Basic chemical properties of iron. Iron

17. d - elements. Iron, general characteristics, properties. Oxides and hydroxides, CO and OM characteristics, biorole, ability to complex formation.

1. General characteristics.

Iron - d-element of the secondary subgroup of the eighth group of the fourth period of PSCE with atomic number 26.

One of the most common metals in the earth's crust (second place after aluminum).

A simple substance iron is a malleable silver-white metal with a high chemical reactivity: iron quickly corrodes at high temperatures or high humidity in the air.

4Fe + 3O2 + 6H2O = 4Fe(OH)3

In pure oxygen, iron burns, and in a finely dispersed state, it ignites spontaneously in air.

3Fe + 2O2 = FeO + Fe2O3

3Fe + 4H2O = FeO*Fe2O3

FeO*Fe2O3 = Fe3O4 (iron scale)

Actually, iron is usually called its alloys with a low content of impurities (up to 0.8%), which retain the softness and ductility of pure metal. But in practice, alloys of iron with carbon are more often used: steel (up to 2.14 wt.% carbon) and cast iron (more than 2.14 wt.% carbon), as well as stainless (alloyed) steel with the addition of alloying metals (chromium, manganese, nickel, etc.). The combination of the specific properties of iron and its alloys make it "metal No. 1" in importance to humans.

In nature, iron is rarely found in its pure form, most often it occurs as part of iron-nickel meteorites. The prevalence of iron in the earth's crust is 4.65% (4th place after O, Si, Al). It is also believed that iron makes up most of the earth's core.

2.Properties

1.Physical St. Iron is a typical metal, in the free state it is silvery-white in color with a grayish tinge. Pure metal is ductile, various impurities (in particular, carbon) increase its hardness and brittleness. It has pronounced magnetic properties. The so-called "iron triad" is often distinguished - a group of three metals (iron Fe, cobalt Co, nickel Ni) that have similar physical properties, atomic radii and electronegativity values.

2.Chemical St. Islands.

Oxidation state	Oxide	Hydroxide	Character	Notes
			Weakly basic
			Very weak base, sometimes amphoteric
	Not received	*	Acid	Strong oxidizing agent

For iron, the oxidation states of iron are characteristic - +2 and +3.

The oxidation state +2 corresponds to black oxide FeO and green hydroxide Fe(OH) 2 . They are basic. In salts, Fe(+2) is present as a cation. Fe(+2) is a weak reducing agent.

+3 oxidation states correspond to red-brown Fe 2 O 3 oxide and brown Fe(OH) 3 hydroxide. They are amphoteric in nature, although their acidic and basic properties are weakly expressed. So, Fe 3+ ions are completely hydrolyzed even in an acidic environment. Fe (OH) 3 dissolves (and even then not completely), only in concentrated alkalis. Fe 2 O 3 reacts with alkalis only when fused, giving ferrites(formal salts of an acid that does not exist in the free form of acid HFeO 2):

Iron (+3) most often exhibits weak oxidizing properties.

The +2 and +3 oxidation states easily transition between themselves when the redox conditions change.

In addition, there is Fe 3 O 4 oxide, the formal oxidation state of iron in which is +8/3. However, this oxide can also be considered as iron (II) ferrite Fe +2 (Fe +3 O 2) 2 .

There is also an oxidation state of +6. The corresponding oxide and hydroxide do not exist in free form, but salts - ferrates (for example, K 2 FeO 4) have been obtained. Iron (+6) is in them in the form of an anion. Ferrates are strong oxidizing agents.

Pure metallic iron is stable in water and in dilute solutions. alkalis. Iron does not dissolve in cold concentrated sulfuric and nitric acids due to the passivation of the metal surface with a strong oxide film. Hot concentrated sulfuric acid, being a stronger oxidizing agent, interacts with iron.

WITH hydrochloric and diluted (about 20%) sulfuric acids iron reacts to form iron(II) salts:

When iron reacts with approximately 70% sulfuric acid when heated, the reaction proceeds with the formation iron(III) sulfate:

3. Oxides and hydroxides, CO and OM char-ka ...

Iron(II) compounds

Iron oxide (II) FeO has basic properties, it corresponds to the base Fe (OH) 2. Salts of iron (II) have a light green color. When stored, especially in moist air, they turn brown due to oxidation to iron (III). The same process occurs during storage of aqueous solutions of iron(II) salts:

Of iron(II) salts in aqueous solutions, stable mora salt- double ammonium and iron (II) sulfate (NH 4) 2 Fe (SO 4) 2 6H 2 O.

The reagent for Fe 2+ ions in solution can be potassium hexacyanoferrate(III) K 3 (red blood salt). When Fe 2+ and 3− ions interact, a precipitate turnbull blue:

For the quantitative determination of iron (II) in solution, use phenanthroline, which forms a red FePhen 3 complex with iron (II) in a wide pH range (4-9)

Iron(III) compounds

Iron(III) oxide Fe 2 O 3 weakly amphoterene, it corresponds to an even weaker than Fe (OH) 2, base Fe (OH) 3, which reacts with acids:

Fe 3+ salts tend to form crystalline hydrates. In them, the Fe 3+ ion is usually surrounded by six water molecules. Such salts are pink or purple in color. The Fe 3+ ion is completely hydrolyzed even in an acidic environment. At pH>4, this ion is almost completely precipitated in the form of Fe (OH) 3:

With partial hydrolysis of the Fe 3+ ion, polynuclear oxo- and hydroxocations are formed, due to which the solutions become brown. The main properties of iron (III) hydroxide Fe (OH) 3 are very weakly expressed. It is able to react only with concentrated alkali solutions:

The resulting iron(III) hydroxocomplexes are stable only in strongly alkaline solutions. When solutions are diluted with water, they are destroyed, and Fe (OH) 3 precipitates.

When fused with alkalis and oxides of other metals, Fe 2 O 3 forms a variety of ferrites:

Iron(III) compounds in solutions are reduced by metallic iron:

Iron(III) is capable of forming double sulfates with singly charged cations type alum, for example, KFe (SO 4) 2 - potassium iron alum, (NH 4) Fe (SO 4) 2 - iron ammonium alum, etc.

For qualitative detection of iron(III) compounds in a solution, a qualitative reaction of Fe 3+ ions with thiocyanate ions is used SCN − . When Fe 3+ ions interact with SCN − anions, a mixture of bright red iron thiocyanate complexes 2+ , + , Fe(SCN) 3 , - is formed. The composition of the mixture (and hence the intensity of its color) depends on various factors, so this method is not applicable for the accurate qualitative determination of iron.

Another high-quality reagent for Fe 3+ ions is potassium hexacyanoferrate(II) K 4 (yellow blood salt). When Fe 3+ and 4− ions interact, a bright blue precipitate is formed prussian blue:

Iron(VI) compounds

ferrates- salts of iron acid H 2 FeO 4 that do not exist in free form. These are violet-colored compounds, reminiscent of permanganates in oxidizing properties, and sulfates in solubility. Ferrates are obtained by the action of gaseous chlorine or ozone on a suspension of Fe (OH) 3 in alkali , for example, potassium ferrate(VI) K 2 FeO 4 . Ferrates are colored purple.

Ferrates can also be obtained electrolysis 30% alkali solution on an iron anode:

Ferrates are strong oxidizing agents. In an acidic environment, they decompose with the release of oxygen:

The oxidizing properties of ferrates are used to water disinfection.

4.Biorol

1) In living organisms, iron is an important trace element that catalyzes the processes of oxygen exchange (respiration).

2) Iron is usually included in enzymes in the form of a complex. In particular, this complex is present in hemoglobin, the most important protein that provides oxygen transport with blood to all organs of humans and animals. And it is he who stains the blood in a characteristic red color.

4) An excessive dose of iron (200 mg and above) can have a toxic effect. An overdose of iron depresses the antioxidant system of the body, so it is not recommended to use iron preparations for healthy people.

DEFINITION

Iron- an element of the eighth group of the fourth period of the Periodic system of chemical elements of D. I. Mendeleev.

And the languid number is 26. The symbol is Fe (lat. “ferrum”). One of the most common metals in the earth's crust (second place after aluminum).

Physical properties of iron

Iron is a gray metal. In its pure form, it is quite soft, malleable and ductile. The electronic configuration of the external energy level is 3d 6 4s 2 . In its compounds, iron exhibits the oxidation states "+2" and "+3". The melting point of iron is 1539C. Iron forms two crystalline modifications: α- and γ-iron. The first of them has a cubic body-centered lattice, the second has a cubic face-centered one. α-Iron is thermodynamically stable in two temperature ranges: below 912 and from 1394C to the melting point. Between 912 and 1394C, γ-iron is stable.

The mechanical properties of iron depend on its purity - the content in it of even very small amounts of other elements. Solid iron has the ability to dissolve many elements in itself.

Chemical properties of iron

In moist air, iron quickly rusts, i.e. covered with a brown coating of hydrated iron oxide, which, due to its friability, does not protect iron from further oxidation. In water, iron corrodes intensively; with abundant access of oxygen, hydrated forms of iron oxide (III) are formed:

2Fe + 3/2O 2 + nH 2 O = Fe 2 O 3 × H 2 O.

With a lack of oxygen or with difficult access, a mixed oxide (II, III) Fe 3 O 4 is formed:

3Fe + 4H 2 O (v) ↔ Fe 3 O 4 + 4H 2.

Iron dissolves in hydrochloric acid of any concentration:

Fe + 2HCl \u003d FeCl 2 + H 2.

Similarly, dissolution occurs in dilute sulfuric acid:

Fe + H 2 SO 4 \u003d FeSO 4 + H 2.

In concentrated solutions of sulfuric acid, iron is oxidized to iron (III):

2Fe + 6H 2 SO 4 \u003d Fe 2 (SO 4) 3 + 3SO 2 + 6H 2 O.

However, in sulfuric acid, the concentration of which is close to 100%, iron becomes passive and there is practically no interaction. In dilute and moderately concentrated solutions of nitric acid, iron dissolves:

Fe + 4HNO 3 \u003d Fe (NO 3) 3 + NO + 2H 2 O.

At high concentrations of nitric acid, dissolution slows down and iron becomes passive.

Like other metals, iron reacts with simple substances. The reactions of the interaction of iron with halogens (regardless of the type of halogen) proceed when heated. The interaction of iron with bromine proceeds at an increased vapor pressure of the latter:

2Fe + 3Cl 2 \u003d 2FeCl 3;

3Fe + 4I 2 = Fe 3 I 8.

The interaction of iron with sulfur (powder), nitrogen and phosphorus also occurs when heated:

6Fe + N 2 = 2Fe 3 N;

2Fe + P = Fe 2 P;

3Fe + P = Fe 3 P.

Iron is able to react with non-metals such as carbon and silicon:

3Fe + C = Fe 3 C;

Among the reactions of the interaction of iron with complex substances, the following reactions play a special role - iron is able to reduce metals that are in the activity series to the right of it, from salt solutions (1), to reduce iron (III) compounds (2):

Fe + CuSO 4 \u003d FeSO 4 + Cu (1);

Fe + 2FeCl 3 = 3FeCl 2 (2).

Iron, at elevated pressure, reacts with a non-salt-forming oxide - CO to form substances of complex composition - carbonyls - Fe (CO) 5, Fe 2 (CO) 9 and Fe 3 (CO) 12.

Iron, in the absence of impurities, is stable in water and in dilute alkali solutions.

Getting iron

The main way to obtain iron is from iron ore (hematite, magnetite) or electrolysis of solutions of its salts (in this case, “pure” iron is obtained, i.e. iron without impurities).

Examples of problem solving

EXAMPLE 1

Exercise

Iron scale Fe 3 O 4 weighing 10 g was first treated with 150 ml of hydrochloric acid solution (density 1.1 g/ml) with a mass fraction of hydrogen chloride 20%, and then an excess of iron was added to the resulting solution. Determine the composition of the solution (in % by weight).

Solution

We write the reaction equations according to the condition of the problem: 8HCl + Fe 3 O 4 \u003d FeCl 2 + 2FeCl 3 + 4H 2 O (1); 2FeCl 3 + Fe = 3FeCl 2 (2). Knowing the density and volume of a hydrochloric acid solution, you can find its mass: m sol (HCl) = V(HCl) × ρ (HCl); m sol (HCl) \u003d 150 × 1.1 \u003d 165 g. Calculate the mass of hydrogen chloride: m(HCl)=msol(HCl)×ω(HCl)/100%; m(HCl) = 165 x 20%/100% = 33 g. The molar mass (mass of one mol) of hydrochloric acid, calculated using the table of chemical elements of D.I. Mendeleev - 36.5 g / mol. Find the amount of hydrogen chloride substance: v(HCl) = m(HCl)/M(HCl); v (HCl) \u003d 33 / 36.5 \u003d 0.904 mol. Molar mass (mass of one mole) of scale, calculated using the table of chemical elements of D.I. Mendeleev - 232 g/mol. Find the amount of scale substance: v (Fe 3 O 4) \u003d 10/232 \u003d 0.043 mol. According to equation 1, v(HCl): v(Fe 3 O 4) \u003d 1: 8, therefore, v (HCl) \u003d 8 v (Fe 3 O 4) \u003d 0.344 mol. Then, the amount of hydrogen chloride substance calculated according to the equation (0.344 mol) will be less than that indicated in the condition of the problem (0.904 mol). Therefore, hydrochloric acid is in excess and another reaction will proceed: Fe + 2HCl = FeCl 2 + H 2 (3). Let's determine the amount of iron chloride substance formed as a result of the first reaction (indices denote a specific reaction): v 1 (FeCl 2): ​​v (Fe 2 O 3) = 1:1 = 0.043 mol; v 1 (FeCl 3): v (Fe 2 O 3) = 2:1; v 1 (FeCl 3) = 2 × v (Fe 2 O 3) = 0.086 mol. Let's determine the amount of hydrogen chloride that did not react in reaction 1 and the amount of iron (II) chloride substance formed during reaction 3: v rem (HCl) \u003d v (HCl) - v 1 (HCl) \u003d 0.904 - 0.344 \u003d 0.56 mol; v 3 (FeCl 2): ​​v rem (HCl) = 1:2; v 3 (FeCl 2) \u003d 1/2 × v rem (HCl) \u003d 0.28 mol. Let's determine the amount of FeCl 2 substance formed during reaction 2, the total amount of FeCl 2 substance and its mass: v 2 (FeCl 3) = v 1 (FeCl 3) = 0.086 mol; v 2 (FeCl 2): ​​v 2 (FeCl 3) = 3:2; v 2 (FeCl 2) = 3/2× v 2 (FeCl 3) = 0.129 mol; v sum (FeCl 2) \u003d v 1 (FeCl 2) + v 2 (FeCl 2) + v 3 (FeCl 2) \u003d 0.043 + 0.129 + 0.28 \u003d 0.452 mol; m (FeCl 2) \u003d v sum (FeCl 2) × M (FeCl 2) \u003d 0.452 × 127 \u003d 57.404 g. Let us determine the amount of substance and the mass of iron that entered into reactions 2 and 3: v 2 (Fe): v 2 (FeCl 3) = 1:2; v 2 (Fe) \u003d 1/2 × v 2 (FeCl 3) \u003d 0.043 mol; v 3 (Fe): v rem (HCl) = 1:2; v 3 (Fe) = 1/2×v rem (HCl) = 0.28 mol; v sum (Fe) \u003d v 2 (Fe) + v 3 (Fe) \u003d 0.043 + 0.28 \u003d 0.323 mol; m(Fe) = v sum (Fe) ×M(Fe) = 0.323 ×56 = 18.088 g. Let us calculate the amount of substance and the mass of hydrogen released in reaction 3: v (H 2) \u003d 1/2 × v rem (HCl) \u003d 0.28 mol; m (H 2) \u003d v (H 2) × M (H 2) \u003d 0.28 × 2 \u003d 0.56 g. We determine the mass of the resulting solution m ' sol and the mass fraction of FeCl 2 in it: m’ sol \u003d m sol (HCl) + m (Fe 3 O 4) + m (Fe) - m (H 2);

Lesson Objectives:

• To introduce students to the element of the side group of the Periodic system - iron, its structure, properties.
• To know the presence of iron in nature, methods of its production, application, physical properties.
• Be able to characterize iron as an element of a secondary subgroup.
• Be able to prove the chemical properties of iron and its compounds, write the reaction equations in molecular, ionic, redox form.
• To develop students' skills in compiling reaction equations involving the gland, to form students' knowledge of qualitative reactions to gland ions.
• Cultivate interest in the subject.

Equipment: iron (powder, pin, plate), sulfur, oxygen flask, hydrochloric acid, iron(II) sulfate, iron(III) chloride, sodium hydroxide, red and yellow blood salts.

DURING THE CLASSES

I. Organizational moment

II. Checking homework

III. Learning new material

1. Introduction of the teacher.

- The value of iron in life, its role in the history of civilization. One of the most common metals in the earth's crust is iron. It began to be used much later than other metals (copper, gold, zinc, lead, tin), which is most likely due to the small similarity between iron ore and metal. It was very difficult for primitive people to guess that metal can be obtained from ore, which can be successfully used in the manufacture of various items, due to the lack of tools and necessary devices for organizing such a process. Until the time when a person learned to get iron from ore and make steel and cast iron from it, a rather long time passed.
At the moment, iron ores are a necessary raw material for ferrous metallurgy, those minerals that no developed industrial country can do without. For the year, the world production of iron ores is approximately 350,000,000 tons. They are used for smelting iron (carbon content 0.2-0.4%), cast iron (2.5-4% carbon), steel (2.5-1.5% carbon) Steel has the most widespread use in industry than iron and pig iron, and therefore there is more demand for its smelting.
For smelting pig iron from iron ores, blast furnaces are used, which work on coal or coke, the remelting of steel and iron from pig iron takes place in reflective open-hearth furnaces, Bessemer converters or the Thomas method.
Ferrous metals and their alloys are of great importance in the life and development of human society. All kinds of household items and consumer goods are made of iron. For the construction of ships, aircraft, rail transport, cars, bridges, railways, various buildings, equipment and other things, hundreds of millions of tons of steel and cast iron are used. There is no branch of agriculture and industry that does not use iron and its various alloys.
Few minerals that are often found in nature, having iron in their composition, are precisely iron ore. These minerals include: brown iron ore, hematite, magnetite, and others that form large deposits and occupy vast areas.
The chemical ratio of magnetite or magnetic iron ore, which has iron - black color and a unique property - magnetism, is a compound consisting of iron oxide and ferrous oxide. In the natural environment, it can be found both in the form of granular or continuous masses, and in the form of well-formed crystals. Iron ore is richest in the content of metallic iron magnetite (up to 72%).
The largest deposits of magnetite ores in our country are located in the Urals, in the mountains High, Blagodat, Magnitnaya, in some regions of Siberia - the basin of the Angara River, Gornaya Shoria, on the territory of the Kola Peninsula.

2. Work with the class. Characteristics of iron as a chemical element

a) Position in the periodic system:

Exercise 1. Determine the position of iron in the Periodic Table?

Answer: Iron is located in the 4th major period, even row, 8th group, side group.

b) the structure of the atom:

Task 2. Sketch the composition and structure of the iron atom, the electronic formula and cells.

Answer: Fe +3 2) 8) 14) 2) metal

p = 26
e = 26
n = (56 - 26) = 30

1s 2 2s 2 2p 6 3s 2 3p 6 3d 6 4s 2

Question. What layers of iron have valence electrons? Why?

Answer. Valence electrons are located on the last and penultimate layers, since this is an element of a side subgroup.

Iron is classified as a d-element, it is part of the triad of elements - metals (Fe-Co-Ni);

c) redox properties of iron:

Question. What is an oxidizing or reducing agent? What oxidation states and valency does it exhibit?

Answer:

Fe 0 - 2e \u003d Fe +3) reducing agent
Fe 0 - 3e \u003d Fe +3
s.d. + 2, + 3; valence \u003d II and III, valence 7 - does not show;

d) iron compounds:

FeO - basic oxide
Fe (OH) 2 - insoluble base
Fe 2 O 3 - oxide with signs of amphoterism
Fe (OH) 3 - base with signs of amphoterism
Volatile hydrogen compounds are not.

e) being in nature.

Iron is the second most common metal in nature (after aluminum). In the free state, iron is found only in meteorites. The most important natural compounds:

FeO * 3HO - brown iron ore,
FeO - red iron ore,
FeO (FeO*FeO) - magnetic iron ore,
FeS - iron pyrite (pyrite)

Iron compounds are part of living organisms.

3. Characteristics of a simple iron substance

a) the structure of the molecule, the type of bond, the type of crystal lattice; (independently)

b) physical properties of iron

Iron is a silver-gray metal, has great malleability, ductility and strong magnetic properties. The density of iron is 7.87 g / cm 3, the melting point is 1539 t o C.

c) chemical properties of iron:

Iron atoms donate electrons in reactions and show oxidation states + 2, + 3 and sometimes + 6.
In reactions, iron is a reducing agent. However, at normal temperature, it does not interact even with the most active oxidizing agents (halogens, oxygen, sulfur), but when heated, it becomes active and reacts with them:

2Fe + 3Cl 2 \u003d 2FeCl 3 Iron (III) chloride
3Fe + 2O 2 \u003d Fe 2 O 3 (FeO * Fe O) Iron oxide (III)
Fe +S = FeS Iron(II) sulfide

At very high temperatures, iron reacts with carbon, silicon, and phosphorus.

3Fe + C = Fe 3 C Iron carbide (cementite)
3Fe + Si = Fe 3 Si Iron silicide
3Fe + 2P = Fe 3 P 2 Iron phosphide

Iron reacts with complex substances.
In humid air, iron quickly oxidizes (corrodes):

4Fe + 3O 2 + 6H 2 O \u003d 4Fe (OH) 3
Fe(OH) 3 ––> FeOOH + H 2 O
Rust

Iron is in the middle of the electrochemical voltage series of metals, therefore it is a metal average activity. The reducing ability of iron is less than that of alkali, alkaline earth metals and aluminum. Only at high temperatures does hot iron react with water:

3Fe + 4H 2 O \u003d Fe 3 O 4 + 4H 2

Iron reacts with dilute sulfuric and hydrochloric acids, displacing hydrogen from them:

Fe + 2HCl \u003d FeCl 2 + H 2
Fe + H 2 SO 4 \u003d FeSO 4 + H 2
Fe 0 + 2H + = Fe 2+ + H 2 0

At ordinary temperatures, iron does not interact with concentrated sulfuric acid, as it is passivated by it. When heated, concentrated sulfuric acid oxidizes iron to iron (III) sulfate:

2Fe + 6H 2 SO 4 = Fe 2 (SO 4) 3 + 3SO 2 + 6H 2 O

Dilute nitric acid oxidizes iron to iron(III) nitrate:

Fe + 4HNO 3 \u003d Fe (NO 3) 3 + NO + 2H 2 O

Concentrated nitric acid passivates the iron.

From salt solutions, iron displaces metals that are located to the right of it in the electrochemical series of voltages:

Fe + CuSO 4 \u003d FeSO 4 + Cu,

d) the use of iron (independently)

e) receiving (together with students)

In industry, iron is obtained by reducing it from iron ores with carbon (coke) and carbon monoxide (II) in blast furnaces.
The chemistry of the domain process is as follows:

C+O=CO
CO + C = 2CO
3Fe 2 O 3 + CO \u003d 2Fe 3 O 4 + CO 2
Fe 3 O 4 + CO \u003d 3FeO + CO 2
FeO + CO \u003d Fe + CO 2

4. Iron compounds

Chemical properties of these compounds.

Addition. Iron(II) compounds are unstable, they can oxidize and turn into iron(III) compounds

Fe +2 Cl 2 + Cl 2 \u003d Fe +3 Cl 3 make up redox houses
Fe +2 (OH) + H 2 O + O 2 \u003d Fe +3 (OH) 3 schemes, equalize.

Chemical properties of these compounds

Also, a qualitative reaction to Fe + 2 is the reaction of iron (II) salts with a substance called red blood salt K 3 - this is a complex compound.

3FeCl + 2K 3 \u003d Fe 3)