LABORATORY WORK

Goal of the work– familiarization with the most important classes of inorganic compounds: oxides, hydroxides, salts, methods of their preparation and properties.

THEORETICAL PART

To date, about 300 thousand inorganic compounds are known. They can be divided into three major classes: oxides, hydroxides and salts.

OXIDES - products of the combination of elements with oxygen.

Oxides can be obtained by the reaction of combining an element with oxygen:

2Mg + O 2 \u003d MgO,

4P + 5O 2 \u003d 2 P 2 O 5

or the decomposition reaction of a complex substance:

CaCO 3 \u003d CaO + CO 2,

2 Zn(NO 3) 2 \u003d 2 ZnO + 4 NO 2 + O 2.

There are salt-forming and non-salt-forming oxides, as well as peroxides.

Salt-forming oxides subdivided into basic, acidic and amphoteric.

Basic oxides form alkali metals (Li, Na, K, Rb, Cs, Fr), alkaline earth metals (Mg, Ca, Sr, Ba) and metals with a variable oxidation state, located in the PTM side subgroups in their lowest oxidation states +1, +2 (for example: Zn, Cd, Hg, Cr, Mn, etc.). Their hydroxides are bases.

Bases that are highly soluble in water alkali metals are called alkalis. They can be obtained by dissolving the corresponding oxides in water, for example:

Na 2 O + H 2 O \u003d 2NaOH

Hydroxides (bases) of alkaline earth metals (Mg, Ca, Sr, Ba) are also formed when the corresponding oxides are dissolved in water, however, all of them, except for barium hydroxide Ba (OH) 2, are slightly or sparingly soluble.

Basic oxides react with acidic oxides and acids to form salts:

CaO + CO 2 \u003d CaCO 3;

CuO + 2 HCl \u003d CuCl 2 + H 2 O.

Acid oxides form non-metals (B, C, N, P, S, Cl, etc.), as well as metals with a variable degree of oxidation, located in the side subgroups of PTM, in their higher degrees oxidation +5, +6, +7 (for example: V, Cr, Mn, etc.).

Acid oxide hydrates are acids that can be obtained by reacting acid oxides with water:

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

Acid oxides react with basic oxides and bases:

SO 2 + Na 2 O \u003d Na 2 SO 3;

N 2 O 5 + 2 NaOH \u003d 2 NaNO 3 + H 2 O.

Amphoteric oxides form metals of the main subgroups of PTM (for example: Al 3+, Sn 2+, Pb 2+, etc.) and metals with a variable degree of oxidation, located in the side subgroups of PTM, in medium oxidation states +3, +4 (Cr, Mn, and etc.). Their hydroxides (hydrates) exhibit both basic and acidic properties. Amphoteric oxides react with both acids and bases:

Cr 2 O 3 + 6 HCl = 2 CrCl 3 + 3 H 2 O;

Cr 2 O 3 + 2 NaOH = 2 NaCrO 2 + H 2 O

. Non-salt-forming oxides a little (for example, CO, NO, N 2 O), they do not form salts with either acids or bases.

Peroxides - derivatives of hydrogen peroxide (H 2 O 2). Alkali metal peroxides (Li, Na, K, Rb, Cs) and alkaline earth metals(Ca, Sr, Ba) refer to salts of hydrogen peroxide. In them, oxygen atoms are interconnected by a covalent bond (for example, K 2 O 2: K - O - O - K) and easily decompose with the elimination of atomic oxygen, therefore peroxides are strong oxidizing agents

HYDROXIDES - products of the compound are clear hydroxides (bases), acidic oxides with water. There are basic hydroxides (acids) and amphoteric hydroxides (ampholytes).

Basic hydroxides (bases) dissociate in solution into metal ions and hydroxide ions:

NaOH ↔ Na + + OH ‾ .

The acidity of a base is determined by the number of hydroxide ions OH‾, which are called functional groups grounds. According to the number of functional groups, one-acid (for example: NaOH), two-acid (for example: Ca (OH) 2), three-acid (for example: Al (OH) 3) bases are distinguished.

Polyacid bases dissociate in steps:

Ca(OH) 2 ↔ (CaOH) + + OH ‾ , (CaOH) + ↔ Ca 2+ + OH ‾ .

Aqueous solutions of highly soluble bases (alkalis) change the color of indicators . In alkaline solutions, violet litmus turns blue, colorless phenolphthalein turns crimson, and methyl orange turns yellow.

Bases react with acids to form salts and water:

NaOH + HCl \u003d NaCl + H 2 O.

If the base and acid are taken in equimolar ratios, then the medium becomes neutral, and such a reaction is called a neutralization reaction.

Many water-insoluble bases decompose when heated:

Cu (OH) 2 \u003d CuO + H 2 O.

Alkalis are obtained by dissolving oxides in water:

K 2 O + H 2 O \u003d 2 KOH.

Water-insoluble bases can be obtained by the action of alkalis on soluble metal salts:

CuSO 4 + 2 NaOH \u003d Cu (OH) 2 ↓ + Na 2 SO 4.

Acid hydroxides (acids) dissociate into hydrogen ions H + (more precisely, hydronium ions H 3 O +) and an acid residue:

HCl ↔ H + + Cl ‾ .

The basicity of an acid is determined by the number of hydrogen ions, which are called functional groups for the acid, for example: HCl is monobasic, H 2 SO 4 is dibasic, H 3 PO 4 is tribasic.

Polybasic acids dissociate in steps:

H 2 SO 3 ↔ H + + HSO 3 ‾; HSO 3 ‾ ↔ H + + SO 3 ‾ .

There are oxygen-free acids(HCl, HI, H 2 S, HCN, etc.) and oxygen-containing (HNO 3, H 2 SO 4, H 2 SO 3, H 3 PO 4, etc.).

In acid solutions, litmus turns red, methyl orange turns pink, and phenolphthalein remains colorless.

Acids are obtained by dissolving acid oxides in water:

P 2 O 5 + 3 H 2 O \u003d 2 H 3 PO 4

or by the reaction of the exchange of a salt with an acid:

Ca 3 (PO 4) 2 + 3 H 2 SO 4 \u003d 3 CaSO 4 + 2 H 3 PO 4.

Amphoteric hydroxides(A mfolity) are hydroxides that exhibit both basic and acidic properties in reactions. These include Be (OH) 2, Al (OH) 3, Zn (OH) 2, Cr (OH) 3, etc. Amphoteric hydroxides react with bases as acids, with acids as bases:

Cr(OH) 3 + 3 HCl = CrCl 3 + 3 H 2 O;

Cr (OH) 3 + 3 NaOH \u003d Na 3.

SALTs during dissociation form metal ions (cations) (or ammonium ion NH 4 +) and ions (anions) of acid residues:

Na 2 SO 4 ↔ 2 Na + + SO 4 2 ‾ ,

NH 4 NO 3 ↔ NH 4 + + NO 3 ‾ .

Distinguish between medium, acidic and basic salts.

Medium salts can be considered as products of complete replacement of hydrogen atoms in the acid by metal atoms or hydroxo groups of the base by acidic residues: NaCl, K 2 SO 4 , AlPO 4 .

H 2 SO 4 + Ba(OH) 2 = BaSO 4 + 2H 2 O

KOH + HNO 3 \u003d KNO 3 + H 2 O

Medium salts dissociate into metal cations and anions of acid residues:

AlPO 4 ↔ Al 3+ + PO 4 3 ‾.

Acid salts(hydrosalts) are products of incomplete replacement of hydrogen atoms of polybasic acids with metal atoms: NaHSO 4, Al (H 2 PO 4) 3, KHCO 3 ^

H 2 SO 4 + NaOH = NaHSO 4 + H 2 O

The dissociation of an acid salt is expressed by the equation:

Al(H 2 PO 4) 3 ↔ Al 3+ + 3 (H 2 PO 4) ‾ .

Anion (H 2 PO 4) ‾ undergoes further dissociation to a small extent.

saltsBasic(hydroxysalts) are products of incomplete replacement of the hydroxo groups of a polyacid base with acidic residues: AlOHSO 4 , MgOHCl, (CuOH) 2 SO 4 .

Mg(OH) 2 + HCI \u003d MgOHCI + H 2 O

The dissociation of the basic salt is expressed by the equation:

AlOHSO 4 ↔ (AlOH) 2 + + SO 4 2‾.

The cation (AlOH) 2+ undergoes further dissociation to a small extent.

Medium salts can be obtained in many ways:

the combination of metal and non-metal: 2 Na + Cl 2 = 2 NaCl;

the combination of basic and acidic oxides: CaO + CO 2 \u003d CaCO 3;

by displacing hydrogen or a less active metal with an active metal:

Zn + 2 HCl \u003d H 2 + ZnCl 2,

Zn + CuSO 4 \u003d ZnSO 4 + Cu;

neutralization reaction: NaOH + HCl = NaCl + H 2 O;

exchange reaction: Ba (NO 3) 2 + Na 2 SO 4 \u003d BaSO 4 + 2 NaNO 3, etc.

Acid salts can be obtained in an acidic environment:

NaOH + H 2 SO 4 (excess) = NaHSO 4 + H 2 O;

Na 3 PO 4 + 2 H 3 PO 4 (excess) = 3 NaH 2 PO 4.

Basic salts can be obtained in alkaline environment:

H 2 SO 4 + 2 Cu (OH) 2 (excess) \u003d (CuOH) 2 SO 4 + Na 2 SO 4,

2 CuSO 4 + 2 NaOH (lack) = (CuOH) 2 SO 4 + Na 2 SO 4

Acid salts with an excess of alkali and basic salts with an excess of acid turn into medium salts: NaHSO 4 + NaOH (excess) \u003d Na 2 SO 4 + H 2 O,

(CuOH) 2 SO 4 + H 2 SO 4 (excess) = 2 CuSO 4 + 2 H 2 O.

Many metals are characterized by complex compounds that dissociate in solution as strong electrolytes, forming stable complex ions:

CuSO 4 + 8NH 4 OH (excess) = (OH) 2 + SO 4 + 8 H 2 O.

The degree of dissociation of complex compounds is insignificant:

(OH) 2 ↔ 2+ + 2OH ‾

SO 4 ↔ 2+ + SO 4 2‾

Complex compounds many d - metals are colored, which allows them to be used in analytical practice for the detection of metal ions.

There are also double salts formed by different metals and one acid residue (KAl (SO 4) 2) and mixed, formed by one metal and different acid residues (CaClOCl).

basic or acid.

PRACTICAL PART

PREPARATION AND PROPERTIES OF OXIDES

When studying the material of the previous paragraphs, you have already become acquainted with some substances. So, for example, a hydrogen gas molecule consists of two atoms of the chemical element hydrogen -

Simple substances are substances that contain atoms of the same type.

Simple substances, from among the substances known to you, include: oxygen, graphite, sulfur, nitrogen, all metals: iron, copper, aluminum, gold, etc. Sulfur is made up of only atoms of the chemical element sulfur, while graphite is made up of atoms of the chemical element carbon. It is necessary to clearly distinguish between concepts "chemical element" And "simple substance".

For example, diamond and carbon are not the same thing.

Carbon is a chemical element, and diamond is a simple substance formed by the chemical element carbon. In this case, a chemical element (carbon) and a simple substance (diamond) are called differently.

Often a chemical element and a simple substance corresponding to it are called the same. For example, the element oxygen corresponds to a simple substance - oxygen. It is necessary to learn to distinguish where we are talking about an element, and where about a substance! For example, when they say that oxygen is part of water, we are talking about the element oxygen. When they say that oxygen is a gas necessary for breathing, we are talking about a simple substance, oxygen. Simple substances chemical elements subdivided into two groups - metals and non-metals.

Metals and non-metals fundamentally different in their physical properties. All metals at normal conditions solids, with the exception of mercury - the only liquid metal.

Metals are opaque, have a characteristic metallic sheen. Metals are ductile and conduct heat well electricity.Non-metals are not similar to each other in physical properties. So, hydrogen, oxygen, nitrogen are gases, silicon, sulfur, phosphorus are solids. The only liquid non-metal - bromine - is a brown-red liquid. If you draw a conditional line from the chemical element boron to the chemical element astatine, then in the long version

of the Periodic System above the line are non-metallic elements, and below it - metal. In the short version of the Periodic Table, the non-metallic elements are located below this line, and both the metallic and non-metallic elements are above it. This means that it is more convenient to determine whether an element is metallic or non-metallic using the long version of the Periodic System.

This division is conditional, since all elements in one way or another exhibit both metallic and non-metallic properties, but in most cases such a distribution is true.

Compound substances and their classification

If the composition of simple substances includes atoms of only one type, it is easy to guess that the composition of complex substances will include several types of different atoms, at least two. An example of a complex substance is water, you know its chemical formula - H2O.

Water molecules are made up of two types of atoms: hydrogen and oxygen.

Complex Substances Substances that are made up of different types of atoms

Let's do the following experiment. Mix powders of sulfur and zinc. We place the mixture on a metal sheet and set it on fire with a wooden torch. The mixture ignites and quickly burns with a bright flame. After finishing chemical reaction a new substance was formed, which includes sulfur and zinc atoms. The properties of this substance are completely different than the properties of the original substances - sulfur and zinc.

Complex substances are usually divided into two groups: Not organic matter and their derivatives and organic substances and their derivatives. For example, rock salt is an inorganic substance, while the starch found in potatoes is an organic substance.

Structure types of substances

According to the type of particles that make up substances, substances are divided into substances molecular and non-molecular structure. The composition of a substance can include various structural particles, such as atoms, molecules, ions. Therefore, there are three types of substances: substances of atomic, ionic and molecular structure. Substances of different types of structure will have different properties.

Substances of atomic structure

An example of substances atomic structure can be substances formed by the element carbon: graphite and diamond. The composition of these substances includes only carbon atoms, but the properties of these substances are very different. Graphite- fragile, easily exfoliating substance of gray-black color. Diamond- transparent, one of the hardest mineral on the planet. Why do substances composed of the same type of atoms have different properties? It's all about the structure of these substances. The carbon atoms in graphite and diamond bond in different ways. Substances of atomic structure have high boiling and melting points, as a rule, they are insoluble in water, non-volatile. Crystal lattice - an auxiliary geometric image introduced to analyze the structure of a crystal

Substances of molecular structure- These are almost all liquids and most gaseous substances. There are also crystalline substances, the composition of the crystal lattice of which includes molecules. Water is a substance of molecular structure. Ice also has a molecular structure, but unlike liquid water, it has a crystal lattice, where all molecules are strictly ordered. Substances of a molecular structure have low boiling and melting points, are usually brittle, and do not conduct electric current.

Substances of ionic structure

Substances of ionic structure are solid crystalline substances. An example of an ionic compound substance is table salt. Its chemical formula is NaCl. As you can see, NaCl consists of ions Na+ and Cl⎺, alternating in certain places (nodes) of the crystal lattice. Substances of an ionic structure have high melting and boiling points, are brittle, as a rule, are highly soluble in water, and do not conduct electric current. The concepts of "atom", "chemical element" and "simple substance" should not be confused.

• "Atom"- a concrete concept, since atoms really exist.
• "Chemical element" is a collective, abstract concept; in nature, a chemical element exists in the form of free or chemically bound atoms, that is, simple and complex substances.

The names of chemical elements and the corresponding simple substances coincide in most cases. When we talk about the material or component of the mixture - for example, the flask is filled with chlorine gas, water solution bromine, let's take a piece of phosphorus - we are talking about a simple substance. If we say that a chlorine atom contains 17 electrons, a substance contains phosphorus, a molecule consists of two bromine atoms, then we mean a chemical element.

It is necessary to distinguish between the properties (characteristics) of a simple substance (sets of particles) and the properties (characteristics) of a chemical element (an isolated atom of a certain type), see the table below:

Compounds must be distinguished from mixtures, which also consist of different elements. The quantitative ratio of the components of the mixture can be variable, and chemical compounds have a constant composition. For example, in a glass of tea, you can add one spoonful of sugar, or several, and sucrose molecules С12Н22О11 contains exactly 12 carbon atoms, 22 hydrogen atoms and 11 oxygen atoms.

Thus, the composition of compounds can be described by one chemical formula, and the composition mixture is not. The components of the mixture retain their physical and Chemical properties. For example, if you mix iron powder with sulfur, then a mixture of two substances is formed.

Both sulfur and iron in this mixture retain their properties: iron is attracted by a magnet, and sulfur is not wetted by water and floats on its surface. If sulfur and iron react with each other, a new compound is formed with the formula FeS, which does not have the properties of either iron or sulfur, but has a set of its own properties. In conjunction FeS iron and sulfur are bound together and cannot be separated by methods that separate mixtures.

Conclusions from the article on the topic Simple and complex substances

• Simple substances- substances that contain atoms of the same type
• Elements are divided into metals and non-metals
• Compounds are substances that contain different types of atoms.
• Compounds are divided into organic and inorganic
• There are substances of atomic, molecular and ionic structure, their properties are different
• Crystal cell is an auxiliary geometric image introduced to analyze the crystal structure

Chemical compounds and related phases in metal alloys are diverse. Characteristics chemical compounds:

1. The crystal lattice is different from the lattices of the components that form the compound. Atoms are ordered. Chemical compounds have a continuous crystal lattice (Fig. 7).

2. A simple multiple ratio of components is always preserved in the compound, which allows them to be expressed by the formula: A n B m, A and B components; n and m are prime numbers.

3. The properties of a compound rarely differ from the properties of its constituent components. Cu - HB35; Al - HB20; CuAl 2 - HB400.

4. The melting (dissociation) temperature is constant.

5. The formation of a chemical compound is accompanied by a significant thermal effect.

Chemical compounds are formed between components that have a large difference in electronic structure atoms and crystal lattices.

Figure 7. Crystal lattices: a, b - NaCl compound, c - Cu2MnSn compound (the cell consists of 8 copper atoms, 4 manganese atoms and 4 tin atoms)

An example of typical chemical compounds with normal valency are Mg compounds with elements of groups IV-VI of the Periodic system: Mg 2 Sn, Mg 2 Pb, Mg 2 P 2, Mg 2 Sb 2, Mg 3 Bі 2, MgS, etc. Compounds of some metals with others are called intermetallic compounds. chemical bond in intermetallics, it is more often metallic.

Big number chemical compounds formed in metal alloys differ in some features from typical chemical compounds, since it does not obey the laws of valency and does not have a constant composition. Consider the most important chemical compounds formed in alloys.

Implementation phases

Transition metals (Fe, Mn, Cr, Mo, Ti, V, W, etc.) form with non-metals C, N, H compounds: carbides (with WITH), nitrides (with N), borides (with IN), hydrides (with H). These are often referred to as implementation phases.

The implementation phases have the formula:

M 4 X(Fe 4 N, Mn 4 N, etc.),

M 2 X(W 2 C, Mo 2 C, Fe 2 N, Cr 2 N, etc.),

MX(WC, TiC, VC, NbC, TiN, VN, etc.).

The crystal structure of the interstitial phases is determined by the ratio of the atomic radii of the non-metal (Rx) and metal (Rm).

If Rx/Rm< 0,59, то атомы металла в этих фазах расположены по типу одной из простых кристаллических решеток: кубической (К8, К12) и гексагональной (Г12), в которую внедряются атомы неметалла, занимая в ней определенные поры.

Interstitial phases are phases of variable composition, and the corresponding (chemical) formulas usually characterize the maximum content of metals in them.

Interstitial phases have high: electrical conductivity, melting point and high hardness.

Interstitial phases have a crystal lattice different from that of the solvent metal.

On the basis of the implementation phases, it is easy to form subtraction solid solutions(VC, TiC, ZrC, NbC), some atoms are absent at the lattice sites.

Electronic connections.

These compounds form between monovalent (Cu, Ag, Au, Li, Na) metals or metals of transition groups (Mn, Fe, Co, etc.), on the one hand, and with simple metals with a valence of 2 to 5 (Be, Mg , Zn, Cd, Al, etc.) on the other hand.

Compounds of this type (defined by the English metal physicist Hume-Rothery) are characterized by a certain ratio of valence electrons to the number of atoms: 3/2; 21/13; 7/4; each ratio corresponds to a certain crystal lattice.

At a ratio of 3/2, a bcc lattice is formed (denoted? - phase) (CuBe, CuZn, Cu 3 Al, Cu 5 Sn, CoAl, FeAl).

At 21/13 they have a complex cubic lattice (52 atoms per cell) - ? - phase (Cu 5 Zn 8, Cu 31 Sn 8, Cu 9 Al 4, Cu 31 Si 8).

At 7/4 there is a close-packed hexagonal lattice, denoted? - phase (CuZn 3, CuCd 3, Cu 3 Si, Cu 3 Sn, Au 3 Sn, Cu 5 Al 3).

Electronic compounds are found in many technical alloys - Cu and Zn, Cu and Sn (tin), Fe and Al, Cu and Si, etc. Usually, all three phases (?, ?, ?) are observed in the system.

Electronic compounds have a certain ratio of atoms, the crystal lattice differs from the lattices of the components - these are signs of a chemical. connections. However, in compounds there is no ordered arrangement of atoms. With a decrease in temperature (after heating), partial ordering occurs, but not complete. Electronic compounds form with the components that make up solid solutions in a wide range of concentrations.

Thus, this type of compounds should be considered intermediate between chemical compounds and solid solutions.

Table #1 - Electronic Connections

Laves phases

Have a formula AB 2 , are formed when the ratio of the atomic diameters of the components D A /D IN = 1.2 (usually 1.1-1.6). Laves phases have an hcp hexagonal lattice (MgZn 2 and MgNi 2, BaMg 2 , MoBe 2 , TiMn 2) or fcc (MgCu 2 , AgBe 2 , Ca Al 2 , TiBe 2 , TiCr 2). These phases occur as hardening intermetallic phases in superalloys.

• all metals;
• many non-metals (inert gases, C , Si , B , Se , As , Te ).

Molecules are made up of:

• almost all organic substances;
• a small number of inorganic: simple and complex gases ( H2, O2 , O 3, N 2, F2, Cl2, NH3, CO, CO2 , SO 3, SO2, N2O, NO, NO 2, H 2 S), and H2O, Br2, I 2 and some other substances.

Ions are made up of:

• all salts;
• many hydroxides (bases and acids).

Composed of atoms or molecules - of molecules or ions. Molecules of simple substances are made up of the same atoms molecules of complex substances from different atoms.

Law of constancy of composition

The law of constancy of composition was discovered J. Proust in 1801:

Any substance, regardless of the method of its production, has a constant qualitative and quantitative composition.

For example, carbon monoxide CO 2 can be obtained in several ways:

• C + O 2 \u003d t \u003d CO 2
• MgCO 3 + 2HCl \u003d MgCl 2 + H 2 O + CO 2
• 2CO + O 2 \u003d 2CO 2
• CaCO 3 \u003d t \u003d CaO + CO 2

However, regardless of the method of preparation, the molecule CO 2 always has the same compound: 1 carbon atom And 2 oxygen atoms.

Important to remember:

• The opposite assertion is that a certain compound corresponds to a certain composition, wrong. Eg, dimethyl ether And ethanol have the same qualitative and quantitative composition, reflected in the simplest formula C 2 H 6 O, however, they are different substances, as they have a different structure. Their rational formulas in a semi-expanded form will be different:

1. CH 3 - O - CH 3(dimethyl ether);
2. CH 3 - CH 2 - OH(ethanol).

• Law of constancy of composition strictly applicable only to compounds with a molecular structure ( daltonids). Compounds with a non-molecular structure ( berthollids) often have a variable composition.

Chemical composition of complex substances and mechanical mixtures

Compound (chemical compound) is a substance made up of atoms of various chemical substances.

The main features of a chemical compound:

• Uniformity;
• The constancy of the composition;
• Constancy of physical and chemical properties;
• Emission or absorption during formation;
• Impossibility of separation into component parts physical methods.

There are no absolutely pure substances in nature. In any substance there is at least an insignificant percentage of impurities. Therefore, in practice, one always deals with mechanical mixtures of substances. However, if the content of one substance in the mixture significantly exceeds the content of all the others, then conditionally it is believed that such a substance is individual chemical compound.

The permissible content of impurities in substances produced by the industry is determined by standards and depends on the brand of the substance.

The following labeling of substances is generally accepted:

• tech - technical (in its composition it can have up to 20%; impurities);
• h - clean;
• chda – clean for analysis;
• hch - chemically pure;
• osch - high purity (permissible rate of impurities in the composition - up to 10 -6 % ).

Substances that form a mechanical mixture are called components. In this case, substances whose mass makes up a large part of the mass of the mixture are called main components, and all other substances that form the mixture - impurities.

Differences between a mechanical mixture and a chemical compound:

• Any mechanical mixture can be divided into its component parts by physical methods based on the difference densities, boiling points And melting, solubility, magnetizability and others physical properties components that form a mixture (for example, a mixture of wood and iron filings can be separated using H 2 O or magnet)
• Inconstancy of the composition;
• Inconstancy of physical and chemical properties;
• Heterogeneity (although mixtures of gases and liquids can be homogeneous, for example, air).
• During the formation of a mechanical mixture, there is no release and absorption of energy.

An intermediate position between mechanical mixtures and chemical compounds is occupied by solutions:

As for chemical compounds, solutions are characterized by:

• homogeneity;
• the release or absorption of heat during the formation of a solution.

As for mechanical mixtures, solutions are characterized by:

• ease of separation into initial substances by physical methods (for example, by evaporating a solution table salt, available separately H 2 O And NaCl);
• variability of composition - their composition can vary widely.

Chemical composition by mass and by volume

The composition of chemical compounds, as well as the composition of mixtures of various substances and solutions, is expressed in mass fractions (mass%), and the composition of mixtures of liquids and gases, in addition, in volume fractions (volume%).

The composition of a complex substance, expressed in terms of mass fractions of chemical elements, is called composition of matter by mass.

For example, the composition H 2 O by weight:

That is, one can say that chemical composition of water (by mass): 11.11% hydrogen and 88.89% oxygen.

Mass fraction of the component in the mechanical mixture (W)- this is a number showing what part of the mixture is the mass of the component from the total mass of the mixture, taken as a unit or 100%.

W 1 \u003d m 1 / m (see), m (see) \u003d m 1 + m 2 + .... mn,

Where m 1 is the mass of the 1st (arbitrary) component, n is the number of mixture components, m 1 … m n are the masses of the components that form the mixture, m (cm.) is the mass of the mixture.

For example, mass fraction of the main component :

W (main comp) =m (main computer) /m (see)

Mass fraction of impurity:

W (approx.) \u003d m (approx.) / m (see)

The sum of the mass fractions of all components that form the mixture is equal to 1 or 100% .

Volume fraction gas (or liquid) in a mixture of gases (or liquids) is the number , showing what part by volume is the volume of a given gas (or liquid) from the total volume of the mixture, taken as 1 or for 100% .

The composition of a mixture of gases or liquids, expressed in volume fractions, is called composition of the mixture by volume.

For example, composition of the dry air mixture:

• By volume:W about ( N2) = 78.1% , W vol (O2) = 20.9%
• By weight: W(N2) = 75.5%,W(O2) = 23.1%

This example clearly demonstrates that, to avoid confusion, it is always correct to indicate by weight or by volume the content of the mixture component is indicated, because these figures always differ: by mass in the air mixture of oxygen, it turns out 23,1 % , and in terms of volume - total 20,9%.

Solutions can be viewed as mixtures from a solute and a solvent. Therefore, their chemical composition, like the composition of any mixture, can be expressed in mass fractions of components:

W (solv. in-va) \u003d m (dissolve in-va) / m (solution),

Where

m (solution) \u003d m (solvent in-va) + m (solvent)

or

m (p-ra) = p(r-ra) V (r-ra)

Solution composition, expressed in terms of the mass fraction of the solute (in % ), is called percentage concentration this solution.

The composition of solutions of liquids in liquids (for example, alcohol in water, acetone in water) is more conveniently expressed in volume fractions:

W about % (sol. w) \u003d V (sol. w) V (solution) 100%;

Where

V (r-ra) \u003d m (r-ra) / p (r-ra)

or approximately

V (solution) ≈ V (H2O) + V (sol. w)

For example, the alcohol content in wine and vodka products is indicated not in mass, but in volume fractions(% ) and call this number fortress drink.

Compound solutions solids in liquids or gases in liquids are not expressed in volume fractions.

Chemical formula as a display of chemical composition

The qualitative and quantitative composition of a substance is displayed using chemical formula. For example, calcium carbonate has chemical formula « CaCO3 » . The following information can be gleaned from this entry:

• Number of molecules – 1 .
• Amount of substance – 1 mol.
• Qualitative composition(what chemical elements form a substance) - calcium, carbon, oxygen.
• The quantitative composition of the substance:

1. The number of atoms of each element in one molecule of a substance: The calcium carbonate molecule is made up of 1 calcium atom, 1 carbon atom And 3 oxygen atoms .
2. The number of moles of each element in 1 mole of a substance: In 1 mol CaCO 3(6.02 10 23 molecules) contains 1 mol (6.02 10 23 atoms) calcium , 1 mol (6.02 10 23 atoms) carbon And 3 moles (3 6.02 10 23 atoms) of the chemical element oxygen )

• Mass composition of the substance:

1. The mass of each element in 1 mole of a substance: 1 mole of calcium carbonate (100g) contains chemical elements: 40g calcium , 12g carbon, 48g oxygen.
2. Mass fractions of chemical elements in matter (composition of the substance in percent by weight):

W (Ca) \u003d (n (Ca) Ar (Ca)) / Mr (CaCO3) \u003d (1 40) / 100 \u003d 0.4 (40%)

W (C) \u003d (n (Ca) Ar (Ca)) / Mr (CaCO3) \u003d (1 12) / 100 \u003d 0.12 (12%)

W (O) \u003d (n (Ca) Ar (Ca)) / Mr (CaCO3) \u003d (3 16) / 100 \u003d 0.48 (48%)

• For a substance with an ionic structure (salts, acids, bases) - the formula of the substance gives information about number of ions each species in the molecule, their quantity And mass of ions in 1 mol of substance:

1. Molecule CaCO 3 is made up of an ion Ca 2+ and ion CO 3 2-
2. 1 mol ( 6.02 10 23 molecules) CaCO 3 contains 1 mol of Ca 2+ ions And 1 mole of ions CO 3 2- ;
3. 1 mole (100g) of calcium carbonate contains 40g ions Ca 2+ And 60g ions CO 3 2- ;

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For a chemical compound, the following distinctive features are characteristic:

1) The crystal lattice is different from the lattices of the components that form the compound.

2) A simple multiple ratio of its components is always preserved in a compound. This allows us to express their composition by a simple formula A m B n , where A and B are the corresponding elements, n and m are prime numbers.

3) The properties of the compound differ sharply from the properties of its constituent components.

4) The melting (dissociation) temperature is constant.

5) The formation of a chemical compound is accompanied by a significant thermal effect.

Chemical compounds are formed between components that have a large difference in the electronic structure of atoms and crystal lattices.

As an example of typical chemical compounds, one can name such as magnesium compounds with elements of groups IV-VI periodic system: Mg 2 Sn, Mg 2 Pb, Mg 2 P, Mg 3 Sb, MgS and others.

The compounds of some metals with others are common name intermetallic compounds, or intermetallic compounds.

Compounds of a metal with a non-metal (nitrides, oxides, carbides, etc.) can have both metallic and ionic bond. Compounds that have metallic bond are called metallic compounds.

A large number of chemical compounds formed in metal alloys differ from typical chemical compounds, since they do not obey the laws of valency and do not have a constant composition. Consider the most important chemical compounds formed in alloys.

7.2.1 Implementation phases. Transition metals (Fe, Mn, Cr, Mo, etc.) form with carbon, nitrogen, boron and hydrogen, i.e. with elements having a small atomic radius, compounds: carbides, nitrides, borides and hydrides. They have a common structure and properties and are often called penetration phases.

The intercalation phases have the formula M 4 X (Fe 4 N, Mn 4 N, etc.), M 2 X (W 2 C, Fe 2 N, etc.), MX (WC, TiC, TiN, etc.).

The crystal structure of the interstitial phases is determined by the ratio of the atomic radii of the non-metal (R x) and metal (RM). If R x / R M<59, то атомы в этих фазах расположены по типу одной из кристаллических решеток: кубической или гексагональной, в которую внедряются атомы неметалла, занимая в ней определенные поры.

The intercalation phases are phases of variable composition. Carbides and Nitrides have high hardness. The crystal lattice of the interstitial phases differs from that of the metal.

7.2.2. Electronic compounds (Hume-Rothery phases). These compounds are more often formed between monovalent (Cu, Ag, Au, Li, Na) metals or metals of transition groups (Fe, Mn, Co, etc.), on the one hand, and with simple metals with a valence of 2 to 5 (Be,

Mg, Zn, Cd, Al, etc.), on the other hand. Compounds of this type have a certain ratio of the number of valence electrons to the number of atoms, i.e. certain electron concentration. These ratios, as the English metal physicist Hume-Rothery showed, can be 3/2, 21/13 and 7/4, and each ratio corresponds to a certain crystal lattice: a body-centered cubic or hexagonal lattice, a complex cubic lattice and a face-centered cubic lattice, respectively.

7.2.3 Laves phases. These phases have the formula AB 2 and are formed between elements whose atomic diameters are approximately in the ratio 1:1.2. For example, MgZn 2 , TiCr 2 and others. Laves phases occur as hardening intermetallics in heat-resistant alloys.

Solid solutions

Solid solutions are phases in which one of the alloy components retains its crystal lattice, and the atoms of other (or other) components are located in the lattice of the first component (solvent), changing its size. Thus, a solid solution consisting of several components has one type of lattice and represents one phase. In addition, a solid solution does not exist at a certain ratio of components (as in a chemical compound), but in a range of concentrations.

Distinguish between solid solutions .

When solid substitution solutions are formed, the atoms of the dissolved component replace some of the atoms of the solvent in its crystal lattice (Fig. 26, b).

When an interstitial solid solution is formed (Fig. 26, V) the atoms of the dissolved component are located in the interstitials (voids) of the crystal lattice of the solvent.

Fig.26. BCC crystal lattice: A- pure metal b- solid substitution solution, V- solid solution of interstitial; A - base metal atoms, B - substitutional atoms, C - interstitial atoms.

Metals can, to varying degrees, mutually dissolve in each other in the solid state, forming substitutional solid solutions with limited or unlimited solubility. Solid solutions with unlimited solubility are formed under the following conditions:

1) The components must have the same type (isomorphic) crystal lattices.

2) The difference in the atomic sizes of the components should be insignificant and not exceed 10-15%.

3) Components must belong to the same (or related) group of the Periodic Table of Elements.

In some alloys (for example, Cu-Au, Fe-Al), which form substitutional solutions at high temperatures (with random alternation of component atoms), the process of redistribution of atoms occurs during slow cooling or prolonged heating at certain temperatures. Solid solutions that are stable at relatively low temperatures are called orderly solid solutions, or superstructures. Ordered solid solutions can be considered as intermediate phases between solid solutions and chemical compounds. Unlike chemical compounds, the crystal lattice of ordered solid solutions is a solvent lattice. The formation of ordered solid solutions is accompanied by a change in physical and mechanical properties. Strength usually increases and ductility decreases.

The ability to form solid solutions is inherent not only in pure elements, but also in chemical compounds. In these cases, the crystal lattice of the chemical compound is preserved, but an excess number of atoms of one of the components can replace a certain number of atoms of another component. In addition, at the same time, unoccupied places - voids - may appear in individual nodes. Solid solutions based on chemical compounds, the formation of which is accompanied by the appearance of empty spaces at the lattice sites, are called subtraction solutions.

SUMMARY

Under alloy means a substance obtained by fusing two or more elements.

The set of phases that are in equilibrium is called system. phase called homogeneous components of the system, having the same composition, crystal structure and properties, the same state of aggregation and separated from the component parts of the interface. Under structure understand the shape, size and nature of the mutual arrangement of phases in metals and alloys. The components in an alloy can form mechanical mixtures, chemical compounds, or solid solutions.

mechanical mixture two components is formed when they are not capable of mutual dissolution in the solid state and do not enter into a chemical reaction to form a compound.

Chemical compounds are formed between components that have a large difference in the electronic structure of atoms and crystal lattices. The structure and properties of a chemical compound differ from the structure and properties of the components that created it.

The most important chemical compounds formed in alloys are:

Implementation phases

Electronic connections (Hume-Rothery phases)

Laves phases

solid solutions called phases in which one of the components of the alloy retains its crystal lattice, and the atoms of the other (or other) components are located in the lattice of the first component (solvent), changing its size.

Distinguish between solid solutions substitutions, insertions and subtractions.

Review questions

1. What is an alloy?

2. Define the terms "phase", "system", "structure".

3. When is a mechanical mixture of components formed in the alloy, and when is a chemical compound formed?

4. What are solid solutions? What types of solid solutions do you know?

8. STATUS DIAGRAM

state diagram is a graphic representation of the state of the alloy. State diagrams are built for equilibrium conditions or conditions close enough to them. Therefore, a state diagram can also be called an equilibrium diagram.

The equilibrium state corresponds to the minimum value of the free energy. This state can be achieved in the absence of overheating or overcooling of the alloy. The state diagram is a theoretical case, because equilibrium transformations (without supercooling or overheating) in practice cannot

sya. Usually, transformations occurring at low heating or cooling rates are used in practice.

The general laws governing the coexistence of stable phases can be expressed mathematically as phase rules or Gibbs law.

The phase rule gives a quantitative relationship between the degree of freedom of the system and the number of phases of the components.

Under number of degrees of freedom (variance) systems understand the number of external and internal factors (temperature, pressure, concentration), which can be changed without changing the number of phases in the system.

Phase rule.

C \u003d k - f + 2

WITH- number of degrees of freedom, k- number of components, f– number of phases, 2 is the number of external factors.

The phase rule is valid only for the equilibrium state.

The independent variables in the phase rule equation are concentration, temperature, and pressure. If we assume that all transformations in a metal occur at constant pressure, then the number of variables will decrease by one.

C \u003d k - f + 1

Example. Let's see how the degree of freedom of a one-component system changes ( k=1) for the case of pure metal crystallization. When the metal is in a liquid state, i.e. f=1(one phase is a liquid), the number of degrees of freedom is 1. The temperature in this case can change without changing the state of aggregation. At the time of crystallization f=2(two phases - solid and liquid), C=0. This means that the two phases are in equilibrium at a strictly defined temperature (melting point), and it cannot be changed until one phase disappears, i.e. the system will not become monovariant ( C=1).