxidized by 92-95% in SO 3, goes to the first stage of absorption into oleum and monohydrate absorbers, where it is freed from SO 3. Next, the gas containing SO 2 ~ 0.5% enters the second stage of conversion, which takes place on one or two layers of catalyst. The gas is preheated in another group of heat exchangers to 420 °C due to the heat of the gases coming from the second stage of catalysis. After SO 3 is separated in the second absorption stage, the gas is released into the atmosphere.

The degree of conversion of SO 2 to SO 3 using the contact method is 99.7%, the degree of absorption of SO 3 is 99.97%. The production of SULFURIC ACID is carried out in one stage of catalysis, and 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 remaining SO 2 (see Gas purification). The productivity of modern installations is 1500-3100 t/day.

The essence of the nitrose 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 again absorbed by SULFURIC ACID. etc. Nitrogen oxides are not consumed in the nitrous process and are returned to production. cycle, due to their incomplete absorption by SULFURIC ACID, they are partially carried away by exhaust gases. Advantages of the nitrose method: simplicity of instrumentation, lower cost (10-15% lower than contact), the possibility of 100% recycling of SO 2.

The hardware design of the nitrose tower process is simple: SO 2 is processed in 7-8 ceramic-lined towers. nozzle, one of the towers (hollow) is an adjustable oxidizer. volume. The towers have acid collectors, refrigerators, and pumps that supply acid to pressure tanks above the towers. A tail fan is installed in front of the last two towers. An electric precipitator is used to purify the gas from the aerosol 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% recycling of SO 2, a nitrous-free SO 2 processing cycle is installed between the production and absorption zones in combination with the water-acid method of deep capture of nitrogen oxides. The disadvantage of the nitrous method is the low quality of the product: the concentration of SULFURIC ACID is 75%, the presence of nitrogen oxides, Fe and other impurities.

To reduce the possibility of crystallization of SULFURIC ACID during transportation and storage, standards have been established for commercial grades of SULFURIC ACID, the concentration of which corresponds to the lowest crystallization temperatures. Contents SULFURIC ACID 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 with a volume of up to 5000 m 3, their total capacity in the warehouse is designed for ten-day production. Oleum and SULFURIC ACID are transported in steel railway tanks. Conc. and battery SULFURIC ACID are transported in tanks made of acid-resistant steel. Tanks for transporting 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 industry. organic synthesis in dehydration reactions (production of diethyl ether, esters), hydration (ethanol from ethylene), sulfonation (synthetic detergents and intermediate products in the production of dyes), alkylation (production of isooctane, polyethylene glycol, capro-lactam), etc. The largest consumer of SULFURIC ACID is the production of mineral fertilizers. For 1 t of P 2 O 5 phosphorus fertilizers, 2.2-3.4 t of SULFURIC ACID is consumed, and for 1 t of (NH 4) 2 SO 4 -0.75 t of SULFURIC ACID is consumed. Therefore, they tend to build sulfuric acid plants 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, causing difficulty breathing, coughing, often laryngitis, tracheitis, bronchitis, etc. MPC of aerosol SULPHURIC ACID in the air of working area 1, 0 mg/m3, at atm. air 0.3 mg/m 3 (max. one-time) and 0.1 mg/m 3 (daily average). The damaging concentration of SULFURIC ACID vapors is 0.008 mg/l (exposure 60 min), lethal 0.18 mg/l (60 min). 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 in the form of acid rain.

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

Chemical encyclopedia. Volume 4 >>

Physical properties.

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). Minor intrinsic electrolytic dissociation of the monohydrate proceeds in parallel in two directions: [H 3 SO 4 + ]·[НSO 4 - ] = 2·10 -4 and [H 3 O + ]·[НS 2 О 7 - ] = 4·10 - 5 . Its molecular ionic composition can be approximately characterized by the following data (in%):

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

When adding even small amounts of water, dissociation becomes predominant according to the following 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 + + H SO 4 -<-->2H + + SO 4 2-

The first step (for average concentrations) leads to 100% dissociation:

K 2 = ( ) / = 1.2 10 -2

1) Interaction with metals:

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

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

b) concentrated H 2 +6 SO 4 is 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 + H 2 SO 4 --> 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 - like a very weak acid

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

Fluorosulfonic and chlorosulfonic acids turn out to be slightly stronger acids (HSO 3 F > HSO 3 Cl > HClO 4). Monohydrate dissolves well many organic substances containing atoms with lone electron pairs (capable of attaching a proton). Some of them 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 = CuSO 4 + SO 2 + H 2 O

H 2 SO 4 + H 2 S = 2H 2 O + SO 2 + S

It should be noted that it is also partially reduced by hydrogen gas and therefore cannot be used for its drying.

Rice. 13. Electrical conductivity of sulfuric acid solutions.

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

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 °C*	1,033	1,068	1,142	1,222	1,307	1,399	1,502
*25 °C*	1,030	1,064	1,137	1,215	1,299	1,391	1,494

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

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

The water vapor pressure over solutions of H 2 SO 4 of various concentrations at different temperatures is shown in Fig. 15. Sulfuric acid can act as a desiccant only as long as the pressure of water vapor above 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.

Production of sulfuric acid.

1st stage. Furnace for firing pyrites.

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°C; removal of excess heat

4) increase in oxygen concentration in the air

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

2SO2 + O2<-->2SO 3

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. Ceramic nozzles and the countercurrent principle are used.

Application.

Remember! Sulfuric acid should be poured into water in small portions, and not vice versa. Otherwise, a violent chemical reaction may occur, resulting in severe burns.

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

Strong sulfuric acid vigorously absorbs moisture and is therefore often used to dry gases. It removes water from many organic substances containing hydrogen and oxygen, which is often used in technology. This (as well as the oxidizing properties of strong H 2 SO 4) is associated with its destructive effect on plant and animal tissues. If sulfuric acid accidentally gets on your skin or dress while working, you should immediately wash it off with plenty of water, then moisten the affected area with a diluted ammonia solution and rinse again with water.

Molecules of pure sulfuric acid.

Fig.1. Scheme 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) = 154 pm, PHO-S-OH = 104°, d(S=O) = 143 pm, POSO = 119°. In the HOSO 3 - ion, d(S-OH) = 161 and d(SO) = 145 pm, and when moving to the SO 4 2- ion, the tetrahedron acquires the correct shape and the parameters are aligned.

Crystal hydrates of sulfuric acid.

Several crystalline hydrates are known for sulfuric acid, 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 actual freezing temperatures observed in it are much lower than the melting temperatures.

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

DEFINITION

Anhydrous sulfuric acid is a heavy, viscous liquid that is easily miscible with water in any proportion: the interaction is characterized by an extremely 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's why it's so important to always use reverse order in preparing solutions and add acid to 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 unusually high dielectric constant and very high electrical conductivity, which is due to ionic autodissociation (autoprotolysis) of the compound, as well as the relay conduction mechanism with proton transfer, which ensures the flow of electric current through a viscous liquid with a large number hydrogen bonds.

Table 1. Physical properties of sulfuric acid.

Preparation of sulfuric acid

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

Concentrated sulfuric acid (“oil of vitriol”) was first obtained by heating “green vitriol” FeSO 4 × nH 2 O and was consumed in large quantities to produce Na 2 SO 4 and NaCl.

IN modern process To produce sulfuric acid, a catalyst consisting of vanadium(V) oxide with the addition of potassium sulfate on a carrier of silicon dioxide or kieselguhr is used. Sulfur dioxide SO2 is produced 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. SO2 is then 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 step, in solutions of low concentration, it dissociates almost completely:

H 2 SO 4 ↔H + + HSO 4 - .

Second stage dissociation

HSO 4 — ↔H + + SO 4 2-

occurs 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. Average 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 = 4I 2 + H 2 S + 4H 2 O;

2HBr + H 2 SO 4 = Br 2 + SO 2 + 2H 2 O;

C + 2H 2 SO 4 = CO 2 + 2SO 2 + 2H 2 O;

S + 2H 2 SO 4 = 3SO 2 + 2H 2 O.

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

Zn + H 2 SO 4 = ZnSO 4 + H 2.

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

Concentrated sulfuric acid is an oxidizing agent due to sulfur (VI). It oxidizes metals in the voltage range up to and including silver. The products of its reduction may vary depending on the activity of the metal and the conditions (acid concentration, temperature). When interacting with little active metals, for example with copper, the acid is reduced to SO 2:

Cu + 2H 2 SO 4 = CuSO 4 + SO 2 + 2H 2 O.

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

Zn + 2H 2 SO 4 = ZnSO 4 + SO 2 + 2H 2 O;

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

4Zn + 5H 2 SO 4 = 4ZnSO 4 + H 2 S + 4H 2 O.

Application of sulfuric acid

The use of sulfuric acid varies from country to country and from decade to decade. For example, in the USA, the main area of consumption of H 2 SO 4 is currently the production of fertilizers (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 H2SO4 produced is used in the production of fertilizers, but 18% goes to paints, pigments and semi-products of dye production, 16% to chemical production, 12% to the production of soaps 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 (IV) oxide in the roasting reaction is 90%, and sulfur (VI) oxide in the catalytic oxidation of sulfur (IV) is 95% of theoretical.

Solution

Let us write the equation for the pyrite firing reaction:

4FeS 2 + 11O 2 = 2Fe 2 O 3 + 8SO 2.

Let's calculate the amount of pyrite substance:

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

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

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

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

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

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

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

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

2SO 2 + O 2 = 2SO 3.

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

n(SO 3) theor = n(SO 2) pract = 15 kmol.

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

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

Let us write the reaction equation for the production of sulfuric acid:

SO 3 + H 2 O = H 2 SO 4.

Let's find the amount of sulfuric acid:

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

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

m(H 2 SO 4) = n(H 2 SO 4) × M(H 2 SO 4);

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

m(H 2 SO 4) = 14.25 × 98 = 1397 kg.

Answer

The mass of sulfuric acid is 1397 kg

Properties of sulfuric acid

Anhydrous sulfuric acid (monohydrate) is a heavy oily liquid that mixes with water in all proportions, releasing a large amount of heat. Density at 0 °C is 1.85 g/cm3. It boils at 296 °C and freezes at - 10 °C. Sulfuric acid is called not only monohydrate, but also aqueous solutions of it (), as well as solutions of sulfur trioxide in monohydrate (), called oleum. Oleum “smoke” in air due to desorption from it. Pure sulfuric acid is colorless, while technical sulfuric acid is colored dark by impurities.

The physical properties of sulfuric acid, such as density, crystallization temperature, boiling point, depend on its composition. In Fig. Figure 1 shows a crystallization diagram of the system. The maxima in it correspond to the composition of the compounds or the presence of minima is explained by the fact that the crystallization temperature of mixtures of two substances is lower than the crystallization temperature of each of them.

Rice. 1

Anhydrous 100% sulfuric acid has a relatively high crystallization temperature of 10.7 °C. To reduce the possibility of freezing of a commercial product during transportation and storage, the concentration of technical sulfuric acid is chosen such that it has a sufficiently low crystallization temperature. The industry produces three types of commercial sulfuric acid.

Sulfuric acid is very active. It dissolves metal oxides and most pure metals; at elevated temperatures, it displaces all other acids from salts. Sulfuric acid combines especially greedily with water due to its ability to form hydrates. It takes water away from other acids, from crystalline hydrates of salts and even oxygen derivatives of hydrocarbons, which contain not water as such, but hydrogen and oxygen in the combination H:O = 2. wood and other plant and animal tissues containing cellulose, starch and sugar are destroyed in concentrated sulfuric acid; the water binds with the acid and only finely dispersed carbon remains from the tissue. In dilute acid, cellulose and starch break down to form sugars. If concentrated sulfuric acid comes into contact with human skin, it causes burns.

The high activity of sulfuric acid, combined with the relatively low cost of production, predetermined the enormous scale and extreme diversity of its application (Fig. 2). It is difficult to find an industry in which sulfuric acid or products made from it were not consumed in varying quantities.

Rice. 2

The largest consumer of sulfuric acid is the production of mineral fertilizers: superphosphate, ammonium sulfate, etc. many acids (for example, phosphoric, acetic, hydrochloric) and salts are produced largely using sulfuric acid. Sulfuric acid is widely used in the production of non-ferrous and rare metals. In the metalworking industry, sulfuric acid or its salts are used for pickling steel products before painting, tinning, nickel plating, chrome plating, etc. Significant amounts of sulfuric acid are spent on refining petroleum products. The production of a number of dyes (for fabrics), varnishes and paints (for buildings and machines), medicinal substances and some plastics also involves the use of sulfuric acid. Using sulfuric acid, ethyl and other alcohols, some esters, synthetic detergents, and a number of pesticides for controlling agricultural pests and weeds are produced. Dilute solutions of sulfuric acid and its salts are used in the production of artificial silk, in textile industry for processing fibers or fabrics before dyeing them, as well as in other light industries. IN Food Industry sulfuric acid is used in the production of starch, molasses and a number of other products. Transport uses lead sulfuric acid batteries. Sulfuric acid is used for drying gases and for concentrating acids. Finally, sulfuric acid is used in nitration processes and in the production of most explosives.