What is manganese: we study a chemical element. Oxidation state

Chemistry of metals

Lecture 2. The main issues discussed in the lecture

Metals of VIIB-subgroup

General characteristics of metals of the VIIB-subgroup.

Manganese chemistry

Natural compounds Mn

Physical and Chemical properties metal.

Mn compounds. Redox properties of compounds

Brief characteristics of Tc and Re.

Metals of VIIB-subgroup

general characteristics

appear in natural compounds. The most common

strange Mn minerals: pyrolusite MnO2 and rhodochrosite MnCO3.

Mn (+7) and (+6) compounds are strong oxidizing agents.

Mn, Tc, Re are most similar in the highest degree oxide

lehenia, it is expressed in the acidic nature of higher oxides and hydroxides.

The higher hydroxides of all elements of the VIIB-subgroup are strong

acids with the general formula NEO4.

In the highest oxidation state, the elements Mn, Tc, Re are similar to the element of the main subgroup chlorine. Acids: HMnO4, HTcO4, HReO4 and

HClO4 are strong. Elements of the VIIB-subgroup are characterized by a noticeable

It is very similar to its neighbors in the row, in particular, Mn is similar to Fe. In nature, Mn compounds always coexist with Fe compounds.

M ar ganets

Typical oxidation states

neutral, slightly alkaline and slightly acidic environment.

Mn (+7) and (+6) compounds exhibit strong oxidizing properties.

The acid-base character of Mn oxides and hydroxides is naturally due to

varies depending on the oxidation state: in the oxidation state +2 oxide and hydroxide are basic, and in the highest oxidation state they are acidic,

moreover, HMnO4 is a strong acid.

In aqueous solutions, Mn (+2) exists in the form of aquacations

2+, which for simplicity denotes Mn2 +. Manganese in high oxidation states is in solution in the form of tetraoxoanions: MnO4 2– and

MnO4 -.

Natural compounds and metal production

The element Mn is most abundant in the earth's crust among heavy metal

Fishing follows iron, but is noticeably inferior to it - the Fe content is about 5%, and Mn is only about 0.1%. Manganese has more common oxide

ny and carbonate and ores. The most important minerals are: pyrol-

zite MnO2 and rhodochrosite MnCO3.

to obtain Mn

In addition to these minerals, hausmanite Mn3 O4 is used to obtain Mn.

and hydrated psilomelan oxide MnO2. xH2 O. In manganese ores, all

Manganese is mainly used in the production of special steels with high strength and impact resistance. Therefore, os-

a new amount of Mn is obtained not in pure form, but in the form of ferromanganese

tsa - an alloy of manganese and iron, containing from 70 to 88% Mn.

The total volume of the annual world production of manganese, including in the form of ferromanganese, ~ (10 12) million tons / year.

To obtain ferromanganese, manganese oxide ore was reduced

coal.

MnO2 + 2C = Mn + 2CO

Together with the Mn oxides, the Fe oxides contained in the ru-

de. To obtain manganese with a minimum content of Fe and C, compounds

Fe is preliminarily separated and mixed oxide Mn3 O4 is obtained

(MnO. Mn2 O3). It is then reduced with aluminum (pyrolusite reacts with

Al is too violent).

3Mn3 O4 + 8Al = 9Mn + 4Al2 O3

Pure manganese is obtained by hydrometallurgical method. After preliminary preparation of the MnSO4 salt, through a solution of Mn sulfate,

let electricity, manganese is reduced at the cathode:

Mn2 + + 2e– = Mn0.

Simple substance

Manganese is a light gray metal. Density - 7.4 g / cm3. Melting point - 1245 ° C.

Mn2 +. When heated, powdered manganese interacts with water with

release of H2.

Due to oxidation in air, manganese becomes covered with brown spots,

When heated, manganese reacts with halogens and sulfur. Affinity Mn

to sulfur more than iron, therefore, when adding ferromanganese to steel,

the sulfur dissolved in it binds to MnS. MnS sulfide does not dissolve in the metal and goes into the slag. The strength of the steel increases after the removal of the brittle sulfur.

With very high temperatures(> 1200 0 С) manganese, interacting with nitrogen and carbon, forms non-stoichiometric nitrides and carbides.

Manganese compounds

Manganese compounds (+7)

All Mn (+7) compounds exhibit strong oxidizing properties.

Potassium permanganate KMnO 4 - the most common compound

Mn (+7). In its pure form, it is crystalline substance dark-

purple. When heating crystalline permanganate, it decomposes

To slow down this reaction, which is accelerated by light, KMnO4 solutions are stored

nat in dark bottles.

When a few drops are added to the permanganate crystals,

Trated sulfuric acid forms manganic anhydride.

2KMnO4 + H2 SO4 2Mn2 O7 + K2 SO4 + H2 O

Mn 2 O 7 oxide is a dark green heavy oily liquid. This is the only metal oxide that, when normal conditions find

in liquid state(melting point 5.9 0 С). The oxide has a molecular

a curious structure, very unstable, at 55 0 С it decomposes with an explosion. 2Mn2 O7 = 4MnO2 + 3O2

Mn2 O7 oxide is a very strong and energetic oxidizing agent. Many or-

ganic substances are oxidized under its influence to CO2 and H2O. Oxide

Mn2 O7 is sometimes called chemical matches. If a glass rod is moistened with Mn2 O7 and brought to an alcohol lamp, it will light up.

When Mn2 O7 dissolves in water, manganic acid is formed.

Acid HMnO 4 is a strong acid that exists only in water

nominal solution, in a free state it is not isolated. The acid HMnO4 decomposes

with the release of O2 and MnO2.

When solid alkali is added to the KMnO4 solution,

green manganate.

4KMnO4 + 4KOH (c) = 4K2 MnO4 + O2 + 2H2 O.

When heated, KMnO4 with concentrated hydrochloric acid forms

Cl2 gas is supplied.

2KMnO4 (q) + 16HCl (conc.) = 2MnCl2 + 5Cl2 + 8H2 O + 2KCl

In these reactions, the strong oxidizing properties of permanganate are manifested.

The products of the interaction of KMnO4 with reducing agents depend on the acidity of the solution. in which the reaction takes place.

In acidic solutions, a colorless cation Mn2 + is formed.

MnO4 - + 8H + + 5e–  Mn2 + + 4H2 O; (E0 = +1.53 V).

A brown precipitate of MnO2 precipitates from neutral solutions.

MnO4 - + 2H2 O + 3e–  MnO2 + 4OH–.

In alkaline solutions, the green anion MnO4 2– is formed.

Potassium permanganate is industrially obtained either from manganese

(oxidizing it at the anode in an alkaline solution), or from pyrolusite (MnO2 pre-

they are oxidized by variationally to K2 MnO4, which is then oxidized at the anode to KMnO4).

Manganese compounds (+6)

Manganates - salts with the anion MnO4 2–, have a bright green color.

Anion MnO4 2─ is stable only in strongly alkaline environment... Under the action of water and, especially, acid, manganates disproportionate with the formation of compounds

Mn in oxidation states 4 and 7.

3MnO4 2– + 2H2 O = MnO2 + 2MnO4 - + 4OH–

For this reason, the acid H2 MnO4 does not exist.

Manganates can be obtained by fusing MnO2 with alkalis or carbonate-

mi in the presence of an oxidizing agent.

2MnO2 (q) + 4KOH (l) + О2 = 2K2 MnO4 + 2H2 O

Manganates are strong oxidizing agents , but if they are affected

with an even stronger oxidizing agent, then they pass into permanganates.

Disproportionation

Manganese compounds (+4)

- the most stable Mn compound. This oxide occurs naturally (pyrolusite mineral).

MnO2 oxide is a black-brown substance with a very strong crystalline

lattice (the same as that of rutile TiO2). For this reason, despite the fact that MnO 2 is amphoteric, it does not react with alkali solutions and with dilute acids (as well as TiO2). It dissolves in concentrated acids.

MnO2 + 4HCl (conc.) = MnCl2 + Cl2 + 2H2 O

The reaction is used in the laboratory to produce Cl2.

When MnO2 is dissolved in concentrated sulfuric and nitric acid Mn2 + and O2 are formed.

Thus, in a very acidic environment, MnO2 tends to go into

Mn2 + cation.

MnO2 reacts with alkalis only in melts with the formation of mixed

ny oxides. In the presence of an oxidizing agent, manganates are formed in alkaline melts.

MnO2 oxide is used industrially as a cheap oxidizing agent. In particular, redox interaction

by the formation of oxides Mn2 O3 and Mn3 O4 (MnO. Mn2 O3).

Hydroxide Mn (+4) is not isolated, during the reduction of permanganate and man-

ganata in neutral or slightly alkaline media, as well as during oxidation

Mn (OH) 2 and MnOOH, a dark brown precipitate is precipitated from solutions.

MnO2.

Mn oxide and hydroxide (+3) are basic in nature. It's solid

brown, water-insoluble and unstable substances.

When interacting with dilute acids, they are disproportionate

they form Mn compounds in oxidation states 4 and 2.2MnOOH + H2 SO4 = MnSO4 + MnO2 + 2H2 O

They interact with concentrated acids in the same way as

MnO2, i.e. in an acidic medium they pass into the Mn2 + cation. In an alkaline environment, they are easily oxidized in air to MnO2.

Manganese compounds (+2)

In aqueous solutions, Mn (+2) compounds are stable in an acidic environment.

Oxide and hydroxide Mn (+2) have a basic character, easily dissolve

ripple in acids with the formation of a hydrated Mn2 + cation.

MnO oxide - gray-green refractory crystalline compound

(melting point - 18420 C). It can be obtained by decomposing car-

bonata in the absence of oxygen.

MnCO3 = MnO + CO2.

MnO does not dissolve in water.

PART 1

1. The oxidation state (s. O.) Is the conditional charge of the atoms of a chemical element in a complex substance, calculated on the basis of the assumption that it consists of simple ions.

You should know!

1) In connections with. O. hydrogen = +1, except for hydrides .
2) In connections with. O. oxygen = -2, except for peroxides  and fluorides 
3) The oxidation state of metals is always positive.

For metals of the main subgroups of the first three groups, p. O. constant:

Group IA metals - p. O. = +1,
Group IIA metals - p. O. = +2,
Group IIIA metals - p. O. = +3. 4

Free atoms and simple substances with. O. = 0.5

Total s. O. all elements in the compound = 0.

2. The way names are formed two-element (binary) compounds.

4. Complete the table "Names and formulas of binary compounds".

5. Determine the oxidation state of the highlighted element of the complex compound.

PART 2

1. Determine the oxidation state of chemical elements in compounds by their formulas. Write down the names of these substances.

2. Divide the substances FeO, Fe2O3, CaCl2, AlBr3, CuO, K2O, BaCl2, SO3 into two groups. Write down the names of the substances, indicating the degree of oxidation.

3. Establish a correspondence between the name and the oxidation state of the atom of a chemical element and the formula of the compound.

4. Make formulas of substances by name.

5. How many molecules are contained in 48 g of sulfur (IV) oxide?

6.Using the Internet and other sources of information, prepare a message on the use of any binary connection according to the following plan:

1) formula;
2) name;
3) properties;
4) application.

H2O water, hydrogen oxide. Water under normal conditions is liquid, colorless, odorless, in a thick layer - blue. The boiling point is about 100⁰С. It is a good solvent. A water molecule consists of two hydrogen atoms and one oxygen atom; this is its qualitative and quantitative composition. This is a complex substance, it is characterized by the following chemical properties: interaction with alkali metals, alkaline earth metals.

The exchange reactions with water are called hydrolysis. These reactions are of great importance in chemistry.

7. The oxidation state of manganese in the K2MnO4 compound is:

8. The lowest oxidation state of chromium is in the compound, the formula of which is:

1) Cr2O3

9. Chlorine exhibits the maximum oxidation state in a compound, the formula of which is:

Olympiad tasks in chemistry

(1 school stage)

1. Test

1.Manganese has the highest oxidation state in the compound

2. The neutralization reaction corresponds to the abbreviated ionic equation

1) H + + OH - = H 2 O

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

3) CaO + 2H + = Ca 2+ + H 2 O

4) Zn + 2H + = Zn 2+ + H 2

3. Interact with each other

2) MnO and Na 2 O

3) P 2 O 5 and SO 3

4. The equation of the redox reaction is

1) KOH + HNO 3 = KNO 3 + H 2 O

2) N 2 O 5 + H 2 O = 2 HNO 3

3) 2N 2 O = 2N 2 + O 2

4) BaCO 3 = BaO + CO 2

5. The exchange reaction is interaction

1) calcium oxide with nitric acid

2) carbon monoxide with oxygen

3) ethylene with oxygen

4) hydrochloric acid with magnesium

6. Acid rain caused by the presence in the atmosphere

1) nitrogen and sulfur oxides

4) natural gas

7. Methane, along with gasoline and diesel fuel, is used as fuel in internal combustion engines (motor vehicles). The thermochemical equation of combustion of gaseous methane has the form:

CH 4 + 2O 2 = CO 2 + 2H 2 O + 880 kJ

What amount of kJ of heat will be released during the combustion of CH 4 with a volume of 112 liters (at standard level)?

Choose the correct answer:

2. Tasks

1. In the equation of the redox reaction, place the coefficients in any way you know.

SnSO 4 + KMnO 4 + H 2 SO 4 = Sn (SO 4) 2 + MnSO 4 + K 2 SO 4 + H 2 O

Indicate the names of the oxidizing agent and reducing agent and the oxidation state of the elements. (4 points)

2. Write down the reaction equations allowing to carry out the following transformations:

(2) (3) (4) (5)

CO 2 → Ca (HCO 3) 2 → CaCO 3 → CaO → CaCl 2 → CaCO 3

(5 points)

3. Determine the alkadiene formula if its relative density by air is 1.862 (3 points)

4. In 1928, the American chemist of the corporation General Motors (General Motors Research) Thomas Midgley Jr. succeeded in synthesizing and isolating in his laboratory a chemical compound consisting of 23.53% carbon, 1.96% hydrogen and 74.51 % fluorine. The resulting gas was 3.52 times heavier than air and did not burn. Derive the formula of the compound, write down the structural formulas of organic substances corresponding to the obtained molecular formula, give them names. (6 points).

5. Mixed 140 g of 0.5% hydrochloric acid solution with 200 g of 3% hydrochloric acid solution. What is the percentage of hydrochloric acid in the newly obtained solution? (3 points)

3. Crossword

Unravel the words encrypted in the crossword puzzle

Legend: 1 → - horizontally

1 ↓ - vertical

↓ Corrosion product of iron.

→ Formed by the interaction of (6) with the basic oxide.

→ Unit of the amount of heat.

→ Positively charged ion.

→ An Italian scientist, after whom one of the most important constants is named.

→ The number of electrons per external level element number 14.

→ …… gas - carbon monoxide (IV).

→ The great Russian scientist is famous, including as the creator of mosaic paintings, the author of the epigraph.

→ Type of reaction between sodium hydroxide and sulfuric acid solutions.

Give an example of a reaction equation for (1 →).

Indicate the constant mentioned in (4).

Write down the reaction equation (8).

Write electronic structure atom element, which is mentioned in (5). (13 points)

The electronic configuration of the unexcited manganese atom is 3d 5 4s 2; the excited state is expressed by the electronic formula 3d 5 4s 1 4p 1.

The oxidation states +2, +4, +6, +7 are most typical for manganese in compounds.

Manganese is a silvery-white, brittle, quite active metal: in the series of voltages, it is located between aluminum and zinc. Manganese is covered in air oxide film protecting it from further oxidation. In a finely divided state, manganese is easily oxidized.

Manganese (II) oxide MnO and the corresponding hydroxide Mn (OH) 2 have basic properties - when they interact with acids, divalent manganese salts are formed: Mn (OH) 2 + 2 H + ® Mn 2+ + 2 H 2 O.

Mn 2+ cations are also formed upon dissolution of metallic manganese in acids. Manganese (II) compounds exhibit reducing properties, for example, the white precipitate Mn (OH) 2 darkens rapidly in air, gradually oxidizing to MnO 2: 2 Mn (OH) 2 + O 2 ® 2 MnO 2 + 2 H 2 O.

Manganese (IV) oxide MnO 2 is the most stable manganese compound; it is easily formed both during the oxidation of manganese compounds in a lower oxidation state (+2), and during the reduction of manganese compounds in higher oxidation states (+6, +7):

Mn (OH) 2 + H 2 O 2 ® MnO 2 + 2 H 2 O;

2 KMnO 4 + 3 Na 2 SO 3 + H 2 O ® 2 MnO 2 ¯ + 3 Na 2 SO 4 + 2 KOH.

MnO 2 is an amphoteric oxide, however, it is acidic, and its basic properties are poorly expressed. One of the reasons that MnO 2 does not show clearly expressed basic properties is its strong oxidative activity in an acidic medium (= +1.23 V): MnO 2 is reduced to Mn 2+ ions, and does not form stable salts of tetravalent manganese. The hydrated form corresponding to manganese (IV) oxide should be considered as hydrated manganese dioxide MnO 2 × xH 2 O. Manganese (IV) oxide as an amphoteric oxide formally corresponds to ortho- and meta-forms of permanganous acid not isolated in the free state: H 4 MnO 4 - ortho-form and H 2 MnO 3 - meta-form. Known manganese oxide Mn 3 O 4, which can be considered as a salt of divalent manganese of the ortho-form of permanganous acid Mn 2 MnO 4 - manganese (II) orthomanganite. There are reports in the literature on the existence of oxide Mn 2 O 3. The existence of this oxide can be explained by considering it as a salt of divalent manganese of the meta-form of permanganate acid: MnMnO 3 - manganese (II) metamanganite.

When manganese dioxide is fused with oxidants such as chlorate or potassium nitrate in an alkaline medium, tetravalent manganese is oxidized to a hexavalent state, and potassium manganate is formed, a salt that is very unstable even in a solution of permanganous acid H 2 MnO 4, the anhydride of which (MnO 3) is unknown:

MnO 2 + KNO 3 + 2 KOH ® K 2 MnO 4 + KNO 2 + H 2 O.

Manganates are unstable and prone to disproportionate reversible reaction: 3 K 2 MnO 4 + 2 H 2 O ⇆ 2 KMnO 4 + MnO 2 ¯ + 4 KOH,

as a result, the green color of the solution, caused by the manganate ions MnO 4 2–, changes to a violet color, which is characteristic of the permanganate ions MnO 4 -.

The most widely used compound of heptavalent manganese is potassium permanganate KMnO 4 - a salt known only in a solution of manganic acid HMnO 4. Potassium permanganate can be obtained by oxidizing manganates with strong oxidants, for example, chlorine:

2 K 2 MnO 4 + Cl 2 ® 2 KMnO 4 + 2 KCl.

Manganese oxide (VII), or manganese anhydride, Mn 2 O 7 is an explosive green-brown liquid. Mn 2 O 7 can be obtained by the reaction:

2 KMnO 4 + 2 H 2 SO 4 (conc.) ® Mn 2 O 7 + 2 KHSO 4 + H 2 O.

Manganese compounds in the highest oxidation state +7, in particular permanganates, are strong oxidizing agents. The depth of reduction of permanganate ions and their oxidative activity depends on the pH of the medium.

In a strongly acidic environment, the product of the reduction of permanganates is the Mn 2+ ion, and bivalent manganese salts are obtained:

MnO 4 - + 8 H + + 5 e - ® Mn 2+ + 4 H 2 O (= +1.51 V).

In a neutral, slightly alkaline or slightly acidic medium, as a result of the reduction of permanganate ions, MnO 2 is formed:

MnO 4 - + 2 H 2 O + 3 e - ® MnO 2 ¯ + 4 OH - (= +0.60 V).

MnO 4 - + 4 H + + 3 e - ® MnO 2 ¯ + 2 H 2 O (= +1.69 V).

In a strongly alkaline medium, permanganate ions are reduced to manganate ions MnO 4 2–, and salts of the type K 2 MnO 4, Na 2 MnO 4 are formed:

MnO 4 - + e - ® MnO 4 2– (= +0.56 V).