Comparative characteristics of the elements of the subgroup iva. General characteristics of the elements of the IVA group. The most important carbon compounds

Lecture 8

TOPIC : Group elements IVA.

Carbon

Questions studied at the lecture:

1. IVA group.
2. Carbon. General characteristics of carbon.
3. Chemical properties of carbon.
4. The most important compounds of carbon.

General characteristics of the elements IVA group

To the elements of the main subgroup IV groups belong C, Si, Ge, Sn, P in. Electronic formula of the outer valence level nS 2 np 2 , that is, they have 4 valence electrons and these are p elements, therefore they are in the main subgroup IV group.

││││

│↓│np

In the ground state of an atom, two electrons are paired and two are unpaired. The outer shell of carbon has 2 electrons, silicon has 8, and Ge, Sn, P c – 18 electrons each. That's why Ge, Sn, P in are combined into a germanium subgroup (these are complete electronic analogues).

In this subgroup of p-elements, as in other subgroups of p-elements, the properties of atoms of elements change periodically:

Table 9

Thus, from top to bottom in the subgroup, the radius of the atom increases, so the ionization energy decreases, so the ability to donate electrons increases, and the tendency to complete the outer electron shell to an octet decreases sharply, so from C to Pb, reducing properties and metallic properties increase, and non-metallic properties decrease . Carbon and silicon are typical non-metals, Ge metallic properties are already appearing and in appearance it looks like a metal, although it is a semiconductor. With tin, metallic properties already predominate, and lead is a typical metal.

Having 4 valence electrons, atoms in their compounds can show oxidation states from the minimum (-4) to the maximum (+4), and they are characterized by even S.O.: -4, 0, +2, +4; S.O. = -4 is typical for C and Si with metals.

The nature of the relationship with other elements.Carbon forms only covalent bonds, silicon also predominantly forms covalent bonds. For tin and lead, especially in S.O. = +2, the ionic nature of the bond is more characteristic (for example, Рв( NO 3 ) 2 ).

covalence determined by the valence structure of the atom. The carbon atom has 4 valence orbitals and the maximum covalence is 4. For other elements, the covalence can be greater than four, since there is a valence d sublevel (for example, H 2 [SiF 6 ]).

Hybridization . The type of hybridization is determined by the type and number of valence orbitals. Carbon has only S - and p-valence orbitals, so it can be Sp (carbine, CO 2 , CS 2 ), Sp 2 (graphite, benzene, COCl 2 ), Sp 3 hybridization (CH 4 , diamond, CCl 4 ). For silicon, the most characteristic Sp 3 - hybridization (SiO 2, SiCl 4 ), but it has a valence d -sublevel, so there is also Sp 3 d 2 - hybridization, for example, H 2 [SiF 6 ].

IV the PSE group is the middle of the table of D.I. Mendeleev. Here, a sharp change in properties from non-metals to metals is clearly seen. We will separately consider carbon, then silicon, then elements of the germanium subgroup.

Carbon. General characteristics of carbon

The carbon content in the earth's crust is low (about 0.1% mass). Most of it is contained in the composition of sparingly soluble carbonates (CaCO 3 , MgCO 3 ), oil, coal, natural gas. CO content 2 in the air is small (0.03%), but its total mass is approximately 600 million tons. Carbon is part of the tissues of all living organisms (the main component of the plant and animal world). Carbon is also found in the free state, mainly in the form of graphite and diamond.

In nature, carbon is known as two stable isotopes: 12 C (98.892%) and 13 C (1.108%). Under the influence of cosmic rays, a certain amount of β-radioactive isotope is also formed in the atmosphere 14 FROM: . By content 14 With in plant residues, their age is judged. Radioactive isotopes with mass numbers from 10 to 16 have also been obtained.

Unlike F 2, N 2, O 2 simple substances of carbon have a polymeric structure. In accordance with the characteristic types of hybridization of valence orbitals, C atoms can combine into polymeric formations of a three-dimensional modification (diamond, sp 3 ), two-dimensional or layered modification (graphite, Sp 2 ) and a linear polymer (carbine, sp).

Chemical properties of carbon

Chemically, carbon is very inert. But when heated, it is able to interact with many metals and non-metals, while exhibiting both oxidizing and reducing properties.

Diamond + 2 F 2 → CF 4 , and graphite forms graphite fluoride CF

(and then + F 2 → CF 4 ). One of the methods for separating diamond from graphite is based on a different attitude towards fluorine. Carbon does not react with other halogens. With oxygen (O 2 ) carbon with a lack of oxygen forms CO, with an excess of oxygen forms CO 2 .

2C + O 2 → 2CO; C + O 2 → CO 2.

At high temperatures, carbon reacts with metals to form metal carbides:

Ca + 2C \u003d CaC 2.

When heated, it reacts with hydrogen, sulfur, silicon:

t o t o

C + 2 H 2 \u003d CH 4 C + 2S ↔ CS 2

C + Si = SiC.

Carbon also reacts with complex substances. When water vapor is passed through heated coal, a mixture of CO and H is formed. 2 - water gas (at a temperature of more than 1200 about C):

C + HOH \u003d CO + H 2.

This mixture is widely used as a gaseous fuel.

At high temperatures, carbon is able to reduce many metals from their oxides, which is widely used in metallurgy.

ZnO + C → Zn + CO

The most important carbon compounds

1. metal carbides.

Since it is common for carbon to form homochains, the composition of most carbides does not correspond to the oxidation state of carbon equal to (-4). According to the type of chemical bond, covalent, ionic-covalent and metal carbides are distinguished. In most cases, carbides are obtained by strong heating of the corresponding simple substances or their oxides with carbon

T o t o

V 2 O 5 + 7C → 2VC + 5CO; Ca + 2 C → CaC 2.

In this case, carbides of different composition are obtained.

Salt-like or ion-covalent carbides are compounds of active and some other metals: Be 2 C, CaC 2, Al 4 C 3, Mn 3 C . In these compounds, the chemical bond is intermediate between ionic and covalent. Under the action of water or dilute acids, they are hydrolyzed and hydroxides and the corresponding hydrocarbons are obtained:

CaC 2 + 2HON → Ca (OH) 2 + C 2 H 2;

Al 4 C 3 + 12HOH → 4Al(OH) 3 + 3CH 4 .

In metal carbides, carbon atoms occupy octahedral voids in the structures of metals (side subgroups IV - VIII groups). These are very hard, refractory and heat-resistant substances, many of them exhibit metallic properties: high electrical conductivity, metallic luster. The composition of such carbides varies over a wide range. Thus, titanium carbides have the composition TiC 0.6 - 1.0 .

Covalent carbides - SiC and B 4 C. They are polymeric. The chemical bond in them approaches a purely covalent bond, since boron and silicon are neighbors of carbon in PSC and are close to it in terms of the radius of the atom and OEO. They are very hard and chemically inert. Methane CH can also be considered as the simplest covalent carbide. 4 .

1. Carbon halides

Carbon forms many compounds with halogens, the simplest of which have the formula C H al 4 , i.e. carbon tetrahalides. In them S.O. carbon is +4, sp 3 -hybridization of the C atom, so the molecules C Н al 4 - tetrahedra. CF 4 - gas, CCl 4 - liquid, CBr 4 and CJ 4 - solids. Only CF4 obtained directly from F2 and C, carbon does not react with other halogens. Carbon tetrachloride is obtained by chlorination of carbon disulfide:

CS 2 + 3Cl 2 \u003d CCl 4 + S 2 Cl 2.

All C H al 4 insoluble in water, but soluble in organic solvents.

t o , Kat

C H al 4 (g) + 2HON (g) \u003d CO 2 + 4HNa l (d) (hydrolysis occurs with strong heating and in the presence of a catalyst). Of practical importance CF 4 , SS l 4 .

CF4 , as well as other fluorinated carbon compounds, for example CF2Cl2 (difluorodichloromethane) is used as freons - working substances of refrigeration machines.

CCl 4 used as a non-flammable solvent for organic substances (fats, oils, resins), as well as liquid for fire extinguishers.

1. Carbon monoxide (P).

Carbon monoxide (P) CO is a colorless, odorless gas, slightly soluble in water. Very toxic (carbon monoxide): blood hemoglobin associated with CO loses its ability to combine with O 2 and be its carrier.

Carbon monoxide (P) is obtained:

• with incomplete oxidation of carbon 2C + O 2 = 2CO;

• in industry, they are obtained by the reaction: CO 2 + C = 2CO;
• when passing superheated water vapor over hot coal:

C + HOH \u003d CO + H 2 t o

• decomposition of carbonyls Fe (CO) 5 → Fe + 5 CO;
• in the laboratory, CO is obtained by acting on formic acid with water-removing substances ( H 2 SO 4, P 2 O 5):

HCOOH → CO + HOH.

However, CO is not anhydride of formic acid, since in CO carbon is trivalent, and in HCOOH it is tetravalent. Thus, CO is a non-salt-forming oxide.

The solubility of CO in water is low and no chemical reaction occurs. In the CO molecule, as in the molecule N 2 - triple bond. According to the method of valence bonds, 2 bonds are formed due to the pairing of two unpaired p - electrons C and O (of each atom), and the third - according to the donor-acceptor mechanism due to the free 2p - orbital of the C atom and 2p - electron pair of the oxygen atom: C ≡ O The CO triple bond is very strong and its energy is very large (1066 kJ / mol) - more than in N 2 . For carbon monoxide (P), the following three types of reactions are characteristic:

1. oxidation reactions. CO is a strong reducing agent, however, due to the strong triple bond in the molecule, redox reactions involving CO proceed quickly only at high temperatures. The reduction of oxides with the help of CO during heating is of great importance in metallurgy.

Fe 2 O 3 + 3CO = 3CO 2 + 2Fe.

CO can be oxidized by oxygen: t o

2CO + O 2 \u003d 2CO 2.

1. another characteristic chemical property of CO is the tendency toaddition reactions, which is due to the valence unsaturation of carbon in CO (in these reactions, carbon passes into a tetravalent state, which is more characteristic of it than the trivalence of carbon in CO).

So, CO reacts with chlorine to form phosgene COC l2 :

CO + Cl 2 \u003d COCl 2 (in this reaction, CO is also a reducing agent). The reaction is accelerated by the action of light and a catalyst. Phosgene is a brown gas, very poisonous - a strong toxic substance. Slowly hydrolyzes COCl 2 + 2 HOH → 2 HCl + H 2 CO 3.

Phosgene is used in the synthesis of various substances and was used in the First World War as a chemical warfare agent.

When heated, CO reacts with sulfur to form carbon sulfoxide COS :

CO + S = COS (gas).

When heated under pressure, CO reacts with hydrogen to form methanol

t o , p

CO + 2H 2 ↔ CH 3 OH.

Synthesis of methanol from CO and H 2 is one of the most important chemical industries.

1. unlike most other carbon compounds, the CO molecule has an unshared electron pair at the C atom. Therefore, the CO molecule can act ligand in various complexes. Particularly numerous are the products of addition of CO to metal atoms, which are called carbonyls. About 1000 carbonyls are known, including carbonyls containing other ligands besides CO. Carbonyls (complexes) receive:

T, p t, p

Fe + 5CO → Ni + 4CO → .

There are gaseous, liquid and solid carbonyls, in which the metal has an oxidation state of 0. When heated, the carbonyls decompose and powdered metals of a very high degree of purity are obtained:

t o

Ni(CO) 4 → Ni + 4CO.

Carbonyls are used in syntheses and to obtain highly pure metals. All carbonyls, like CO, are extremely toxic.

1. Carbon monoxide (IV).

CO 2 molecule has a linear structure (O = C = O), Sp - hybridization of the carbon atom. Two σ-type bonds arise due to the overlap of two Sp – hybrid orbitals of the C atom and two 2р X - orbitals of two oxygen atoms, on which unpaired electrons. Two other π-type bonds arise when overlapping 2p y - and 2p z - orbitals of the C atom (non-hybrid) with the corresponding 2p y - and 2p z - orbitals of oxygen atoms.

Obtaining CO 2:

- in industryobtained by roasting limestone

CaCO 3 → CaO + CO 2;

In the laboratory obtained in the Kipp apparatus according to the reaction

CaCO 3 + 2HCl → CaCl 2 + CO 2 + HOH.

Physical properties of CO 2 : it is a gas, heavier than air, solubility in water is low (at 0 about C in 1 liter of water dissolves 1.7 liters of CO 2, and at 15 o C dissolves 1 liter of CO 2 ), while some of the dissolved CO 2 reacts with water to form carbonic acid:

HOH + CO 2 ↔ H 2 CO 3 . The equilibrium is shifted to the left (←), so most of the dissolved CO 2 in the form of CO 2 and not acid.

AT chemically CO 2 exhibits: a) the properties of an acid oxide and when interacting with alkali solutions, carbonates are formed, and with an excess of CO 2 - hydrocarbons:

2NaOH + CO 2 → Na 2 CO 3 + H 2 O NaOH + CO 2 → NaHCO 3.

b) oxidizing properties, but oxidizing properties CO2 are very weak, since S.O. = +4 is the most characteristic oxidation state of carbon. At the same time, CO 2 reduced to CO or C:

C + CO 2 ↔ 2CO.

C O 2 used in the production of soda, for extinguishing fires, preparing mineral water, as an inert medium in syntheses.

1. Carbonic acid and its salts

Carbonic acid is known only in dilute aqueous solutions. Formed by the interaction of CO 2 with water. In an aqueous solution, most of the dissolved CO 2 in the hydrated state and only a small part in the form of H 2 CO 3, HCO 3 -, CO 3 2- , that is, equilibrium is established in an aqueous solution:

CO 2 + HOH ↔ H 2 CO 3 ↔ H + + HCO 3 - ↔ 2H + + CO 3 2-.

The equilibrium is strongly shifted to the left (←) and its position depends on temperature, environment, etc.

Carbonic acid is considered a weak acid (K 1 = 4,2 ∙ 10 -7 ). This is the apparent ionization constant K and he. , it is related to the total amount of CO dissolved in water 2 , and not to the true concentration of carbonic acid, which is not exactly known. But since the molecules H 2 CO 3 in solution is small, then the true K and he. carbonic acid is much more than indicated above. So, apparently, the true value of K 1 ≈ 10 -4 , that is, carbonic acid is an acid of medium strength.

Salts (carbonates) are usually slightly soluble in water. Carbonates dissolve well+ , Na + , R в + , Cs + , Tl +1 , NH 4 + . Bicarbonates, unlike carbonates, are mostly soluble in water.

Salt hydrolysis: Na 2 CO 3 + HOH ↔ NaHCO 3 + NaOH (pH> 7).

When heated, carbonates decompose, forming metal oxide and CO 2 .The stronger the metallic properties of the element forming the cation, the more stable the carbonate. So, Na2CO3 melts without decomposition; CaCO 3 decomposes at 825 o C, and Ag 2 CO 3 decomposes at 100 about C. Bicarbonates decompose on slight heating:

2NaHCO 3 → Na 2 CO 3 + CO 2 + H 2 O.

1. Urea and carbon disulfide.

Urea or urea is obtained by the action of CO 2 for an aqueous solution H 3 N at 130 o C and 1∙10 7 Pa.

CO 2 + 2H 3 N \u003d CO (NH 2) 2 + H 2 O.

Urea is a white crystalline substance. It is used as a nitrogen fertilizer, for feeding livestock, for the production of plastics, pharmaceuticals (veronal, luminal).

Carbon disulphide (carbon disulfide) - CS2 under normal conditions - a volatile colorless liquid, poisonous. Clean CS2 It has a slight pleasant smell, but on contact with air it has a disgusting smell of its oxidation products. Carbon disulfide does not dissolve in water; when heated (150 about C) hydrolyzes to CO 2 and H 2 S :

CS 2 + 2HOH = CO 2 + 2H 2 S.

Carbon disulfide is easily oxidized and easily ignites in air with slight heating: CS 2 + 3 O 2 \u003d CO 2 + 2 SO 2.

Carbon disulfide is produced by the interaction of sulfur vapor with hot coal. Carbon disulfide is used as a good solvent for organic substances, phosphorus, sulfur, iodine. The bulk CS2 It is used to obtain viscose silk and as a means for combating pests in agriculture.

1. Hydrocyanic, thiocyanate and cyanic acids.

Hydrocyanic acid HCN (or hydrocyanic acid) has a linear structure, consists of 2 types of molecules in tautomeric equilibrium, which is shifted to the left at room temperature:

H - C ≡ N ↔ H - N ≡ C

cyanide isocyanide

hydrogen hydrogen

HCN - This is a volatile liquid with the smell of almonds, one of the strongest poisons, mixes with water in any ratio. in aqueous solution HCN - weak acid (K = 7.9 ∙ 10-10 ), which is much weaker than carbonic acid.

In industry HCN obtained by catalytic reaction:

t o , kat

CO + NH 3 → HCN + HOH.

Salts (cyanides) are obtained by reduction of carbonates with carbon when heated:

Na 2 CO 3 + C + 2NH 3 \u003d 2NaCN + 3H 2 O.

Hydrogen cyanide is used in organic synthesis, and NaCN and KCN - in the extraction of gold, for the production of complex cyanides, etc.

Cyanides are basic ( NaCN) and acid (JCN ). Hydrolysis of basic cyanide:

NaCN + HOH ↔ NaOH + HCN (pH > 7).

Hydrolysis of acidic cyanide produces two acids:

JCN + HOH = HJO + HCN.

cyanides d -elements do not dissolve in water, but due to complex formation they are easily dissolved in the presence of basic cyanides:

4KCN + Mn(CN) 2 = K 4 .

Complex cyanides are very stable.

Hydrogen thiocyanate HSCN or HNCS has a linear structure and consists of two types of molecules: H-S-C≡ NorH – N = C = S. In crystalline thiocyanateNaNCS, Ba(NCS) 2 the metal ion is located near the nitrogen atom; inAgSCN, hg(SCN) 2 metal ion - near the sulfur atom.

Rhodanides or thiocyanates are obtained by the action of sulfur on alkali metal cyanides (boiling solutions with sulfur):

to

KCN + S = KNCS.

Anhydrous hydrogen thiocyanate is obtained by heating lead (or mercury) thiocyanate in a currentH2 S:

to

Rv(SCN)2 + H2 S →RvS↓ + 2HNCS.

HNCS- a colorless oily liquid with a pungent odor, easily decomposed. It dissolves well in water, in an aqueous solutionHNCSforms a strong thiocyanate acid (K = 0.14). The rhodanides are mainly used in the dyeing of fabrics, andNH4 CNSused as an ion reagentFe3+ .

Also known are tautomeric cyanoic (HOCN) and isocyanic (HNCO) acids:

.

This equilibrium at room temperature is shifted to the left.

Salts - cyanates and isocyanates are obtained by oxidation of cyanides: 2KCN + O2 = 2 KOCN. Cyanic acid in aqueous solution is a medium strength acid.

The IVA group contains the most important elements, without which there would be neither us nor the Earth on which we live. This is carbon - the basis of all organic life, and silicon - the "monarch" of the mineral kingdom.

If carbon and silicon are typical non-metals, and tin and lead are metals, then germanium occupies an intermediate position. Some textbooks classify it as a non-metal, while others classify it as a metal. It is silvery white in color and looks like a metal, but has a diamond-like crystal lattice and is a semiconductor, like silicon.

From carbon to lead (with decreasing non-metallic properties):

w the stability of the negative oxidation state decreases (-4)

w the stability of the highest positive oxidation state decreases (+4)

w increases the stability of a low positive oxidation state (+2)

Carbon is the main constituent of all organisms. In nature, there are both simple substances formed by carbon (diamond, graphite) and compounds (carbon dioxide, various carbonates, methane and other hydrocarbons in the composition of natural gas and oil). The mass fraction of carbon in hard coal reaches 97%.
The carbon atom in the ground state can form two covalent bonds by the exchange mechanism, but such compounds are not formed under normal conditions. A carbon atom, going into an excited state, uses all four valence electrons.
Carbon forms quite a few allotropic modifications (see Fig. 16.2). These are diamond, graphite, carbine, various fullerenes.

In inorganic substances, the oxidation state of carbon is + II and + IV. There are two oxides with these oxidation states of carbon.
Carbon monoxide (II) is a colorless toxic gas, odorless. The trivial name is carbon monoxide. It is formed during the incomplete combustion of carbon-containing fuel. For the electronic structure of its molecule, see page 121. In terms of chemical properties, CO is a non-salt-forming oxide; when heated, it exhibits reducing properties (reduces many oxides of not very active metals to metal).
Carbon monoxide(IV) is a colorless, odorless gas. The trivial name is carbon dioxide. Acid oxide. It is slightly soluble in water (physically), partially reacts with it, forming carbonic acid H2CO3 (the molecules of this substance exist only in very dilute aqueous solutions).
Carbonic acid is a very weak dibasic acid that forms two series of salts (carbonates and bicarbonates). Most carbonates are insoluble in water. Of the bicarbonates, only alkali metal and ammonium bicarbonates exist as individual substances. Both the carbonate ion and the bicarbonate ion are particles of the base; therefore, both carbonates and bicarbonates in aqueous solutions undergo anion hydrolysis.
Of the carbonates, the most important are sodium carbonate Na2CO3 (soda, soda ash, washing soda), sodium bicarbonate NaHCO3 (baking soda, baking soda), potassium carbonate K2CO3 (potash) and calcium carbonate CaCO3 (chalk, marble, limestone).
Qualitative reaction to the presence of carbon dioxide in the gas mixture: the formation of a precipitate of calcium carbonate when the test gas is passed through lime water (saturated solution of calcium hydroxide) and the subsequent dissolution of the precipitate with further passing of the gas. Reactions taking place:

Ca2 + 2OH + CO2 = CaCO3 + H2O;
CaCO3 + CO2 + H2O = Ca2 + 2HCO3 .

In pharmacology and medicine, various carbon compounds are widely used - derivatives of carbonic acid and carboxylic acids, various heterocycles, polymers and other compounds. So, carbolene (activated carbon) is used to absorb and remove various toxins from the body; graphite (in the form of ointments) - for the treatment of skin diseases; radioactive isotopes of carbon - for scientific research (radiocarbon analysis).

Carbon is the basis of all organic substances. Every living organism is made up largely of carbon. Carbon is the basis of life. The source of carbon for living organisms is usually CO 2 from the atmosphere or water. As a result of photosynthesis, it enters biological food chains in which living things eat each other or each other's remains and thereby extract carbon to build their own body. The biological cycle of carbon ends either with oxidation and return to the atmosphere, or with disposal in the form of coal or oil.

Analytical reactions carbonate - ion CO 3 2-

Carbonates are salts of an unstable, very weak carbonic acid H 2 CO 3, which in the free state in aqueous solutions is unstable and decomposes with the release of CO 2: H 2 CO 3 - CO 2 + H 2 O

Ammonium, sodium, rubidium, cesium carbonates are soluble in water. Lithium carbonate is slightly soluble in water. Other metal carbonates are slightly soluble in water. Hydrocarbons dissolve in water. Carbonate - ions in aqueous solutions are colorless, undergo hydrolysis. Aqueous solutions of alkali metal bicarbonates do not stain when a drop of phenolphthalein solution is added to them, which makes it possible to distinguish carbonate solutions from bicarbonate solutions (pharmacopoeia test).

1. Reaction with barium chloride.

Ba 2+ + COz 2 - -> BaCO 3 (white fine crystalline)

Similar precipitates of carbonates give calcium cations (CaCO 3) and strontium (SrCO 3). The precipitate is soluble in mineral acids and in acetic acid. In a solution of H 2 SO 4 a white precipitate BaSO 4 is formed.

A solution of HC1 is slowly added dropwise to the precipitate until the precipitate is completely dissolved: BaCO3 + 2 HC1 -> BaC1 2 + CO 2 + H 2 O

2. Reaction with magnesium sulfate (pharmacopoeia).

Mg 2+ + CO3 2 - -> MgCO 3 (white)

Bicarbonate - HCO 3 ion - forms a precipitate of MgCO 3 with magnesium sulfate only when boiling: Mg 2+ + 2 HCO3- -> MgCO 3 + CO 2 + H 2 O

The precipitate of MgCO 3 dissolves in acids.

3. Reaction with mineral acids (pharmacopoeia).

CO 3 2- + 2 H 3 O \u003d H 2 CO 3 + 2H 2 O

HCO 3 - + H 3 O + = H 2 CO 3 + 2H 2 O

H 2 CO 3 -- CO 2 + H 2 O

Evolved gaseous CO 2 is detected by turbidity of baritone or lime water in a device for detecting gases, gas bubbles (CO 2), in a test tube - receiver - turbidity of the solution.

4. Reaction with uranyl hexacyanoferrate (II).

2CO 3 2 - + (UO 2) 2 (brown) -> 2 UO 2 CO 3 (colorless) + 4 -

A brown solution of uranyl hexacyanoferrate (II) is obtained by mixing a solution of uranyl acetate (CH 3 COO) 2 UO 2 with a solution of potassium hexacyanoferrate (II):

2(CH 3 COO) 2 GO 2 + K 4 -> (UO 2) 2 + 4 CH 3 COOK

To the resulting solution is added dropwise a solution of Na 2 CO 3 or K 2 CO 3 with stirring until the brown color disappears.

5. Separate discovery of carbonate - ions and bicarbonate - ions by reactions with calcium cations and ammonia.

If the solution simultaneously contains carbonate - ions and bicarbonate - ions, then each of them can be opened separately.

To do this, first, an excess of CaCl 2 solution is added to the analyzed solution. In this case, CO3 2 - is precipitated in the form of CaCO 3:

COz 2 - + Ca 2+ \u003d CaCO 3

Bicarbonate - ions remain in solution, since Ca (HCO 3) 2 solutions in water. The precipitate is separated from the solution and ammonia solution is added to the latter. HCO 2 - -anions with ammonia and calcium cations again precipitate CaCO 3: HCO s - + Ca 2+ + NH 3 -> CaCO3 + NH 4 +

6. Other reactions of the carbonate - ion.

Carbonate - ions when reacting with iron (III) chloride FeCl 3 form a brown precipitate Fe (OH) CO 3, with silver nitrate - a white precipitate of silver carbonate Ag 2 CO3, soluble in HbTO3 and decomposing when boiling in water to a dark precipitate Ag 2 O ISO 2: Ag 2 CO 3 -> Ag 2 O + CO 2

Analytical reactions of acetate - ion CH 3 COO "

Acetate - ion CH 3 COO- - anion of a weak monobasic acetic acid CH 3 COOH: colorless in aqueous solutions, undergoes hydrolysis, does not have redox properties; a fairly effective ligand and forms stable acetate complexes with many metal cations. When reacting with alcohols in an acidic medium, it gives esters.

Ammonium, alkali and most other metal acetates are highly soluble in water. Silver acetates CH 3 COOAg and mercury (I) are less soluble in water than acetates of other metals.

1. Reaction with iron (III) chloride (pharmacopoeia).

At pH = 5-8, the acetate - ion with Fe (III) cations forms a soluble dark red (strong tea color) acetate or iron (III) hydroxyacetate.

In aqueous solution, it is partially hydrolyzed; acidification of the solution with mineral acids inhibits hydrolysis and leads to the disappearance of the red color of the solution.

3 CH3COOH + Fe --> (CH 3 COO) 3 Fe + 3 H +

When boiling, a red-brown precipitate of basic iron acetate (III) precipitates from the solution:

(CH 3 COO) 3 Fe + 2 H 2 O<- Fe(OH) 2 CH 3 COO + 2 СН 3 СООН

Depending on the ratio of the concentrations of iron (III) and acetate ions, the composition of the precipitate may change and correspond, for example, to the formulas: Fe OH (CH 3 COO) 2, Fe 3 (OH) 2 O 3 (CH 3 COO), Fe 3 O (OH) (CH 3 COO) 6 or Fe 3 (OH) 2 (CH 3 COO) 7.

The reaction is interfered with by anions CO 3 2 -, SO 3 "-, PO 4 3 -, 4, which form precipitates with iron (III), as well as SCN- anions (giving red complexes with Fe 3+ cations), iodide - ion G, oxidizing to iodine 1 2, giving the solution a yellow color.

2. Reaction with sulfuric acid.

Acetate - an ion in a strongly acidic environment turns into weak acetic acid, the vapors of which have a characteristic smell of vinegar:

CH 3 COO- + H +<- СН 3 СООН

The reaction is hindered by anions NO 2 \ S 2 -, SO 3 2 -, S 2 O 3 2 -, which also emit gaseous products with a characteristic odor in a concentrated H 2 SO4 medium.

3. The reaction of the formation of acetic ethyl ether (pharmacopoeia).

The reaction is carried out in a sulfuric acid medium. With ethanol:

CH 3 COO- + H + -- CH 3 COOH CH 3 COOH + C 2 H 5 OH \u003d CH 3 COOS 2 H 4 + H 2 O

The released ethyl acetate is detected by a characteristic pleasant smell. Silver salts catalyze this reaction, so it is recommended to add a small amount of AgNO 3 during the reaction.

Similarly, when reacting with amyl alcohol C 5 HcOH, a pleasant-smelling amyl acetate CH 3 COOC 5 Ni (-pear-) is also formed. A characteristic smell of ethyl acetate is felt, which increases with careful heating of the mixture.

Analytical reactions tartrate - ROS ion - CH(OH) - CH(OH) - COMP. Tartrate ion - anion of a weak dibasic tartaric acid:

HO-CH-COOH

HO-CH-COOH

Tartrate - an ion is highly soluble in water. In aqueous solutions, tartrate ions are colorless, undergo hydrolysis, and are prone to complex formation, giving stable tartrate complexes with cations of many metals. Tartaric acid forms two series of salts - medium tartrates containing a two-charge tartrate - COCH (OH) CH (OH) COO - ion, and acid tartrates - hydro tartrates containing a singly charged hydro tartrate - HOOOCH (OH) CH (OH) COO - ion. Potassium hydrotartrate (-tartar-) KNS 4 H 4 O 6 is practically insoluble in water, which is used to open potassium cations. The average calcium salt is also slightly soluble in water. The average potassium salt K 2 C 4 H 4 O 6 is highly soluble in water.

I. Reaction with potassium chloride (pharmacopoeia).

C 4 H 4 O 6 2 - + K + + H + -> KNS 4 H 4 O 6 1 (white)

2. Reaction with resorcinol in an acidic medium (pharmacopoeia).

Tartrates, when heated with resorcinol meta - C 6 H 4 (OH) 2 in a medium of concentrated sulfuric acid, form cherry red reaction products.

14) Reactions with the ammonia complex of silver. A black precipitate of metallic silver falls out.

15) Reaction with iron (II) sulfate and hydrogen peroxide.

Addition of a dilute aqueous solution of FeSO 4 and H 2 O 2 to a solution containing tartrates. leads to the formation of an unstable iron complex of a crushed color. Subsequent treatment with an alkali solution of NaOH leads to a blue coloration of the complex.

Analytical reactions of the oxalate ion C 2 O 4 2-

Oxalate ion C 2 O 4 2- - anion of dibasic oxalic acid H 2 C 2 O 4 of medium strength, relatively well soluble in water. Oxalate ion in aqueous solutions is colorless, partially hydrolyzed, strong reducing agent, effective ligand - forms stable oxalate complexes with cations of many metals. Oxalates of alkali metals, magnesium and ammonium are soluble in water, while other metals are slightly soluble in water.

1 Reaction with barium chloride Ba 2+ + C 2 O 4 2- \u003d BaC 2 O 4 (white) The precipitate dissolves in mineral acids and in acetic acid (when boiling). 2. Reaction with calcium chloride (pharmacopoeia): Ca 2+ + C 2 O 4 2 - = CaC 2 O 4 (white)

The precipitate is soluble in mineral acids but insoluble in acetic acid.

3. Reaction with silver nitrate.

2 Ag + + C 2 O 4 2 - -> Ag2C2O 4 .|. (curdled) Solubility test. The sediment is divided into 3 parts:

a). Add HNO 3 solution dropwise to the first test tube with the precipitate with stirring until the precipitate dissolves;

b). Add a concentrated solution of ammonia dropwise to the second test tube with a precipitate with stirring until the precipitate dissolves; in). Add 4-5 drops of HCl solution to the third test tube with sediment; a white precipitate of silver chloride remains in the test tube:

Ag 2 C 2 O 4 + 2 HC1 -> 2 AC1 (white) + H 2 C 2 O 4

4. Reaction with potassium permanganate. Oxalate ions with KMPO 4 in an acidic environment are oxidized with the release of CO 2; the KMnO 4 solution becomes colorless due to the reduction of manganese (VII) to manganese (II):

5 C 2 O 4 2 - + 2 MnO 4 "+ 16 H + -> 10 CO 2 + 2 Mp 2+ + 8 H 2 O

Dilute solution of KMPO 4 . The latter is discolored; there is a release of gas bubbles - CO 2 .

38 Elements of the VA group

General characteristics of the VA group of the Periodic Table. in the form s x p y the electronic configuration of the external energy level of the elements of the VA group.

Arsenic and antimony have different allotropic modifications: both with molecular and metallic crystal lattices. However, based on a comparison of the stability of cationic forms (As 3+ , Sb 3+), arsenic is classified as a non-metal, and antimony as a metal.

oxidation states stable for elements of the VA group

From nitrogen to bismuth (with decreasing non-metallic properties):

w decreases the stability of the negative oxidation state (-3) (m. properties of hydrogen compounds)

w the stability of the highest positive oxidation state decreases (+5)

w increases the stability of a low positive oxidation state (+3)

know

• position of carbon and silicon in the periodic table, presence in nature and practical application;
• atomic structure, valency, oxidation states of carbon and silicon;
• methods of obtaining and properties of simple substances - graphite, diamond and silicon; new allotropic forms of carbon;
• main types of carbon and silicon compounds;
• features of the elements of the germanium subgroup;

be able to

• draw up equations for the reactions of obtaining simple substances of carbon and silicon and reactions characterizing the chemical properties of these substances;
• compare the properties of elements in the carbon group;
• characterize practically important compounds of carbon and silicon;
• carry out calculations according to the equations of reactions in which carbon and silicon participate;

own

Skills for predicting the course of reactions involving carbon, silicon and their compounds.

The structure of atoms. Prevalence in nature

Group IVA of the periodic table consists of five elements with even atomic numbers: carbon C, silicon Si, germanium Ge, tin Sn and lead Pb (Table 21.1). In nature, all elements of the group are mixtures of stable isotopes. Carbon has two isogones - *|С (98.9%) and *§С (1.1%). In addition, in nature there are traces of the radioactive isotope "|C with t t= 5730 years. It is constantly formed during collisions of cosmic radiation neutrons with nitrogen nuclei in the earth's atmosphere:

Table 21.1

Characteristics of the elements of the IVA group

* Biogenic element.

The main isotope of carbon is of particular importance in chemistry and physics, since it is based on the atomic mass unit, namely { /2 part of the mass of an atom ‘ICO Yes).

Silicon has three isotopes in nature; among them, the most common is ^)Si (92.23%). Germanium has five isotopes (j^Ge - 36.5%). Tin - 10 isotopes. This is a record among chemical elements. The most common is 12 5 gSn (32.59%). Lead has four isotopes: 2 SgPb (1.4%), 2 S|Pb (24.1%), 2S2βL (22.1%), and 2S2βL (52.4%). The last three isotopes of lead are the end products of the decay of natural radioactive isotopes of uranium and thorium, and therefore their content in the earth's crust has increased throughout the entire existence of the Earth.

In terms of prevalence in the earth's crust, carbon is among the top ten chemical elements. It occurs in the form of graphite, many varieties of coal, as part of oil, natural combustible gas, limestone layers (CaCO e), dolomite (CaCO 3 -MgC0 3) and other carbonates. Although natural diamond makes up an insignificant part of the available carbon, it is extremely valuable as a beautiful and hardest mineral. But, of course, the highest value of carbon lies in the fact that it is the structural basis of bioorganic substances that form the bodies of all living organisms. Carbon is rightly considered the first among many chemical elements necessary for the existence of life.

Silicon is the second most abundant element in the earth's crust. Sand, clay, and many rocks that you see are made up of silicon minerals. With the exception of crystalline varieties of silicon oxide, all of its natural compounds are silicates, i.e. salts of various silicic acids. These acids themselves have not been obtained as individual substances. Orthosilicates contain SiOj ~ ions, metasilicates consist of polymer chains (Si0 3 ") w. Most silicates are built on a framework of silicon and oxygen atoms, between which atoms of any metals and some non-metals (fluorine) can be located. Widely known silicon minerals include quartz Si0 2, feldspars (orthoclase KAlSi 3 0 8), micas (muscovite KAl 3 H 2 Si 3 0 12). In total, more than 400 silicon minerals are known. Silicon compounds are more than half of jewelry and ornamental stones. Oxygen-silicon framework causes low solubility silicon minerals in water.Only from hot underground springs, over thousands of years, growths and crusts of silicon compounds can be deposited.Jasper belongs to rocks of this type.

There is no need to talk about the time of discovery of carbon, silicon, tin and lead, since they have been known in the form of simple substances or compounds since ancient times. Germanium was discovered by K. Winkler (Germany) in 1886 in the rare mineral argyrodite. It soon became clear that the existence of an element with such properties was predicted by D. I. Mendeleev. The naming of the new element caused controversy. Mendeleev, in a letter to Winkler, strongly supported the name germanium.

Group IVA elements have four valence electrons on the outer s- and p-sublevels:

Electronic formulas of atoms:

In the ground state, these elements are divalent, and in the excited state they become tetravalent:

Carbon and silicon form very few chemical compounds in the divalent state; in almost all stable compounds they are tetravalent. Further down the group, for germanium, tin, and lead, the stability of the divalent state increases and the stability of the tetravalent state decreases. Therefore, lead(IV) compounds behave as strong oxidizers. This pattern is also manifested in the VA group. An important difference between carbon and the rest of the elements of the group is the ability to form chemical bonds in three different states of hybridization - sp, sp2 and sp3. Silicon has practically only one hybrid state left. sp3. This is clearly manifested when comparing the properties of carbon and silicon compounds. For example, carbon monoxide CO 2 is a gas (carbon dioxide), and silicon oxide Si0 2 is a refractory substance (quartz). The first substance is gaseous because at sp-hybridization of carbon, all covalent bonds are closed in the CO 2 molecule:

The attraction between molecules is weak, and this determines the state of matter. In silicon oxide, four hybrid 5p 3 silicon orbitals cannot be closed on two oxygen atoms. A silicon atom is bonded to four oxygen atoms, each of which is in turn bonded to another silicon atom. It turns out a frame structure with the same strength of bonds between all atoms (see diagram, vol. 1, p. 40).

Compounds of carbon and silicon with the same hybridization, such as methane CH 4 and silane SiH 4 , are similar in structure and physical properties. Both substances are gases.

The electronegativity of the IVA elements is lower compared to the elements of the VA group, and this is especially noticeable in the elements of the 2nd and 3rd periods. The metallicity of elements in the IVA group is more pronounced than in the VA group. Carbon in the form of graphite is a conductor. Silicon and germanium are semiconductors, while tin and lead are true metals.

Abstract keywords: carbon, silicon, elements of the IVA group, properties of elements, diamond, graphite, carbine, fullerene.

Group IV elements are carbon, silicon, germanium, tin and lead. Let's take a closer look at the properties of carbon and silicon. The table shows the most important characteristics of these elements.

In almost all of their compounds, carbon and silicon tetravalent , their atoms are in an excited state. The configuration of the valence layer of the carbon atom changes when the atom is excited:

The configuration of the valence layer of the silicon atom changes similarly:

The outer energy level of carbon and silicon atoms has 4 unpaired electrons. The radius of the silicon atom is larger; its valence layer has vacant 3 d–orbitals, this causes differences in the nature of the bonds that form silicon atoms.

The oxidation states of carbon vary in the range from –4 to +4.

A characteristic feature of carbon is its ability to form chains: carbon atoms are connected to each other and form stable compounds. Similar silicon compounds are unstable. The ability of carbon to chain formation determines the existence of a huge number organic compounds .

To inorganic compounds carbon include its oxides, carbonic acid, carbonates and bicarbonates, carbides. The remaining carbon compounds are organic.

The element carbon is characterized by allotropy, its allotropic modifications are diamond, graphite, carbine, fullerene. Other allotropic modifications of carbon are now known.

Coal and soot can be considered as amorphous varieties of graphite.

Silicon forms a simple substance - crystalline silicon. There is amorphous silicon - a white powder (without impurities).

The properties of diamond, graphite and crystalline silicon are given in the table.

The reason for the obvious differences in the physical properties of graphite and diamond is due to different the structure of the crystal lattice . In a diamond crystal, each carbon atom (excluding those on the surface of the crystal) forms four equivalent strong bonds with neighboring carbon atoms. These bonds are directed to the vertices of the tetrahedron (as in the CH 4 molecule). Thus, in a diamond crystal, each carbon atom is surrounded by four of the same atoms located at the vertices of a tetrahedron. The symmetry and strength of C–C bonds in a diamond crystal determine the exceptional strength and the absence of electronic conductivity.

AT graphite crystal each carbon atom forms three strong equivalent bonds with neighboring carbon atoms in the same plane at an angle of 120°. In this plane, a layer is formed, consisting of flat six-membered rings.

In addition, each carbon atom has one unpaired electron. These electrons form a common electronic system. The connection between the layers is carried out due to relatively weak intermolecular forces. The layers are arranged one relative to the other in such a way that the carbon atom of one layer is above the center of the hexagon of the other layer. The C–C bond length inside the layer is 0.142 nm, the distance between the layers is 0.335 nm. As a result, bonds between layers are much weaker than bonds between atoms within a layer. This causes graphite properties: It is soft, easy to exfoliate, has a gray color and metallic luster, is electrically conductive and chemically more reactive than diamond. Models of crystal lattices of diamond and graphite are shown in the figure.

Is it possible to turn graphite into diamond? Such a process can be carried out under harsh conditions - at a pressure of approximately 5000 MPa and at temperatures from 1500 ° C to 3000 ° C for several hours in the presence of catalysts (Ni). The bulk of the products are small crystals (from 1 to several mm) and diamond dust.

Carbine- allotropic modification of carbon, in which carbon atoms form linear chains of the type:

–С≡С–С≡С–С≡С–(α-carbine, polyyne) or =C=C=C=C=C=C=(β-carbine, polyene)

The distance between these chains is less than between graphite layers due to stronger intermolecular interaction.

Carbin is a black powder, is a semiconductor. Chemically, it is more active than graphite.

fullerene- allotropic modification of carbon formed by C 60, C 70 or C 84 molecules. On the spherical surface of the C 60 molecule, carbon atoms are located at the vertices of 20 regular hexagons and 12 regular pentagons. All fullerenes are closed structures of carbon atoms. Fullerene crystals are substances with a molecular structure.

Silicon. There is only one stable allotropic modification of silicon, the crystal lattice of which is similar to that of diamond. Silicon - hard, refractory ( t° pl \u003d 1412 ° C), a very fragile substance of dark gray color with a metallic sheen, under standard conditions - a semiconductor.

Elements carbon C, silicon Si, germanium Ge, tin Sn and lead Pb make up the IVA group of the Periodic Table of D.I. Mendeleev. The general electronic formula of the valence level of the atoms of these elements is n s 2n p 2 , the predominant oxidation states of elements in +2 and +4 compounds. By electronegativity, the elements C and Si are classified as non-metals, and Ge, Sn and Pb are classified as amphoteric elements, the metallic properties of which increase with increasing serial number. Therefore, in tin(IV) and lead(IV) compounds, chemical bonds are covalent, for lead(II) and, to a lesser extent, for tin(II), ionic crystals are known. In the series of elements from C to Pb, the stability of the +4 oxidation state decreases, and the +2 oxidation state increases. Lead(IV) compounds are strong oxidizing agents, compounds of other elements in the +2 oxidation state are strong reducing agents.

Simple substances carbon, silicon and germanium are chemically rather inert and do not react with water and non-oxidizing acids. Tin and lead also do not react with water, but under the action of non-oxidizing acids they pass into solution in the form of tin(II) and lead(II) aquacations. Alkalis do not transfer carbon into solution, silicon is transferred with difficulty, and germanium reacts with alkalis only in the presence of oxidizing agents. Tin and lead react with water in an alkaline medium, turning into hydroxo complexes of tin(II) and lead(II). The reactivity of simple substances of the IVA group increases with increasing temperature. So, when heated, they all react with metals and non-metals, as well as with oxidizing acids (HNO 3, H 2 SO 4 (conc.), etc.). In particular, concentrated nitric acid, when heated, oxidizes carbon to CO 2 ; silicon chemically dissolves in a mixture of HNO 3 and HF, turning into hydrogen hexafluorosilicate H 2 . Dilute nitric acid converts tin to tin(II) nitrate, and concentrated nitric acid to hydrated tin(IV) oxide SnO 2 n H 2 O, called β - tin acid. Lead under the action of hot nitric acid forms lead (II) nitrate, while cold nitric acid passivates the surface of this metal (an oxide film is formed).

Carbon in the form of coke is used in metallurgy as a strong reducing agent that forms CO and CO 2 in air. This makes it possible to obtain free Sn and Pb from their oxides - natural SnO 2 and PbO, obtained by roasting ores containing lead sulfide. Silicon can be obtained by the magnesium thermal method from SiO 2 (with an excess of magnesium, Mg 2 Si silicide is also formed).

Chemistry carbon is mainly the chemistry of organic compounds. Of the inorganic derivatives of carbon, carbides are characteristic: salt-like (such as CaC 2 or Al 4 C 3), covalent (SiC) and metal-like (for example, Fe 3 C and WC). Many salt-like carbides are completely hydrolyzed with the release of hydrocarbons (methane, acetylene, etc.).

Carbon forms two oxides: CO and CO 2 . Carbon monoxide is used in pyrometallurgy as a strong reducing agent (it converts metal oxides into metals). CO is also characterized by addition reactions with the formation of carbonyl complexes, for example. Carbon monoxide is a non-salt-forming oxide; it is poisonous ("carbon monoxide"). Carbon dioxide is an acid oxide, in aqueous solution it exists in the form of CO 2 · H 2 O monohydrate and weak dibasic carbonic acid H 2 CO 3. Soluble salts of carbonic acid - carbonates and bicarbonates - due to hydrolysis have pH > 7.

Silicon forms several hydrogen compounds (silanes), which are highly volatile and reactive (self-ignite in air). To obtain silanes, the interaction of silicides (for example, magnesium silicide Mg 2 Si) with water or acids is used.

Silicon in the +4 oxidation state is included in SiO 2 and very numerous and often very complex in structure and composition of silicate ions (SiO 4 4–; Si 2 O 7 6–; Si 3 O 9 6–; Si 4 O 11 6– ; Si 4 O 12 8–, etc.), the elementary fragment of which is a tetrahedral group. Silicon dioxide is an acidic oxide; it reacts with alkalis during fusion (forming polymetasilicates) and in solution (forming orthosilicate ions). From solutions of alkali metal silicates, under the action of acids or carbon dioxide, a precipitate of silicon dioxide hydrate SiO 2 n H 2 O, in equilibrium with which a weak ortho-silicic acid H 4 SiO 4 is always in solution in a small concentration. Aqueous solutions of alkali metal silicates have pH > 7 due to hydrolysis.

Tin and lead in the +2 oxidation state they form the oxides SnO and PbO. Tin(II) oxide is thermally unstable and decomposes into SnO 2 and Sn. Lead(II) oxide, on the other hand, is very stable. It is formed during the combustion of lead in air and is found in nature. Tin(II) and lead(II) hydroxides are amphoteric.

Tin(II) aquacation exhibits strong acidic properties and is therefore stable only at pH< 1 в среде хлорной или азотной кислот, анионы которых не обладают заметной склонностью вхо­дить в состав комплексов олова(II) в качестве лигандов. При раз­бавлении таких растворов выпадают осадки основных солей раз­личного состава. Галогениды олова(II) – ковалентные соединения, поэтому при растворении в воде, например, SnCl 2 протекает внача­ле гидратация с образованием , а затем гидролиз до выпадения осадка вещества условного состава SnCl(OH). При наличии избытка хлороводородной кислоты, SnCl 2 нахо­дится в растворе в виде комплекса – . Большинство солей свинца(II) (например, иодид, хлорид, сульфат, хромат, карбонат, сульфид) малорастворимы в воде.

Tin(IV) and lead(IV) oxides are amphoteric with a predominance of acidic properties. They are answered by EO 2 polyhydrates n H 2 O, passing into solution in the form of hydroxo complexes under the action of an excess of alkalis. Tin(IV) oxide is formed during the combustion of tin in air, and lead(IV) oxide can only be obtained by the action of strong oxidizing agents (for example, calcium hypochlorite) on lead(II) compounds.

Covalent tin(IV) chloride is completely hydrolyzed by water with the release of SnO 2, and lead(IV) chloride decomposes under the action of water, releasing chlorine and being reduced to lead(II) chloride.

Tin(II) compounds exhibit reducing properties, especially strong in an alkaline environment, and lead(IV) compounds exhibit oxidizing properties, especially strong in an acidic environment. A common lead compound is its double oxide (Рb 2 II Рb IV)О 4 . This compound decomposes under the action of nitric acid, and lead (II) passes into solution in the form of a cation, and lead (IV) oxide precipitates. The lead(IV) present in the double oxide is responsible for the strong oxidizing properties of this compound.

Germanium(IV) and tin(IV) sulfides, due to the amphoteric nature of these elements, when an excess of sodium sulfide is added, form soluble thiosalts, for example, Na 2 GeS 3 or Na 2 SnS 3 . The same tin(IV) thiosalt can be obtained from tin(II) sulfide SnS by its oxidation with sodium polysulfide. Thiosalts are destroyed under the action of strong acids with the release of gaseous H 2 S and a deposit of GeS 2 or SnS 2 . Lead(II) sulfide does not react with polysulfides, and lead(IV) sulfide is unknown.