Properties of sulfuric acid

Anhydrous sulfuric acid(monohydrate) is a heavy oily liquid that mixes with water in all proportions to release large quantity 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.

Physical properties 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 sufficient low temperature crystallization. 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 production 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 quantities sulfuric acid is spent on purifying 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, a range of pesticides for pest control Agriculture and weeds. Dilute solutions of sulfuric acid and its salts are used in the production of rayon, in the textile industry for treating fibers or fabrics before dyeing, as well as in other industries light industry. 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.

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 very high value dielectric constant (e = 100 at 25 °C). Minor intrinsic electrolytic dissociation of the monohydrate proceeds in parallel in two directions: [H 3 SO 4 + ]·[HSO 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 unshared electron pairs(capable of adding 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. 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 a 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. Water vapor pressure over solutions of H 2 SO 4 of various concentrations at different temperatures 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 sulphur 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, a violent chemical reaction may occur, resulting in severe burns.

Sulfuric acid is one of the main products chemical industry. Used for the production of mineral fertilizers (superphosphate, ammonium sulfate), various acids and salts, medicinal 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. 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.

Sulfur is chemical element, which is in the sixth group and third period of the periodic table. In this article we will take a detailed look at its chemical properties, production, use, and so on. The physical characteristic includes such characteristics as color, level of electrical conductivity, boiling point of sulfur, etc. Chemical characteristics describe its interaction with other substances.

Sulfur from a physics point of view

This is a fragile substance. At normal conditions it is in a solid state of aggregation. Sulfur has a lemon-yellow color.

And for the most part, all its compounds have yellow tints. Does not dissolve in water. It has low thermal and electrical conductivity. These characteristics characterize it as a typical non-metal. Although chemical composition sulfur is not at all complicated; this substance can have several variations. It all depends on the structure crystal lattice, with the help of which atoms are connected, but they do not form molecules.

So, the first option is rhombic sulfur. It is the most stable. The boiling point of this type of sulfur is four hundred and forty-five degrees Celsius. But in order for this substance to turn into gaseous state of aggregation, he first needs to go through the liquid. So, the melting of sulfur occurs at a temperature of one hundred and thirteen degrees Celsius.

The second option is monoclinic sulfur. It is a needle-shaped crystal with a dark yellow color. Melting the first type of sulfur and then slowly cooling it leads to the formation of this type. This variety has almost the same physical characteristics. For example, the boiling point of this type of sulfur is the same four hundred and forty-five degrees. In addition, there is such a variety of this substance as plastic. It is obtained by pouring into cold water heated almost to boiling rhombic. The boiling point of this type of sulfur is the same. But the substance has the property of stretching like rubber.

One more component physical characteristics, which I would like to talk about is the ignition temperature of sulfur.

This indicator may vary depending on the type of material and its origin. For example, the ignition temperature of technical sulfur is one hundred and ninety degrees. This is a fairly low figure. In other cases, the flash point of sulfur can be two hundred forty-eight degrees and even two hundred fifty-six. It all depends on what material it was extracted from and what its density is. But we can conclude that the combustion temperature of sulfur is quite low, compared to other chemical elements; it is a flammable substance. In addition, sometimes sulfur can combine into molecules consisting of eight, six, four or two atoms. Now, having considered sulfur from a physics point of view, let's move on to the next section.

Chemical characteristics of sulfur

This element has a relatively low atomic mass, it is equal to thirty-two grams per mole. The characteristics of the element sulfur include such a feature of this substance as the ability to have to varying degrees oxidation. This differs from, say, hydrogen or oxygen. Considering the question of what chemical characterization element sulfur, it is impossible not to mention that, depending on conditions, it exhibits both reducing and oxidizing properties. So, let’s look at the interaction of this substance with various chemical compounds in order.

Sulfur and simple substances

Simple substances are substances that contain only one chemical element. Its atoms may combine into molecules, as, for example, in the case of oxygen, or they may not combine, as is the case with metals. Thus, sulfur can react with metals, other non-metals and halogens.

Interaction with metals

To carry out this kind of process, high temperature is required. Under these conditions, an addition reaction occurs. That is, metal atoms combine with sulfur atoms, thereby forming complex substances sulfides. For example, if you heat two moles of potassium and mix them with one mole of sulfur, you get one mole of sulfide of this metal. The equation can be written as follows: 2K + S = K 2 S.

Reaction with oxygen

This is the burning of sulfur. Due to this process its oxide is formed. The latter can be of two types. Therefore, sulfur combustion can occur in two stages. The first is when one mole of sulfur dioxide is formed from one mole of sulfur and one mole of oxygen. The equation for this chemical reaction can be written as follows: S + O 2 = SO 2. The second stage is the addition of another oxygen atom to the dioxide. This happens if you add one mole of oxygen to two moles under conditions high temperature. The result is two moles of sulfur trioxide. Equation of this chemical interaction looks like this: 2SO 2 + O 2 = 2SO 3. As a result of this reaction, sulfuric acid is formed. So, having carried out the two described processes, you can pass the resulting trioxide through a stream of water vapor. And we get The equation for such a reaction is written as follows: SO 3 + H 2 O = H 2 SO 4.

Interaction with halogens

Chemicals, like other non-metals, allow it to react with a given group of substances. It includes compounds such as fluorine, bromine, chlorine, iodine. Sulfur reacts with any of them except the last one. As an example, we can cite the process of fluoridation of the element of the periodic table we are considering. By heating the mentioned non-metal with a halogen, two variations of fluoride can be obtained. The first case: if we take one mole of sulfur and three moles of fluorine, we get one mole of fluoride, the formula of which is SF 6. The equation looks like this: S + 3F 2 = SF 6. In addition, there is a second option: if we take one mole of sulfur and two moles of fluorine, we get one mole of fluoride with the chemical formula SF 4. The equation is written as follows: S + 2F 2 = SF 4. As you can see, it all depends on the proportions in which the components are mixed. In exactly the same way, the process of sulfur chlorination (two different substances can also be formed) or bromination can be carried out.

Interaction with other simple substances

The characteristics of the element sulfur do not end there. The substance can also react chemically with hydrogen, phosphorus and carbon. Due to interaction with hydrogen, sulfide acid is formed. As a result of its reaction with metals, their sulfides can be obtained, which, in turn, are also obtained directly by reacting sulfur with the same metal. The addition of hydrogen atoms to sulfur atoms occurs only under very high temperature conditions. When sulfur reacts with phosphorus, its phosphide is formed. It has the following formula: P 2 S 3. In order to get one mole of this substance, you need to take two moles of phosphorus and three moles of sulfur. When sulfur interacts with carbon, a carbide of the nonmetal in question is formed. Its chemical formula looks like this: CS 2. In order to get one mole of a given substance, you need to take one mole of carbon and two moles of sulfur. All the addition reactions described above occur only when the reagents are heated to high temperatures. We have looked at the interaction of sulfur with simple substances, now let's move on to the next point.

Sulfur and complex compounds

Complex substances are those substances whose molecules consist of two (or more) different elements. The chemical properties of sulfur allow it to react with compounds such as alkalis, as well as concentrated sulfate acid. Its reactions with these substances are quite peculiar. First, let's look at what happens when the nonmetal in question is mixed with alkali. For example, if you take six moles and add three moles of sulfur, you get two moles of potassium sulfide, one mole of potassium sulfite and three moles of water. This kind of reaction can be expressed the following equation: 6KOH + 3S = 2K 2 S + K2SO 3 + 3H 2 O. The same principle of interaction occurs if you add Next, consider the behavior of sulfur when a concentrated solution of sulfate acid is added to it. If we take one mole of the first and two moles of the second substance, we obtain the following products: sulfur trioxide in an amount of three moles, as well as water - two moles. This chemical reaction can only occur when the reactants are heated to a high temperature.

Obtaining the non-metal in question

There are several main ways in which sulfur can be extracted from a variety of substances. The first method is to isolate it from pyrite. Chemical formula the latter - FeS 2. When this substance is heated to a high temperature without access to oxygen, another iron sulfide - FeS - and sulfur can be obtained. The reaction equation is written as follows: FeS 2 = FeS + S. The second method of producing sulfur, which is often used in industry, is the combustion of sulfur sulfide under the condition of a small amount of oxygen. In this case, you can get the nonmetal in question and water. To carry out the reaction, you need to take the components in a molar ratio of two to one. As a result, we obtain the final products in proportions of two to two. The equation for this chemical reaction can be written as follows: 2H 2 S + O 2 = 2S + 2H 2 O. In addition, sulfur can be obtained through a variety of metallurgical processes, for example, in the production of metals such as nickel, copper and others.

Industrial use

The nonmetal we are considering has found its widest application in the chemical industry. As mentioned above, here it is used to produce sulfate acid from it. In addition, sulfur is used as a component for making matches, due to the fact that it is a flammable material. It is also indispensable in the production of explosives, gunpowder, sparklers, etc. In addition, sulfur is used as one of the ingredients in pest control products. In medicine, it is used as a component in the manufacture of medicines for skin diseases. The substance in question is also used in the production of various dyes. In addition, it is used in the manufacture of phosphors.

Electronic structure of sulfur

As you know, all atoms consist of a nucleus in which there are protons - positively charged particles - and neutrons, i.e. particles with zero charge. Electrons with a negative charge rotate around the nucleus. For an atom to be neutral, it must have the same number of protons and electrons in its structure. If there are more of the latter, this is already negative ion- anion. If, on the contrary, the number of protons is greater than electrons, this is positive ion, or cation. The sulfur anion can act as an acid residue. It is part of the molecules of substances such as sulfide acid (hydrogen sulfide) and metal sulfides. The anion is formed during electrolytic dissociation, which occurs when a substance dissolves in water. In this case, the molecule breaks down into a cation, which can be presented in the form of a metal or hydrogen ion, as well as a cation - an ion of an acidic residue or hydroxyl group(HE-).

Because serial number sulfur in the periodic table is sixteen, then we can conclude that its nucleus contains exactly this number of protons. Based on this, we can say that there are also sixteen electrons rotating around. The number of neutrons can be found by subtracting from molar mass serial number of a chemical element: 32 - 16 = 16. Each electron does not rotate randomly, but in a specific orbit. Since sulfur is a chemical element that belongs to the third period of the periodic table, there are three orbits around the nucleus. The first of them has two electrons, the second has eight, and the third has six. Electronic formula sulfur atom is written as follows: 1s2 2s2 2p6 3s2 3p4.

Prevalence in nature

Basically, the chemical element in question is found in minerals, which are sulfides of various metals. First of all, it is pyrite - an iron salt; It is also lead, silver, copper luster, zinc blende, cinnabar - mercury sulfide. In addition, sulfur can also be part of minerals, the structure of which is represented by three or more chemical elements.

For example, chalcopyrite, mirabilite, kieserite, gypsum. You can consider each of them in more detail. Pyrite is ferrum sulfide, or FeS 2 . It has a light yellow color with a golden sheen. This mineral can often be found as an impurity in lapis lazuli, which is widely used for making jewelry. This is due to the fact that these two minerals often have a common deposit. Copper luster - chalcocite, or chalcocite - is a bluish-gray substance similar to metal. and silver luster (argentite) have similar properties: they both resemble metals in appearance and have a gray color. Cinnabar is a dull brownish-red mineral with gray flecks. Chalcopyrite, the chemical formula of which is CuFeS 2, is golden yellow, it is also called gold blende. Zinc blende (sphalerite) can range in color from amber to fiery orange. Mirabilite - Na 2 SO 4 x10H 2 O - transparent or white crystals. It is also called used in medicine. The chemical formula of kieserite is MgSO 4 xH 2 O. It looks like a white or colorless powder. The chemical formula of gypsum is CaSO 4 x2H 2 O. In addition, this chemical element is part of the cells of living organisms and is an important trace element.

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 an unusually high dielectric constant and very high electrical conductivity, which is caused by ionic autodissociation (autoprotolysis) of the compound, as well as the relay mechanism of conductivity with proton transfer, ensuring 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 ​​H 2 SO 4 consumption is currently the production of fertilizers (70%), followed by chemical production, metallurgy, and 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

sulfuric acid, sulfuric acid formula
Sulfuric acid H2SO4 is a strong dibasic acid, corresponding to highest degree sulfur oxidation (+6). Under normal conditions, concentrated sulfuric acid is a heavy, oily liquid, colorless and odorless, with a sour “copper” taste. In technology, sulfuric acid is a mixture of both water and sulfuric anhydride SO3. If the molar ratio of SO3:H2O< 1, то это водный раствор серной кислоты, если >1 - solution of SO3 in sulfuric acid (oleum).

• 1 Title
• 2 Physical and physico-chemical properties
  • 2.1 Oleum
• 3 Chemical properties
• 4 Application
• 5 Toxic effect
• 6 Historical information
• 7 Additional information
• 8 Preparation of sulfuric acid
  • 8.1 First method
  • 8.2 Second method
• 9 Standards
• 10 Notes
• 11 Literature
• 12 Links

Name

IN XVIII-XIX centuries sulfur for gunpowder was produced from sulfur pyrite (pyrite) in vitriol factories. Sulfuric acid at that time was called " oil of vitriol"(as a rule, it was a crystalline hydrate, with a consistency reminiscent of oil), obviously this is where the origin of the name of its salts (or rather crystalline hydrates) comes from - vitriol.

Physical and physico-chemical properties

Very strong acid, at 18°C ​​pKa (1) = −2.8, pKa (2) = 1.92 (K₂ 1.2 10−2); bond lengths in the molecule S=O 0.143 nm, S-OH 0.154 nm, HOSOH angle 104°, OSO 119°; boils, forming an azeotropic mixture (98.3% H2SO4 and 1.7% H2O with a boiling point of 338.8oC). Sulfuric acid corresponding to 100% H2SO4 content has the following composition (%): H2SO4 99.5, HSO4− - 0.18, H3SO4+ - 0.14, H3O+ - 0.09, H2S2O7 - 0.04, HS2O7⁻ - 0.05. Miscible with water and SO3, in all proportions. In aqueous solutions, sulfuric acid almost completely dissociates into H3O+, HSO3+, and 2HSO₄−. Forms H2SO4 nH2O hydrates, where n = 1, 2, 3, 4 and 6.5.

Oleum

Solutions of sulfuric anhydride SO3 in sulfuric acid are called oleum, they form two compounds H2SO4 SO3 and H2SO4 2SO3.

Oleum also contains pyrosulfuric acids, obtained by the reactions:

The boiling point of aqueous solutions of sulfuric acid increases with increasing its concentration and reaches a maximum at a content of 98.3% H2SO4.

The boiling point of oleum decreases with increasing SO3 content. With increasing concentration of aqueous solutions of sulfuric acid total pressure vapor above the solutions decreases and reaches a minimum at a content of 98.3% H2SO4. As the concentration of SO3 in oleum increases, the total vapor pressure above it increases. Steam pressure above aqueous solutions sulfuric acid and oleum can be calculated using the equation:

the values ​​of the coefficients A and depend on the concentration of sulfuric acid. Vapor over aqueous solutions of sulfuric acid consists of a mixture of water vapor, H2SO4 and SO3, and 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, dissociation increases:

Equation for the temperature dependence of the equilibrium constant:

At normal pressure, 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:

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 SO3 content.

With increasing concentration and decreasing temperature, thermal conductivity λ decreases:

where C is the concentration of sulfuric acid, in%.

Oleum H2SO4·SO3 has the maximum viscosity; with increasing temperature, η decreases. Electrical resistance sulfuric acid is minimal at a concentration of SO3 and 92% H2SO4 and maximum at a concentration of 84 and 99.8% H2SO4. For oleum, the minimum ρ is at a concentration of 10% SO3. With increasing temperature, ρ of sulfuric acid increases. The dielectric constant 100% sulfuric acid 101 (298.15 K), 122 (281.15 K); cryoscopic constant 6.12, ebullioscopic constant 5.33; the diffusion coefficient of sulfuric acid vapor in air varies depending on temperature; D = 1.67·10⁻⁵T3/2 cm²/s.

Chemical properties

Sulfuric acid in concentrated form when heated is a fairly strong oxidizing agent; oxidizes HI and partially HBr to free halogens, carbon to CO2, sulfur to SO2, oxidizes many metals (Cu, Hg, with the exception of gold and platinum). In this case, concentrated sulfuric acid is reduced to SO2, for example:

The most powerful reducing agents reduce concentrated sulfuric acid to S and H2S. Concentrated sulfuric acid absorbs water vapor, so it is used for drying gases, liquids and solids, for example, in desiccators. However, concentrated H2SO4 is partially reduced by hydrogen, which is why it cannot be used for drying. Splitting off water from organic compounds and leaving behind black carbon (charcoal), concentrated sulfuric acid causes charring of wood, sugar and other substances.

Dilute H2SO4 reacts with all metals found in electrochemical series voltages to the left of hydrogen with its release, for example:

The oxidizing properties of dilute H2SO4 are uncharacteristic. Sulfuric acid forms two series of salts: medium - sulfates and acidic - hydrosulfates, as well as esters. Peroxomonosulfuric acid (or Caro acid) H2SO5 and peroxodisulfuric acid H2S2O8 are known.

Sulfuric acid also reacts with basic oxides, forming sulfate and water:

In metalworking plants, a solution of sulfuric acid is used to remove a layer of metal oxide from the surface of metal products that are subjected to high heat during the manufacturing process. Thus, iron oxide is removed from the surface of sheet iron by the action of a heated solution of sulfuric acid:

A qualitative reaction to sulfuric acid and its soluble salts is their interaction with soluble barium salts, which results in the formation of a white precipitate of barium sulfate, insoluble in water and acids, for example:

Application

Sulfuric acid is used:

• in ore processing, especially during mining rare elements, incl. uranium, iridium, zirconium, osmium, etc.;
• in the production of mineral fertilizers;
• as an electrolyte in lead batteries;
• to obtain various mineral acids and salts;
• in the production of chemical fibers, dyes, smoke-forming and explosives;
• in the oil, metalworking, textile, leather and other industries;
• in the food industry - registered as food additives E513(emulsifier);
• in industrial organic synthesis in reactions:
  • dehydration (production of diethyl ether, esters);
  • hydration (ethanol from ethylene);
  • sulfonation (synthetic detergents and intermediates in the production of dyes);
  • alkylation (production of isooctane, polyethylene glycol, caprolactam), etc.
  • For the restoration of resins in filters in the production of distilled water.

World production of sulfuric acid is approx. 160 million tons per year. The largest consumer of sulfuric acid is the production of mineral fertilizers. P₂O₅ phosphorus fertilizers consume 2.2-3.4 times more mass of sulfuric acid, and (NH₄)₂SO₄ sulfuric acid consumes 75% of the mass of consumed (NH₄)₂SO₄. Therefore, they tend to build sulfuric acid plants in conjunction with factories for the production of mineral fertilizers.

Toxic effect

Sulfuric acid and oleum are very corrosive substances. They affect the skin, mucous membranes, Airways(cause chemical burns). When inhaling vapors of these substances, they cause difficulty breathing, coughing, and often laryngitis, tracheitis, bronchitis, etc. The maximum permissible concentration of sulfuric acid aerosol in the air of the working area is 1.0 mg/m³, in atmospheric air 0.3 mg/m³ (maximum one-time) and 0.1 mg/m³ (average daily). The damaging concentration of sulfuric acid vapor is 0.008 mg/l (exposure 60 min), lethal 0.18 mg/l (60 min). Hazard class II. An aerosol of sulfuric acid can form in the atmosphere as a result of emissions from chemical and metallurgical industries containing S oxides and fall in the form of acid rain.

Historical information

Sulfuric acid has been known since ancient times, occurring in nature in free form, for example, in the form of lakes near volcanoes. Perhaps the first mention of acid gases produced by the calcination of alum or iron sulfate of the “green stone” is found in writings attributed to the Arab alchemist Jabir ibn Hayyan.

In the 9th century, the Persian alchemist Ar-Razi, calcining a mixture of iron and copper sulfate(FeSO4 7H2O and CuSO4 5H2O), also obtained a solution of sulfuric acid. This method was perfected by the European alchemist Albert Magnus, who lived in the 13th century.

Scheme for obtaining sulfuric acid from iron sulfate - thermal decomposition iron (II) sulfate followed by cooling the mixture

Dalton sulfuric acid molecule

1. 2FeSO4+7H2O→Fe2O3+SO2+H2O+O2
2. SO2+H2O+1/2O2 ⇆ H2SO4

The works of the alchemist Valentin (13th century) describe a method for producing sulfuric acid by absorbing gas (sulfuric anhydride) released by burning a mixture of sulfur and nitrate powders with water. Subsequently, this method formed the basis of the so-called. “chamber” method, carried out in small chambers lined with lead, which does not dissolve in sulfuric acid. In the USSR, this method existed until 1955.

Alchemists of the 15th century also knew a method for producing sulfuric acid from pyrite - sulfur pyrite, a cheaper and more common raw material than sulfur. Sulfuric acid has been produced this way for 300 years. small quantities in glass retorts. Subsequently, in connection with the development of catalysis, this method replaced the chamber method for the synthesis of sulfuric acid. Currently, sulfuric acid is produced by the catalytic oxidation (on V2O5) of sulfur oxide (IV) to sulfur oxide (VI), and subsequent dissolution of sulfur oxide (VI) in 70% sulfuric acid to form oleum.

In Russia, the production of sulfuric acid was first organized in 1805 near Moscow in the Zvenigorod district. In 1913, Russia ranked 13th in the world in sulfuric acid production.

additional information

Tiny droplets of sulfuric acid can form in medium and upper layers atmosphere as a result of the reaction of water vapor and volcanic ash containing large quantities sulfur. The resulting suspension, due to the high albedo of sulfuric acid clouds, makes access difficult sun rays to the surface of the planet. Therefore (and also as a result of the large number tiny particles volcanic ash in the upper atmosphere, also making access difficult sunlight to the planet) after particularly strong volcanic eruptions Significant climate changes may occur. For example, as a result of the eruption of the Ksudach volcano (Kamchatka Peninsula, 1907) increased concentration dust remained in the atmosphere for about 2 years, and characteristic noctilucent clouds of sulfuric acid were observed even in Paris. The explosion of Mount Pinatubo in 1991, which released 3 107 tons of sulfur into the atmosphere, resulted in 1992 and 1993 being significantly colder than 1991 and 1994.

Preparation of sulfuric acid

First way

Second way

In those rare cases when hydrogen sulfide (H2S) displaces sulfate (SO4-) from a salt (with metals Cu, Ag, Pb, Hg) the by-product is sulfuric acid

Sulfides of these metals have the highest strength, as well as a distinctive black color.

Standards

• Technical sulfuric acid GOST 2184-77
• Battery sulfuric acid. Specifications GOST 667-73
• Sulfuric acid of special purity. Technical specifications GOST 1422-78
• Reagents. Sulfuric acid. Technical specifications GOST 4204-77

Notes

1. Ushakova N. N., Figurnovsky N. A. Vasily Mikhailovich Severgin: (1765-1826) / Ed. I. I. Shafranovsky. M.: Nauka, 1981. P. 59.
2. 1 2 3 Khodakov Yu.V., Epshtein D.A., Gloriozov P.A. § 91. Chemical properties of sulfuric acid // Inorganic chemistry: Textbook for grades 7-8 high school. - 18th ed. - M.: Education, 1987. - P. 209-211. - 240 s. - 1,630,000 copies.
3. Khodakov Yu.V., Epshtein D.A., Gloriozov P.A. § 92. Qualitative reaction on sulfuric acid and its salts // Inorganic chemistry: Textbook for grades 7-8 of secondary school. - 18th ed. - M.: Education, 1987. - P. 212. - 240 p. - 1,630,000 copies.
4. ballet artistic director's face Bolshoi Theater Sulfuric acid was splashed on Sergei Filin
5. Epstein, 1979, p. 40
6. Epstein, 1979, p. 41
7. see article “Volcanoes and climate” (Russian)
8. Russian Archipelago - Is humanity to blame for global change climate? (Russian)

Literature

• Handbook of sulfuric acid, ed. K. M. Malina, 2nd ed., M., 1971
• Epshtein D. A. General chemical Technology. - M.: Chemistry, 1979. - 312 p.

Links

• Article “Sulfuric acid” (Chemical Encyclopedia)
• Density and pH value of sulfuric acid at t=20 °C

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