The +4 oxidation state for sulfur is quite stable and manifests itself in SHal 4 tetrahalides, SOHal 2 oxodihalides, SO 2 dioxide, and their corresponding anions. We will get acquainted with the properties of sulfur dioxide and sulfurous acid.
1.11.1. Sulfur oxide (IV) The structure of the so2 molecule
The structure of the SO 2 molecule is similar to the structure of the ozone molecule. The sulfur atom is in a state of sp 2 hybridization, the shape of the orbitals is a regular triangle, the shape of the molecule is angular. The sulfur atom has an unshared electron pair. The S-O bond length is 0.143 nm, the bond angle is 119.5°.
The structure corresponds to the following resonant structures:
Unlike ozone, the S–O bond multiplicity is 2, i.e., the first resonance structure makes the main contribution. The molecule is characterized by high thermal stability.
Physical Properties
Under normal conditions, sulfur dioxide or sulfur dioxide is a colorless gas with a pungent suffocating odor, melting point -75 °C, boiling point -10 °C. Let's well dissolve in water, at 20 °C in 1 volume of water 40 volumes of sulfur dioxide are dissolved. Toxic gas.
Chemical properties of sulfur oxide (IV)
Sulfur dioxide is highly reactive. Sulfur dioxide is an acid oxide. It is quite soluble in water with the formation of hydrates. It also partially interacts with water, forming a weak sulfurous acid, which is not isolated individually:
SO 2 + H 2 O \u003d H 2 SO 3 \u003d H + + HSO 3 - \u003d 2H + + SO 3 2-.
As a result of dissociation, protons are formed, so the solution has an acidic environment.
When sulfur dioxide gas is passed through a sodium hydroxide solution, sodium sulfite is formed. Sodium sulfite reacts with excess sulfur dioxide to form sodium hydrosulfite:
2NaOH + SO 2 = Na 2 SO 3 + H 2 O;
Na 2 SO 3 + SO 2 \u003d 2NaHSO 3.
Sulfur dioxide is characterized by redox duality, for example, it, showing reducing properties, discolors bromine water:
SO 2 + Br 2 + 2H 2 O \u003d H 2 SO 4 + 2HBr
and potassium permanganate solution:
5SO 2 + 2KMnO 4 + 2H 2 O \u003d 2KНSO 4 + 2MnSO 4 + H 2 SO 4.
oxidized by oxygen to sulfuric anhydride:
2SO 2 + O 2 \u003d 2SO 3.
It exhibits oxidizing properties when interacting with strong reducing agents, for example:
SO 2 + 2CO \u003d S + 2CO 2 (at 500 ° C, in the presence of Al 2 O 3);
SO 2 + 2H 2 \u003d S + 2H 2 O.
Production of sulfur oxide (IV)
Burning sulfur in air
S + O 2 \u003d SO 2.
Sulfide oxidation
4FeS 2 + 11O 2 \u003d 2Fe 2 O 3 + 8SO 2.
The action of strong acids on metal sulfites
Na 2 SO 3 + 2H 2 SO 4 \u003d 2NaHSO 4 + H 2 O + SO 2.
1.11.2. Sulfuric acid and its salts
When sulfur dioxide is dissolved in water, weak sulfurous acid is formed, the bulk of the dissolved SO 2 is in the form of a hydrated form of SO 2 H 2 O, a crystalline hydrate is also released upon cooling, only a small part of the sulfurous acid molecules dissociates into sulfite and hydrosulfite ions. In the free state, the acid is not isolated.
Being dibasic, it forms two types of salts: medium - sulfites and acidic - hydrosulfites. Only alkali metal sulfites and hydrosulfites of alkali and alkaline earth metals dissolve in water.
DEFINITION
Sulphur dioxide(sulfur oxide (IV), sulfur dioxide) under normal conditions is a colorless gas with a characteristic pungent odor (melting point is (-75.5 o C), boiling - (-10.1 o C).
The solubility of sulfur oxide (IV) in water is very high (under normal conditions, about 40 volumes of SO 2 per volume of water). An aqueous solution of sulfur dioxide is called sulfurous acid.
Chemical formula of sulfur dioxide
Chemical formula of sulfur dioxide- SO 2 . It shows that the molecule of this complex substance contains one sulfur atom (Ar = 32 a.m.u.) and two oxygen atoms (Ar = 16 a.m.u.). According to the chemical formula, you can calculate the molecular weight of sulfur dioxide:
Mr(SO 2) \u003d Ar (S) + 2 × Ar (O) \u003d 32 + 2 × 16 \u003d 32 + 32 \u003d 64
Structural (graphical) formula of sulfur dioxide
More illustrative is structural (graphical) formula of sulfur dioxide. It shows how atoms are connected to each other within a molecule. The structure of the SO 2 molecule (Fig. 1) is similar to the structure of the ozone O 3 (OO 2) molecule, but the molecule is highly thermally stable.
Rice. 1. The structure of the sulfur dioxide molecule, indicating the bond angles between bonds and the lengths of chemical bonds.
Showing the distribution of electrons in an atom by energy sublevels, it is customary to depict only for individual chemical elements, however, for sulfur dioxide, the following formula can also be presented:
Examples of problem solving
EXAMPLE 1
| Exercise | The composition of the substance includes 32.5% sodium, 22.5% sulfur and 45% oxygen. Derive the chemical formula of the substance. |
| Solution | The mass fraction of the element X in the molecule of the HX composition is calculated by the following formula: ω (X) = n × Ar (X) / M (HX) × 100% Let us denote the number of moles of elements that make up the compound as "x" (sodium), "y" (sulfur) and "z" (oxygen). Then, the molar ratio will look like this (the values of relative atomic masses taken from the Periodic Table of D.I. Mendeleev will be rounded to integers): x:y:z = ω(Na)/Ar(Na) : ω(S)/Ar(S) : ω(O)/Ar(O); x:y:z= 32.5/23: 22.5/32: 45/16; x:y:z= 1.4: 0.7: 2.8 = 2: 1: 4 So the formula for the compound of sodium, sulfur and oxygen will look like Na 2 SO 4. It's sodium sulfate. |
| Answer | Na2SO4 |
EXAMPLE 2
| Exercise | Magnesium combines with nitrogen, forming magnesium nitride, in a mass ratio of 18:7. Derive the compound formula. |
| Solution | In order to find out what kind of relationship chemical elements in the composition of the molecule, it is necessary to find their amount of substance. It is known that to find the amount of a substance, the formula should be used: Let's find the molar masses of magnesium and nitrogen (the values of the relative atomic masses taken from the Periodic Table of D.I. Mendeleev will be rounded up to whole numbers). It is known that M = Mr, which means M(Mg) = 24 g/mol, and M(N) = 14 g/mol. Then, the amount of substance of these elements is equal to: n (Mg) = m (Mg) / M (Mg); n (Mg) \u003d 18 / 24 \u003d 0.75 mol n(N) = m(N) / M(N); n(N) = 7 / 14 = 0.5 mol Find the molar ratio: n(Mg) :n(N) = 0.75: 0.5 = 1.5:1 = 3:2, those. the formula for the compound of magnesium with nitrogen is Mg 3 N 2. |
| Answer | Mg3N2 |
Sulfur dioxide has a molecular structure similar to ozone. The sulfur atom in the center of the molecule is bonded to two oxygen atoms. This gaseous product of sulfur oxidation is colorless, emits a pungent odor, easily condenses into a clear liquid under changing conditions. The substance is highly soluble in water, has antiseptic properties. SO 2 is obtained in large quantities in the chemical industry, namely in the cycle of sulfuric acid production. The gas is widely used for processing agricultural and food products, bleaching fabrics in the textile industry.
Systematic and trivial names of substances
It is necessary to understand the variety of terms related to the same compound. The official name of the compound, chemical composition which reflects the formula SO 2 - sulfur dioxide. IUPAC recommends the use of this term and its English equivalent, Sulfur dioxide. Textbooks for schools and universities often mention another name - sulfur oxide (IV). The Roman numeral in brackets denotes the valency of the S atom. The oxygen in this oxide is bivalent, and oxidation number sulfur +4. The technical literature uses obsolete terms such as sulphur dioxide, anhydride of sulfurous acid (a product of its dehydration).
Composition and features of the molecular structure of SO 2
The SO 2 molecule is formed by one sulfur atom and two oxygen atoms. There is an angle of 120° between covalent bonds. In the sulfur atom, sp2 hybridization occurs - the clouds of one s and two p electrons are aligned in shape and energy. They are involved in the formation of a covalent bond between sulfur and oxygen. In the O–S pair, the distance between the atoms is 0.143 nm. Oxygen is more electronegative than sulfur, which means that the bonding pairs of electrons move from the center to the outer corners. The whole molecule is also polarized, the negative pole is the O atoms, the positive one is the S atom.
Some physical parameters of sulfur dioxide
Quadrivalent sulfur oxide at normal rates environment retains a gaseous state of aggregation. The formula for sulfur dioxide allows you to determine its relative molecular and molar masses: Mr (SO 2) \u003d 64.066, M \u003d 64.066 g / mol (can be rounded up to 64 g / mol). This gas is almost 2.3 times heavier than air (M(air) = 29 g/mol). Dioxide has a sharp specific smell of burning sulfur, which is difficult to confuse with any other. It is unpleasant, irritates the mucous membranes of the eyes, causes a cough. But sulfur oxide (IV) is not as toxic as hydrogen sulfide.
Under pressure at room temperature, gaseous sulfur dioxide liquefies. At low temperatures, the substance is in a solid state, melts at -72 ... -75.5 ° C. With a further increase in temperature, a liquid appears, and at -10.1 ° C, gas is again formed. SO 2 molecules are thermally stable, decomposition into atomic sulfur and molecular oxygen occurs at very high temperatures (about 2800 ºС).
Solubility and interaction with water
Sulfur dioxide, when dissolved in water, partially interacts with it to form a very weak sulfurous acid. At the time of receipt, it immediately decomposes into anhydride and water: SO 2 + H 2 O ↔ H 2 SO 3. In fact, it is not sulfurous acid that is present in the solution, but hydrated SO 2 molecules. Gaseous dioxide interacts better with cool water, its solubility decreases with increasing temperature. Under normal conditions, it can dissolve in 1 volume of water up to 40 volumes of gas.
Sulfur dioxide in nature
Significant volumes of sulfur dioxide are released with volcanic gases and lava during eruptions. Many human activities also increase the concentration of SO 2 in the atmosphere.
Sulfur dioxide is supplied to the air by metallurgical plants, where exhaust gases are not captured during the roasting of ore. Many types of fossil fuels contain sulfur, as a result, significant amounts of sulfur dioxide are released into the atmospheric air during the combustion of coal, oil, gas, and the fuel obtained from them. Sulfur dioxide becomes toxic to humans at concentrations in the air above 0.03%. A person begins shortness of breath, there may be phenomena resembling bronchitis and pneumonia. A very high concentration of sulfur dioxide in the atmosphere can lead to severe poisoning or death.
Sulfur dioxide - production in the laboratory and in industry
Laboratory methods:
- When sulfur is burned in a flask with oxygen or air, dioxide is obtained according to the formula: S + O 2 \u003d SO 2.
- You can act on the salts of sulfurous acid with stronger inorganic acids, it is better to take hydrochloric, but you can dilute sulfuric:
- Na 2 SO 3 + 2HCl \u003d 2NaCl + H 2 SO 3;
- Na 2 SO 3 + H 2 SO 4 (diff.) \u003d Na 2 SO 4 + H 2 SO 3;
- H 2 SO 3 \u003d H 2 O + SO 2.
3. When copper interacts with concentrated sulfuric acid, not hydrogen is released, but sulfur dioxide:
2H 2 SO 4 (conc.) + Cu \u003d CuSO 4 + 2H 2 O + SO 2.
Modern ways industrial production of sulfur dioxide:
- Oxidation of natural sulfur during its combustion in special furnaces: S + O 2 = SO 2.
- Roasting iron pyrite (pyrite).
Basic chemical properties of sulfur dioxide
Sulfur dioxide is a chemically active compound. In redox processes, this substance often acts as a reducing agent. For example, when molecular bromine interacts with sulfur dioxide, the reaction products are sulfuric acid and hydrogen bromide. The oxidizing properties of SO 2 are manifested if this gas is passed through hydrogen sulfide water. As a result, sulfur is released, self-oxidation-self-healing occurs: SO 2 + 2H 2 S \u003d 3S + 2H 2 O.
Sulfur dioxide exhibits acidic properties. It corresponds to one of the weakest and most unstable acids - sulfurous. This compound does not exist in its pure form; it is possible to detect the acidic properties of a sulfur dioxide solution using indicators (litmus turns pink). Sulfurous acid gives medium salts - sulfites and acidic - hydrosulfites. Among them are stable compounds.
The process of oxidation of sulfur in dioxide to a hexavalent state in sulfuric anhydride is catalytic. The resulting substance dissolves vigorously in water, reacts with H 2 O molecules. The reaction is exothermic, sulfuric acid is formed, or rather, its hydrated form.
Practical use of sour gas
The main process for the industrial production of sulfuric acid, which requires element dioxide, has four stages:
- Obtaining sulfur dioxide by burning sulfur in special furnaces.
- Purification of the resulting sulfur dioxide from all kinds of impurities.
- Further oxidation to hexavalent sulfur in the presence of a catalyst.
- Absorption of sulfur trioxide by water.
In the past, almost all of the sulfur dioxide needed for commercial production of sulfuric acid came from the roasting of pyrite as a by-product of steelmaking. New types of processing of metallurgical raw materials use less ore combustion. Therefore, the main starting material for sulfuric acid production in last years became natural sulfur. Significant world reserves of this raw material, its availability make it possible to organize large-scale processing.
Sulfur dioxide is widely used not only in the chemical industry, but also in other sectors of the economy. Textile mills use this substance and the products of its chemical interaction to bleach silk and woolen fabrics. This is one of the types of chlorine-free bleaching, in which the fibers are not destroyed.
Sulfur dioxide has excellent disinfectant properties, which is used in the fight against fungi and bacteria. Sulfur dioxide is used to fumigate agricultural storages, wine barrels and cellars. SO 2 is used in the food industry as a preservative and antibacterial agent. Add it to syrups, soak fresh fruits in it. Sulfitization
sugar beet juice discolors and disinfects raw materials. Canned vegetable purees and juices also contain sulfur dioxide as an antioxidant and preservative agent.
Hydrogen sulfide - H2S
Sulfur compounds -2, +4, +6. Qualitative reactions to sulfides, sulfites, sulfates.
Interaction Receive:
1. hydrogen with sulfur at t - 300 0
2. when acting on sulfides of mineral acids:
Na 2 S + 2HCl \u003d 2 NaCl + H 2 S
colorless gas, with the smell of rotten eggs, poisonous, heavier than air, dissolving in water, forms a weak hydrogen sulfide acid.
Acid-base properties
1. A solution of hydrogen sulfide in water - hydrosulfide acid - is a weak dibasic acid, therefore it dissociates in steps:
H 2 S ↔ HS - + H +
HS - ↔ H - + S 2-
2. Hydrosulfuric acid has the general properties of acids, reacts with metals, basic oxides, bases, salts:
H 2 S + Ca \u003d CaS + H 2
H 2 S + CaO \u003d CaS + H 2 O
H 2 S + 2NaOH \u003d Na 2 S + 2H 2 O
H 2 S + CuSO 4 \u003d CuS ↓ + H 2 SO 4
All acidic salts - hydrosulfides - are highly soluble in water. Normal salts - sulfides - dissolve in water in different ways: sulfides of alkali and alkaline earth metals are highly soluble, sulfides of other metals are insoluble in water, and sulfides of copper, lead, mercury and some other heavy metals do not dissolve even in acids (except nitric acid)
CuS + 4HNO 3 \u003d Cu (NO 3) 2 + 3S + 2NO + 2H 2 O
Soluble sulfides undergo hydrolysis - at the anion.
Na 2 S ↔ 2Na + + S 2-
S 2- +HOH ↔HS - +OH -
Na 2 S + H 2 O ↔ NaHS + NaOH
A qualitative reaction to hydrosulfide acid and its soluble salts (i.e., to the sulfide ion S 2-) is their interaction with soluble lead salts, resulting in a black PbS precipitate
Na 2 S + Pb (NO 3) 2 \u003d 2NaNO 3 + PbS ↓
Pb 2+ + S 2- = PbS↓
Shows only restorative properties, tk. the sulfur atom has the lowest oxidation state -2
1. with oxygen
a) lacking
2H 2 S -2 + O 2 0 \u003d S 0 + 2H 2 O -2
b) with excess oxygen
2H 2 S + 3O 2 \u003d 2SO 2 + 2H 2 O
2. with halogens (discoloration of bromine water)
H 2 S -2 + Br 2 \u003d S 0 + 2HBr -1
3. with conc. HNO3
H 2 S + 2HNO 3 (k) \u003d S + 2NO 2 + 2H 2 O
b) with strong oxidizing agents (KMnO 4, K 2 CrO 4 in an acidic environment)
2KMnO 4 + 3H 2 SO 4 + 5H 2 S \u003d 5S + 2MnSO 4 + K 2 SO 4 + 8H 2 O
c) hydrosulfide acid is oxidized not only by strong oxidizing agents, but also by weaker ones, for example, iron (III) salts, sulfurous acid, etc.
2FeCl 3 + H 2 S = 2FeCl 2 + S + 2HCl
H 2 SO 3 + 2H 2 S \u003d 3S + 3H 2 O
Receipt
1. combustion of sulfur in oxygen.
2. combustion of hydrogen sulfide in excess O 2
2H 2 S + 3O 2 \u003d 2SO 2 + 2H 2 O
3. sulfide oxidation
2CuS + 3O 2 \u003d 2SO 2 + 2CuO
4. interaction of sulfites with acids
Na 2 SO 3 + H 2 SO 4 \u003d Na 2 SO 4 + SO 2 + H 2 O
5. interaction of metals in a series of activities after (H 2) with conc. H2SO4
Cu + 2H 2 SO 4 \u003d CuSO 4 + SO 2 + 2H 2 O
Physical Properties
Gas, colorless, with a suffocating smell of burnt sulfur, poisonous, more than 2 times heavier than air, highly soluble in water (at room temperature, about 40 volumes of gas dissolve in one volume).
Chemical properties:
Acid-base properties
SO 2 is a typical acidic oxide.
1.with alkalis, forming two types of salts: sulfites and hydrosulfites
2KOH + SO 2 \u003d K 2 SO 3 + H 2 O
KOH + SO 2 \u003d KHSO 3 + H 2 O
2.with basic oxides
K 2 O + SO 2 \u003d K 2 SO 3
3. weak sulfurous acid is formed with water
H 2 O + SO 2 \u003d H 2 SO 3
Sulfurous acid exists only in solution, is a weak acid,
has all the common properties of acids.
4. qualitative reaction to sulfite - ion - SO 3 2 - action of mineral acids
Na 2 SO 3 + 2HCl \u003d 2Na 2 Cl + SO 2 + H 2 O smell of burnt sulfur
redox properties
In OVR, it can be both an oxidizing agent and a reducing agent, because the sulfur atom in SO 2 has an intermediate oxidation state of +4.
As an oxidizing agent:
SO 2 + 2H 2 S = 3S + 2H 2 S
As a restorer:
2SO 2 +O 2 \u003d 2SO 3
Cl 2 + SO 2 + 2H 2 O \u003d H 2 SO 4 + 2HCl
2KMnO 4 + 5SO 2 + 2H 2 O \u003d K 2 SO 4 + 2H 2 SO 4 + 2MnSO 4
Sulfur oxide (VI) SO 3 (sulfuric anhydride)
Receipt:
Sulfur dioxide oxidation
2SO 2 + O 2 = 2SO 3 ( t 0 , cat)
Physical Properties
A colorless liquid, at temperatures below 17 0 С it turns into a white crystalline mass. Thermally unstable compound, completely decomposes at 700 0 C. It is highly soluble in water, in anhydrous sulfuric acid and reacts with it to form oleum
SO 3 + H 2 SO 4 \u003d H 2 S 2 O 7
Chemical properties
Acid-base properties
A typical acidic oxide.
1.with alkalis, forming two types of salts: sulfates and hydrosulfates
2KOH + SO 3 \u003d K 2 SO 4 + H 2 O
KOH + SO 3 \u003d KHSO 4 + H 2 O
2.with basic oxides
CaO + SO 2 \u003d CaSO 4
3. with water
H 2 O + SO 3 \u003d H 2 SO 4
redox properties
Sulfur oxide (VI) - a strong oxidizing agent, usually reduced to SO 2
3SO 3 + H 2 S \u003d 4SO 2 + H 2 O
Sulfuric acid H 2 SO 4
Getting sulfuric acid
In industry, acid is produced by the contact method:
1. pyrite firing
4FeS 2 + 11O 2 \u003d 2Fe 2 O 3 + 8SO 2
2. oxidation of SO 2 to SO 3
2SO 2 + O 2 = 2SO 3 ( t 0 , cat)
3. dissolution of SO 3 in sulfuric acid
n SO 3 + H 2 SO 4 \u003d H 2 SO 4 ∙ n SO 3 (oleum)
H 2 SO 4 ∙ n SO 3 + H 2 O \u003d H 2 SO 4
Physical Properties
H 2 SO 4 is a heavy oily liquid, odorless and colorless, hygroscopic. It is miscible with water in any ratio, when concentrated sulfuric acid is dissolved in water, a large amount of heat is released, so it must be carefully poured into water, and not vice versa (first water, then acid, otherwise big trouble will happen)
A solution of sulfuric acid in water with an H 2 SO 4 content of less than 70% is usually called dilute sulfuric acid, more than 70% is concentrated.
Chemical properties
Acid-base
Dilute sulfuric acid exhibits all the characteristic properties of strong acids. Dissociates in aqueous solution:
H 2 SO 4 ↔ 2H + + SO 4 2-
1. with basic oxides
MgO + H 2 SO 4 \u003d MgSO 4 + H 2 O
2. with bases
2NaOH + H 2 SO 4 \u003d Na 2 SO 4 + 2H 2 O
3. with salts
BaCl 2 + H 2 SO 4 \u003d BaSO 4 ↓ + 2HCl
Ba 2+ + SO 4 2- = BaSO 4 ↓ (white precipitate)
Qualitative reaction to the sulfate ion SO 4 2-
Due to the higher boiling point, compared to other acids, sulfuric acid displaces them from salts when heated:
NaCl + H 2 SO 4 \u003d HCl + NaHSO 4
redox properties
In dilute H 2 SO 4, oxidizing agents are H + ions, and in concentrated H 2 SO 4 - sulfate ions SO 4 2
In dilute sulfuric acid, metals that are in the order of activity up to hydrogen dissolve, while sulfates are formed and hydrogen is released
Zn + H 2 SO 4 \u003d ZnSO 4 + H 2
Concentrated sulfuric acid is a vigorous oxidizing agent, especially when heated. It oxidizes many metals, non-metals, inorganic and organic substances.
H 2 SO 4 (to) oxidizing agent S +6
With more active metals, sulfuric acid, depending on the concentration, can be reduced to a variety of products.
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 = 4ZnSO 4 + H 2 S + 4H 2 O
Concentrated sulfuric acid oxidizes some non-metals (sulfur, carbon, phosphorus, etc.), reducing to sulfur oxide (IV)
S + 2H 2 SO 4 \u003d 3SO 2 + 2H 2 O
C + 2H 2 SO 4 \u003d 2SO 2 + CO 2 + 2H 2 O
Interaction with some complex substances
H 2 SO 4 + 8HI \u003d 4I 2 + H 2 S + 4 H 2 O
H 2 SO 4 + 2HBr \u003d Br 2 + SO 2 + 2H 2 O
Salts of sulfuric acid
2 types of salts: sulfates and hydrosulfates
Salts of sulfuric acid have all the common properties of salts. Their relation to heating is special. Sulfates of active metals (Na, K, Ba) do not decompose even when heated above 1000 0 C, salts of less active metals (Al, Fe, Cu) decompose even with slight heating
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