Active metals with water. Interaction of metals with non-metals. Examples of reactions of interaction of metals with acids

Properties of metals.

1. Basic properties of metals.

The properties of metals are divided into physical, chemical, mechanical and technological.

Physical properties include: color, specific gravity, fusibility, electrical conductivity, magnetic properties, thermal conductivity, expansion when heated.

To chemical - oxidizability, solubility and corrosion resistance.

To mechanical - strength, hardness, elasticity, viscosity, plasticity.

To technological - hardenability, fluidity, malleability, weldability, machinability.

1. Physical and chemical properties.

Colour. Metals are opaque, i.e. do not let light through, and in this reflected light, each metal has its own special shade - color.

Of the technical metals, only copper (red) and its alloys are colored. The color of other metals ranges from steel gray to silvery white. The thinnest films of oxides on the surface of metal products give them additional colors.

Specific gravity. The weight of one cubic centimeter of a substance, expressed in grams, is called specific gravity.

According to the specific gravity, light metals and heavy metals are distinguished. Of the technical metals, magnesium is the lightest (specific gravity 1.74), the heaviest is tungsten (specific gravity 19.3). The specific gravity of metals depends to some extent on the way they are produced and processed.

Fusibility. The ability to change from solid to liquid when heated is the most important property metals. When heated, all metals pass from a solid state to a liquid state, and when a molten metal is cooled, from a liquid state to a solid state. The melting point of technical alloys has not one specific melting point, but a range of temperatures, sometimes quite significant.

Electrical conductivity. Conductivity is the transfer of electricity by free electrons. The electrical conductivity of metals is thousands of times higher than the electrical conductivity of non-metallic bodies. As the temperature rises, the electrical conductivity of metals decreases, and as the temperature decreases, it increases. When approaching absolute zero(- 273 0 C) the electrical conductivity of infinitely metals ranges from +232 0 (tin) to 3370 0 (tungsten). Most increases (resistance drops to near zero).

The electrical conductivity of alloys is always lower than the electrical conductivity of one of the components that make up the alloys.

Magnetic properties. Only three metals are clearly magnetic (ferromagnetic): iron, nickel, and cobalt, as well as some of their alloys. When heated to certain temperatures, these metals also lose their magnetic properties. Some iron alloys are not ferromagnetic even at room temperature. All other metals are divided into paramagnetic (attracted by magnets) and diamagnetic (repelled by magnets).

Thermal conductivity. Thermal conductivity is the transfer of heat in a body from a hotter place to a less heated place without visible movement of the particles of this body. The high thermal conductivity of metals allows them to be heated and cooled quickly and evenly.

Of the technical metals, copper has the highest thermal conductivity. The thermal conductivity of iron is much lower, and the thermal conductivity of steel varies depending on the content of components in it. As the temperature rises, the thermal conductivity decreases, and as the temperature decreases, it increases.

Heat capacity. Heat capacity is the amount of heat required to raise the temperature of a body by 10.

The specific heat capacity of a substance is the amount of heat in kilograms - calories, which must be reported to 1 kg of a substance in order to raise its temperature by 1 0.

The specific heat capacity of metals in comparison with other substances is small, which makes it relatively easy to heat them to high temperatures.

Expansion when heated. The ratio of the increment in the length of the body when it is heated by 1 0 to its original length is called the coefficient of linear expansion. For different metals, the coefficient of linear expansion varies widely. For example, tungsten has a linear expansion coefficient of 4.0·10 -6 , and lead 29.5 ·10 -6 .

Corrosion resistance. Corrosion is the destruction of a metal due to its chemical or electrochemical interaction with the external environment. An example of corrosion is the rusting of iron.

High corrosion resistance (corrosion resistance) is an important natural property of some metals: platinum, gold and silver, which is why they are called noble. Nickel and other non-ferrous metals also resist corrosion well. Ferrous metals corrode more strongly and faster than non-ferrous metals.

2. Mechanical properties.

Strength. The strength of a metal is its ability to resist the action of external forces without collapsing.

Hardness. Hardness is the ability of a body to resist the penetration of another, more solid body.

Elasticity. The elasticity of a metal is its property to restore its shape after the termination of the action of external forces that caused a change in shape (deformation.)

Viscosity. Toughness is the ability of a metal to resist rapidly increasing (shock) external forces. Viscosity is the opposite property of brittleness.

Plastic. Plasticity is the property of a metal to be deformed without destruction under the action of external forces and to retain a new shape after the cessation of the forces. Plasticity is a property that is the opposite of elasticity.

In table. 1 shows the properties of technical metals.

Table 1.

Properties of technical metals.

metal name	Specific gravity (density) gcm 3	Melting point 0 С	Brinell hardness	Tensile strength (tensile strength) kgmm 2	Relative extension %	Relative contraction of the cross section %
AluminumTungstenIronCobaltMagnesiumManganeseCopperNickelTinLeadChromiumZinc	2,7 19,3 7,87 8,9 1,74 7,44 8,84 8,9 7,3 11,34 7,14 7,14	658 3370 1530 1490 651 1242 1083 1452 232 327 1550 419	20-37 160 50 125 25 20 35 60 5-10 4-6 108 30-42	8-11 110 25-33 70 17-20 Fragile22 40-50 2-4 1,8 Fragile11,3-15	40 - 21-55 3 15 Fragile60 40 40 50 Fragile5-20	85 - 68-55 - 20 Fragile75 70 74 100 Fragile-

3. Significance of the properties of metals.

Mechanical properties. The first requirement for any product is sufficient strength.

Metals have a higher strength compared to other materials, so the loaded parts of machines, mechanisms and structures are usually made of metals.

Many products, in addition to general strength, must also have special properties characteristic of the operation of this product. For example, cutting tools must have high hardness. For the manufacture of other cutting tools, tool steels and alloys are used.

For the manufacture of springs and springs, special steels and alloys with high elasticity are used.

Ductile metals are used in cases where parts are subjected to shock loading during operation.

The plasticity of metals makes it possible to process them by pressure (forging, rolling).

physical properties. In aircraft, auto and carriage building, the weight of parts is often the most important characteristic, so aluminum and especially magnesium alloys are indispensable here. Specific strength (the ratio of tensile strength to specific gravity) for some alloys, such as aluminum, is higher than for mild steel.

Fusibility used to obtain castings by pouring molten metal into molds. Low-melting metals (such as lead) are used as a quenching medium for steel. Some complex alloys have such a low melting point that they melt in hot water. Such alloys are used for casting printing matrices, in devices that serve to protect against fires.

Metals with high electrical conductivity(copper, aluminum) are used in electrical engineering, for the construction of power lines, and alloys with high electrical resistance - for incandescent lamps, electric heaters.

Magnetic properties metals play a primary role in electrical engineering (dynamos, motors, transformers), for communication devices (telephone and telegraph sets) and are used in many other types of machines and devices.

Thermal conductivity metals makes it possible to produce their physical properties. Thermal conductivity is also used in the production of soldering and welding of metals.

Some metal alloys have linear expansion coefficient, close to zero; such alloys are used for the manufacture of precision instruments, radio tubes. The expansion of metals must be taken into account when constructing long structures such as bridges. It should also be borne in mind that two parts made of metals with different coefficients of expansion and fastened together can bend and even break when heated.

Chemical properties. Corrosion resistance is especially important for products operating in highly oxidizing environments (grate grates, parts of chemical machines and devices). To achieve high corrosion resistance, special stainless, acid-resistant and heat-resistant steels are produced, and protective coatings are also used.

Metals (from lat. metallum - mine, mine) - a group of elements, in the form simple substances with characteristic metallic properties, such as high thermal and electrical conductivity, positive temperature coefficient of resistance, high ductility and metallic luster.

Of the 118 chemical elements discovered at the moment (of which not all are officially recognized), metals include:

• 6 elements in the alkali metal group,
• 6 in the group of alkaline earth metals,
• 38 in the transition metal group,
• 11 in the group of light metals,
• 7 in the group of semimetals,
• 14 in the group of lanthanides + lanthanum,
• 14 in the group of actinides (physical properties have not been studied for all elements) + actinium,
• outside certain groups of beryllium and magnesium.

Thus, 96 elements out of all those discovered may belong to metals.

In astrophysics, the term "metal" can have a different meaning and refer to all chemical elements heavier than helium

Characteristic properties of metals

1. Metallic luster (characteristic not only for metals: non-metals iodine and carbon in the form of graphite also have it)
2. Good electrical conductivity
3. Possibility of light machining
4. High density (usually metals are heavier than non-metals)
5. High melting point (exceptions: mercury, gallium and alkali metals)
6. Great thermal conductivity
7. In reactions, they are most often reducing agents.

Physical properties of metals

All metals (except mercury and, conditionally, France) are in a solid state under normal conditions, but they have different hardness. Below is the hardness of some metals on the Mohs scale.

Melting points pure metals range from -39 °C (mercury) to 3410 °C (tungsten). The melting point of most metals (with the exception of alkalis) is high, but some "normal" metals, such as tin and lead, can be melted on a conventional electric or gas stove.

Depending on the density, metals are divided into light (density 0.53 ÷ 5 g / cm³) and heavy (5 ÷ 22.5 g / cm³). The lightest metal is lithium (density 0.53 g/cm³). It is currently impossible to name the heaviest metal, since the densities of osmium and iridium - the two heaviest metals - are almost equal (about 22.6 g / cm³ - exactly twice the density of lead), and it is extremely difficult to calculate their exact density: for this you need completely clean metals, because any impurities reduce their density.

Most metals plastic, that is, a metal wire can be bent, and it will not break. This is due to the displacement of the layers of metal atoms without breaking the bond between them. The most plastic are gold, silver and copper. Gold can be used to make foil with a thickness of 0.003 mm, which is used for gilding products. However, not all metals are plastic. Zinc or tin wire crunches when bent; manganese and bismuth do not bend at all during deformation, but immediately break. Plasticity also depends on the purity of the metal; Thus, very pure chromium is very ductile, but contaminated with even minor impurities, it becomes brittle and harder. Some metals such as gold, silver, lead, aluminium, osmium can grow together, but this can take decades.

All metals are good conduct electric current; This is due to the presence in them crystal lattices mobile electrons moving under the influence of electric field. Silver, copper and aluminum have the highest electrical conductivity; for this reason, the last two metals are most often used as a material for wires. Sodium also has a very high electrical conductivity; attempts are known to use sodium conductors in the form of thin-walled stainless steel tubes filled with sodium in experimental equipment. Due to the low specific gravity of sodium, with equal resistance, sodium "wires" are much lighter than copper and even somewhat lighter than aluminum.

The high thermal conductivity of metals also depends on the mobility of free electrons. Therefore, the series of thermal conductivities is similar to the series of electrical conductivities and the best conductor of heat, like electricity, is silver. Sodium also finds use as a good conductor of heat; It is widely known, for example, the use of sodium in the valves of automobile engines to improve their cooling.

Colour most metals are approximately the same - light gray with a bluish tint. Gold, copper, and cesium are yellow, red, and light yellow, respectively.

Chemical properties of metals

At the external electronic level, most metals have a small number of electrons (1-3), so they act as reducing agents in most reactions (that is, they “give away” their electrons)

Reactions with simple substances

• All metals react with oxygen except gold and platinum. The reaction with silver occurs at high temperatures, but silver(II) oxide is practically not formed, since it is thermally unstable. Depending on the metal, the output may be oxides, peroxides, superoxides:

lithium oxide

sodium peroxide

potassium superoxide

To obtain oxide from peroxide, the peroxide is reduced with a metal:

With medium and low-active metals, the reaction occurs when heated:

• Only the most active metals react with nitrogen, only lithium interacts at room temperature, forming nitrides:

When heated:

• All metals react with sulfur except gold and platinum:

Iron reacts with sulfur when heated to form sulfide:

• Only the most active metals react with hydrogen, that is, metals of groups IA and IIA, except for Be. The reactions are carried out when heated, and hydrides are formed. In reactions, the metal acts as a reducing agent, the oxidation state of hydrogen is −1:

• Only the most active metals react with carbon. In this case, acetylenides or methanides are formed. Acetylides, when interacting with water, give acetylene, methanides - methane.

Metals differ greatly in their chemical activity. The chemical activity of a metal can be roughly judged by its position in.

The most active metals are located at the beginning of this row (on the left), the most inactive - at the end (on the right).
Reactions with simple substances. Metals react with non-metals to form binary compounds. The reaction conditions, and sometimes their products, vary greatly for different metals.
For example, alkali metals actively react with oxygen (including in air) at room temperature to form oxides and peroxides.

4Li + O 2 = 2Li 2 O;
2Na + O 2 \u003d Na 2 O 2

Intermediate activity metals react with oxygen when heated. In this case, oxides are formed:

2Mg + O 2 \u003d t 2MgO.

Inactive metals (for example, gold, platinum) do not react with oxygen and, therefore, practically do not change their luster in air.
Most metals, when heated with sulfur powder, form the corresponding sulfides:

Reactions with complex substances. Compounds of all classes react with metals - oxides (including water), acids, bases and salts.
Active metals react violently with water at room temperature:

2Li + 2H 2 O \u003d 2LiOH + H 2;
Ba + 2H 2 O \u003d Ba (OH) 2 + H 2.

The surface of metals such as magnesium and aluminium, for example, is protected by a dense film of the respective oxide. This prevents the reaction with water. However, if this film is removed or its integrity is violated, then these metals also actively react. For example, powdered magnesium reacts with hot water:

Mg + 2H 2 O \u003d 100 ° C Mg (OH) 2 + H 2.

At elevated temperatures, less active metals also react with water: Zn, Fe, Mil, etc. In this case, the corresponding oxides are formed. For example, when water vapor is passed over hot iron shavings, the following reaction occurs:

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

Metals in the activity series up to hydrogen react with acids (except HNO 3) to form salts and hydrogen. Active metals (K, Na, Ca, Mg) react with acid solutions very violently (at high speed):

Ca + 2HCl \u003d CaCl 2 + H 2;
2Al + 3H 2 SO 4 \u003d Al 2 (SO 4) 3 + 3H 2.

Inactive metals are often practically insoluble in acids. This is due to the formation of an insoluble salt film on their surface. For example, lead, which is in the activity series up to hydrogen, practically does not dissolve in dilute sulfuric and hydrochloric acids due to the formation of a film of insoluble salts (PbSO 4 and PbCl 2) on its surface.

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Interaction of metals with simple oxidizing agents. The ratio of metals to water, aqueous solutions of acids, alkalis and salts. The role of the oxide film and oxidation products. Interaction of metals with nitric and concentrated sulfuric acids.

Metals include all s-, d-, f-elements, as well as p-elements located in the lower part periodic system from the diagonal drawn from boron to astatine. In simple substances of these elements, a metallic bond is realized. Metal atoms have few electrons in the outer electron shell, in the amount of 1, 2, or 3. Metals exhibit electropositive properties and have low electronegativity, less than two.

Metals are inherent characteristics. This is solids, heavier than water, with a metallic sheen. Metals have high thermal and electrical conductivity. They are characterized by the emission of electrons under the influence of various external influences: irradiation with light, during heating, during rupture (exoelectronic emission).

The main feature of metals is their ability to donate electrons to atoms and ions of other substances. Metals are reducing agents in the vast majority of cases. And this is their characteristic chemical property. Consider the ratio of metals to typical oxidizing agents, which include simple substances - non-metals, water, acids. Table 1 provides information on the ratio of metals to simple oxidizing agents.

Table 1

The ratio of metals to simple oxidizing agents

All metals react with fluorine. The exceptions are aluminum, iron, nickel, copper, zinc in the absence of moisture. These elements, when reacting with fluorine, initially form fluoride films that protect the metals from further reaction.

Under the same conditions and reasons, iron is passivated in reaction with chlorine. In relation to oxygen, not all, but only a number of metals form dense protective films of oxides. In the transition from fluorine to nitrogen (table 1), the oxidative activity decreases and therefore all more metals are not oxidized. For example, only lithium and alkaline earth metals react with nitrogen.

The ratio of metals to water and aqueous solutions of oxidizing agents.

AT aqueous solutions the reducing activity of a metal is characterized by the value of its standard redox potential. From the entire range of standard redox potentials, a series of metal voltages is distinguished, which is indicated in table 2.

table 2

Row stress metals

Oxidizing agent	Electrode process equation	Standard electrode potential φ 0, V	Reducing agent	Conditional activity of reducing agents
Li+	Li + + e - = Li	-3,045	Li	Active
Rb+	Rb + + e - = Rb	-2,925	Rb	Active
K+	K + + e - = K	-2,925	K	Active
Cs+	Cs + + e - = Cs	-2,923	Cs	Active
Ca2+	Ca 2+ + 2e - = Ca	-2,866	Ca	Active
Na+	Na + + e - = Na	-2,714	Na	Active
Mg2+	Mg 2+ +2 e - \u003d Mg	-2,363	mg	Active
Al 3+	Al 3+ + 3e - = Al	-1,662	Al	Active
Ti 2+	Ti 2+ + 2e - = Ti	-1,628	Ti	Wed activity
Mn2+	Mn 2+ + 2e - = Mn	-1,180	Mn	Wed activity
Cr2+	Cr 2+ + 2e - = Cr	-0,913	Cr	Wed activity
H2O	2H 2 O+ 2e - \u003d H 2 + 2OH -	-0,826	H 2 , pH=14	Wed activity
Zn2+	Zn 2+ + 2e - = Zn	-0,763	Zn	Wed activity
Cr3+	Cr 3+ +3e - = Cr	-0,744	Cr	Wed activity
Fe2+	Fe 2+ + e - \u003d Fe	-0,440	Fe	Wed activity
H2O	2H 2 O + e - \u003d H 2 + 2OH -	-0,413	H 2 , pH=7	Wed activity
CD 2+	Cd 2+ + 2e - = Cd	-0,403	CD	Wed activity
Co2+	Co 2+ +2 e - \u003d Co	-0,227	co	Wed activity
Ni2+	Ni 2+ + 2e - = Ni	-0,225	Ni	Wed activity
sn 2+	Sn 2+ + 2e - = Sn	-0,136	sn	Wed activity
Pb 2+	Pb 2+ + 2e - = Pb	-0,126	Pb	Wed activity
Fe3+	Fe 3+ + 3e - \u003d Fe	-0,036	Fe	Wed activity
H+	2H + + 2e - =H 2		H 2 , pH=0	Wed activity
Bi 3+	Bi 3+ + 3e - = Bi	0,215	Bi	Small active
Cu2+	Cu 2+ + 2e - = Cu	0,337	Cu	Small active
Cu+	Cu + + e - = Cu	0,521	Cu	Small active
Hg 2 2+	Hg 2 2+ + 2e - = Hg	0,788	Hg 2	Small active
Ag+	Ag + + e - = Ag	0,799	Ag	Small active
Hg2+	Hg 2+ + 2e - \u003d Hg	0,854	hg	Small active
Pt 2+	Pt 2+ + 2e - = Pt	1,2	Pt	Small active
Au 3+	Au 3+ + 3e - = Au	1,498	Au	Small active
Au +	Au++e-=Au	1,691	Au	Small active

In this series of voltages, the values ​​of the electrode potentials of the hydrogen electrode in acidic (рН=0), neutral (рН=7), alkaline (рН=14) media are also given. The position of a particular metal in a series of stresses characterizes its ability to redox interactions in aqueous solutions under standard conditions. Metal ions are oxidizing agents and metals are reducing agents. The further the metal is located in the series of voltages, the stronger the oxidizing agent in an aqueous solution are its ions. The closer the metal is to the beginning of the row, the stronger the reducing agent it is.

Metals are able to displace each other from salt solutions. The direction of the reaction is determined in this case by their mutual position in the series of voltages. It should be borne in mind that active metals displace hydrogen not only from water, but also from any aqueous solution. Therefore, the mutual displacement of metals from solutions of their salts occurs only in the case of metals located in the series of voltages after magnesium.

All metals are divided into three conditional groups, which is reflected in the following table.

Table 3

Conditional division of metals

Interaction with water. The oxidizing agent in water is the hydrogen ion. Therefore, only those metals can be oxidized by water, the standard electrode potentials of which are lower than the potential of hydrogen ions in water. It depends on the pH of the medium and is

φ \u003d -0.059 pH.

In a neutral environment (рН=7) φ = -0.41 V. The nature of the interaction of metals with water is presented in Table 4.

Metals from the beginning of the series, having a potential much more negative than -0.41 V, displace hydrogen from water. But already magnesium displaces hydrogen only from hot water. Normally, metals located between magnesium and lead do not displace hydrogen from water. Oxide films are formed on the surface of these metals, which have a protective effect.

Table 4

Interaction of metals with water in a neutral medium

Interaction of metals with hydrochloric acid.

The oxidizing agent in hydrochloric acid is the hydrogen ion. The standard electrode potential of a hydrogen ion is zero. Therefore, all active metals and metals of intermediate activity must react with the acid. Only lead exhibits passivation.

Table 5

The interaction of metals with hydrochloric acid

Copper can be dissolved in very concentrated hydrochloric acid, despite the fact that it belongs to low-active metals.

The interaction of metals with sulfuric acid occurs differently and depends on its concentration.

Reaction of metals with dilute sulfuric acid. Interaction with dilute sulfuric acid is carried out in the same way as with hydrochloric acid.

Table 6

Reaction of metals with dilute sulfuric acid

Diluted sulfuric acid oxidizes with its hydrogen ion. It interacts with those metals whose electrode potentials are lower than those of hydrogen. Lead does not dissolve in sulfuric acid at a concentration below 80%, since the PbSO 4 salt formed during the interaction of lead with sulfuric acid is insoluble and creates a protective film on the metal surface.

Interaction of metals with concentrated sulfuric acid.

In concentrated sulfuric acid, sulfur in the +6 oxidation state acts as an oxidizing agent. It is part of the sulfate ion SO 4 2-. Therefore, concentrated acid oxidizes all metals whose standard electrode potential is less than that of the oxidizing agent. Highest value The electrode potential in electrode processes involving the sulfate ion as an oxidizing agent is 0.36 V. As a result, some low-active metals also react with concentrated sulfuric acid.

For metals of medium activity (Al, Fe), passivation takes place due to the formation of dense oxide films. Tin is oxidized to the tetravalent state with the formation of tin (IV) sulfate:

Sn + 4 H 2 SO 4 (conc.) \u003d Sn (SO 4) 2 + 2SO 2 + 2H 2 O.

Table 7

Interaction of metals with concentrated sulfuric acid

Lead oxidizes to the divalent state with the formation of soluble lead hydrosulfate. Mercury dissolves in hot concentrated sulfuric acid to form mercury (I) and mercury (II) sulfates. Even silver dissolves in boiling concentrated sulfuric acid.

It should be borne in mind that the more active the metal, the deeper the degree of reduction of sulfuric acid. With active metals, the acid is reduced mainly to hydrogen sulfide, although other products are also present. for example

Zn + 2H 2 SO 4 \u003d ZnSO 4 + SO 2 + 2H 2 O;

3Zn + 4H 2 SO 4 = 3ZnSO 4 + S↓ + 4H 2 O;

4Zn + 5H 2 SO 4 \u003d 4ZnSO 4 \u003d 4ZnSO 4 + H 2 S + 4H 2 O.

Interaction of metals with dilute nitric acid.

In nitric acid, nitrogen in the +5 oxidation state acts as an oxidizing agent. The maximum value of the electrode potential for the nitrate ion of dilute acid as an oxidizing agent is 0.96 V. Due to such a large value, nitric acid is a stronger oxidizing agent than sulfuric acid. This is evident from the fact that nitric acid oxidizes silver. The acid is reduced the deeper, the more active the metal and the more dilute the acid.

Table 8

Reaction of metals with dilute nitric acid

Interaction of metals with concentrated nitric acid.

Concentrated nitric acid is usually reduced to nitrogen dioxide. The interaction of concentrated nitric acid with metals is presented in table 9.

When using acid in deficiency and without stirring, active metals reduce it to nitrogen, and metals of medium activity to carbon monoxide.

Table 9

Interaction of concentrated nitric acid with metals

Interaction of metals with alkali solutions.

Metals cannot be oxidized by alkalis. This is due to the fact that alkali metals are strong reducing agents. Therefore, their ions are the weakest oxidizing agents and do not exhibit oxidizing properties in aqueous solutions. However, in the presence of alkalis, the oxidizing effect of water is manifested to a greater extent than in their absence. Due to this, in alkaline solutions, metals are oxidized by water to form hydroxides and hydrogen. If the oxide and hydroxide are amphoteric compounds, then they will dissolve in an alkaline solution. As a result, metals that are passive in pure water interact vigorously with alkali solutions.

Table 10

Interaction of metals with alkali solutions

The dissolution process is presented in the form of two stages: the oxidation of the metal with water and the dissolution of the hydroxide:

Zn + 2HOH \u003d Zn (OH) 2 ↓ + H 2;

Zn (OH) 2 ↓ + 2NaOH \u003d Na 2.

First of all, it should be remembered that metals are generally divided into three groups:

1) Active metals: These metals include all alkali metals, alkaline earth metals, as well as magnesium and aluminium.

2) Metals of medium activity: these include metals located between aluminum and hydrogen in the activity series.

3) Inactive metals: metals located in the activity series to the right of hydrogen.

First of all, you need to remember that low-active metals (that is, those located after hydrogen) do not react with water under any conditions.

Alkali and alkaline earth metals react with water under any conditions (even at ordinary temperature and in the cold), while the reaction is accompanied by the evolution of hydrogen and the formation of metal hydroxide. For example:

2Na + 2H 2 O \u003d 2NaOH + H 2

Ca + 2H 2 O \u003d Ca (OH) 2 + H 2

Magnesium, due to the fact that it is covered with a protective oxide film, reacts with water only when it is boiled. When heated in water, the oxide film consisting of MgO is destroyed and the magnesium under it begins to react with water. In this case, the reaction is also accompanied by the evolution of hydrogen and the formation of metal hydroxide, which, however, is insoluble in the case of magnesium:

Mg + 2H 2 O \u003d Mg (OH) 2 ↓ + H 2

Aluminum, like magnesium, is covered with a protective oxide film, but in this case it cannot be destroyed by boiling. To remove it, either mechanical cleaning (with some kind of abrasive) or its chemical destruction with alkali, solutions of mercury salts or ammonium salts are required:

2Al + 6H 2 O \u003d 2Al (OH) 3 + 3H 2

Metals of medium activity react with water only when it is in a state of superheated water vapor. In this case, the metal itself must be heated to a red-hot temperature (about 600-800 ° C). Unlike active metals, metals of intermediate activity, when reacting with water, form metal oxides instead of hydroxides. The reduction product in this case is hydrogen:

Zn + H 2 O \u003d ZnO + H 2

3Fe + 4H 2 O = Fe 3 O 4 + 4H 2 or

Fe + H 2 O \u003d FeO + H 2 (depending on the degree of heating)