.

You know that atoms can combine with each other to form both simple and complex substances. In this case, various types of chemical bonds are formed: ionic, covalent (non-polar and polar), metallic and hydrogen. One of the most essential properties of atoms of elements that determine what kind of bond is formed between them - ionic or covalent - This is electronegativity, i.e. the ability of atoms in a compound to attract electrons.

A conditional quantitative assessment of electronegativity is given by the relative electronegativity scale.

In periods, there is a general tendency for the electronegativity of elements to increase, and in groups - for their decrease. Elements are arranged in a series according to their electronegativity, on the basis of which the electronegativity of elements located in different periods can be compared.

The type of chemical bond depends on how large the difference in electronegativity values ​​of the connecting atoms of elements is. The more the atoms of the elements forming the bond differ in electronegativity, the more polar the chemical bond. It is impossible to draw a sharp boundary between the types of chemical bonds. In most compounds, the type of chemical bond is intermediate; for example, a highly polar covalent chemical bond is close to an ionic bond. Depending on which of the limiting cases a chemical bond is closer in nature, it is classified as either an ionic or a covalent polar bond.

Ionic bond.

An ionic bond is formed by the interaction of atoms that differ sharply from each other in electronegativity. For example, the typical metals lithium (Li), sodium (Na), potassium (K), calcium (Ca), strontium (Sr), barium (Ba) form ionic bonds with typical non-metals, mainly halogens.

In addition to alkali metal halides, ionic bonds also form in compounds such as alkalis and salts. For example, in sodium hydroxide (NaOH) and sodium sulfate (Na 2 SO 4) ionic bonds exist only between sodium and oxygen atoms (the remaining bonds are polar covalent).

Covalent nonpolar bond.

When atoms with the same electronegativity interact, molecules with a covalent nonpolar bond are formed. Such a connection exists in the molecules of the following simple substances: H 2, F 2, Cl 2, O 2, N 2. Chemical bonds in these gases are formed through shared electron pairs, i.e. when the corresponding electron clouds overlap, due to the electron-nuclear interaction, which occurs when atoms approach each other.

When composing electronic formulas of substances, it should be remembered that each common electron pair is a conventional image of increased electron density resulting from the overlap of the corresponding electron clouds.

Covalent polar bond.

When atoms interact, the electronegativity values ​​of which differ, but not sharply, the common electron pair shifts to a more electronegative atom. This is the most common type of chemical bond, found in both inorganic and organic compounds.

Covalent bonds also fully include those bonds that are formed by a donor-acceptor mechanism, for example in hydronium and ammonium ions.

Metal connection.

The bond that is formed as a result of the interaction of relatively free electrons with metal ions is called a metallic bond. This type of bond is characteristic of simple substances - metals.

The essence of the process of metal bond formation is as follows: metal atoms easily give up valence electrons and turn into positively charged ions. Relatively free electrons, detached from the atom, move between positive metal ions. A metallic bond arises between them, i.e. Electrons, as it were, cement the positive ions of the crystal lattice of metals.

Hydrogen bond.

A bond that forms between the hydrogen atoms of one molecule and an atom of a strongly electronegative element(O,N,F) another molecule is called a hydrogen bond.

The question may arise: why does hydrogen form such a specific chemical bond?

This is explained by the fact that the atomic radius of hydrogen is very small. In addition, when displacing or completely donating its only electron, hydrogen acquires a relatively high positive charge, due to which the hydrogen of one molecule interacts with atoms of electronegative elements that have a partial negative charge that goes into the composition of other molecules (HF, H 2 O, NH 3) .

Let's look at some examples. We usually represent the composition of water with the chemical formula H 2 O. However, this is not entirely accurate. It would be more correct to denote the composition of water by the formula (H 2 O)n, where n = 2,3,4, etc. This is explained by the fact that individual water molecules are connected to each other through hydrogen bonds.

Hydrogen bonds are usually denoted by dots. It is much weaker than ionic or covalent bonds, but stronger than ordinary intermolecular interactions.

The presence of hydrogen bonds explains the increase in water volume with decreasing temperature. This is due to the fact that as the temperature decreases, the molecules become stronger and therefore the density of their “packing” decreases.

When studying organic chemistry, the following question arose: why are the boiling points of alcohols much higher than the corresponding hydrocarbons? This is explained by the fact that hydrogen bonds also form between alcohol molecules.

An increase in the boiling point of alcohols also occurs due to the enlargement of their molecules.

Hydrogen bonding is also characteristic of many other organic compounds (phenols, carboxylic acids, etc.). From courses in organic chemistry and general biology, you know that the presence of a hydrogen bond explains the secondary structure of proteins, the structure of the double helix of DNA, i.e. the phenomenon of complementarity.

First of all, let's consider the structure of the ammonia molecule NH 3. As you already know, at the outer energy level, nitrogen atoms contain five electrons, of which three electrons are unpaired. It is they who participate in the formation of three covalent bonds with three hydrogen atoms during the formation of the ammonia molecule NH 3.

Three common electron pairs are shifted towards the more electronegative nitrogen atom, and since the ammonia molecule has the shape of a triangular pyramid (Fig. 128), as a result of the displacement of electron pairs, a dipole appears, i.e. a molecule with two poles.

Rice. 128.
The structure of the ammonia molecule

Ammonia molecules (in liquid ammonia) interact by bonding with each other:

This special type of chemical intermolecular bond, as you already know, is called a hydrogen bond.

Ammonia is a colorless gas with a pungent odor, almost twice as light as air. Ammonia should not be inhaled for long periods of time as it is poisonous. This gas easily liquefies at normal pressure and a temperature of -33.4 °C. When liquid ammonia evaporates from the environment, a lot of heat is absorbed, which is why ammonia is used in refrigeration units.

Ammonia is highly soluble in water: at 20 °C, about 710 volumes of ammonia dissolve in 1 volume of water (Fig. 129). A concentrated (25% by weight) aqueous solution of ammonia is called aqueous ammonia or ammonia water, and a 10% ammonia solution used in medicine is known as ammonia. In an aqueous solution of ammonia, a weak compound is formed - ammonia hydrate NH 3 H 2 O.

Rice. 129.
“Ammonia fountain” (dissolving ammonia in water)

If you add a few drops of phenolphthalein to an ammonia solution, the solution will turn crimson, indicating an alkaline environment. The alkaline reaction of aqueous solutions of ammonia is explained by the presence of hydroxide ions OH -:

If an ammonia solution colored with phenolphthalein is heated, the color will disappear (why?).

Laboratory experiment No. 30
Studying the properties of ammonia

Ammonia reacts with acids to form ammonium salts. This interaction can be observed in the following experiment: bring a glass rod or glass moistened with an ammonia solution to another rod or glass moistened with hydrochloric acid - thick white smoke will appear (Fig. 130):

Rice. 130.
"Smoke without fire"

So believe after this saying that there is no smoke without fire.

Both an aqueous solution of ammonia and ammonium salts contain a special ion - ammonium cation NH + 4, which plays the role of a metal cation. The ammonium ion is formed as a result of the formation of a covalent bond between a nitrogen atom having a free (lone) electron pair and a hydrogen cation, which passes to ammonia from acid or water molecules:

When an ammonium ion is formed, the donor of a free electron pair is the nitrogen atom in ammonia, and the acceptor is the hydrogen cation of an acid or water.

You can predict another chemical property of ammonia yourself if you pay attention to the oxidation state of nitrogen atoms in it, namely -3. Of course, ammonia is the strongest reducing agent, that is, its nitrogen atoms can only give up electrons, but not accept them. Thus, ammonia can be oxidized either to free nitrogen (without the participation of a catalyst):

4NH 3 + 3O 2 = 2N 2 + 6H 2 O,

or to nitrogen oxide (II) (in the presence of a catalyst):

In industry, ammonia is produced by synthesis from nitrogen and hydrogen (Fig. 131).

Rice. 131.
Industrial installation (a) and scheme for industrial production of ammonia (b)

In the laboratory, ammonia is obtained by the action of slaked lime Ca(OH) 2 on ammonium salts, most often ammonium chloride:

The gas is collected in a vessel turned upside down, and is recognized either by smell, or by the blueness of wet red litmus paper, or by the appearance of white smoke when a stick moistened with hydrochloric acid is introduced.

Ammonia and its salts are widely used in industry and technology, agriculture, and everyday life. Their main areas of application are shown in Figure 132.

Rice. 132.
Application of ammonia and ammonium salts:
1.2 - in refrigeration units; 3 - production of mineral fertilizers; 4 - production of nitric acid; 5 - for soldering; 6 - production of explosives; 7 - in medicine and in everyday life (ammonia)

New words and concepts

1. The structure of the ammonia molecule.
2. Hydrogen bond.
3. Properties of ammonia: interaction with water, acids and oxygen.
4. Donor-acceptor mechanism for the formation of ammonium ion.
5. Receiving, collecting and recognizing ammonia.

DEFINITION

Ammonia- hydrogen nitride.

Formula – NH 3. Molar mass – 17 g/mol.

Physical properties of ammonia

Ammonia (NH 3) is a colorless gas with a pungent odor (the smell of “ammonia”), lighter than air, highly soluble in water (one volume of water will dissolve up to 700 volumes of ammonia). The concentrated ammonia solution contains 25% (mass) ammonia and has a density of 0.91 g/cm 3 .

The bonds between atoms in the ammonia molecule are covalent. General view of the AB 3 molecule. All valence orbitals of the nitrogen atom enter into hybridization, therefore, the type of hybridization of the ammonia molecule is sp 3. Ammonia has a geometric structure of the AB 3 E type - a trigonal pyramid (Fig. 1).

Rice. 1. The structure of the ammonia molecule.

Chemical properties of ammonia

Chemically, ammonia is quite active: it reacts with many substances. The oxidation degree of nitrogen in ammonia “-3” is minimal, so ammonia exhibits only reducing properties.

When ammonia is heated with halogens, heavy metal oxides and oxygen, nitrogen is formed:

2NH 3 + 3Br 2 = N 2 + 6HBr

2NH 3 + 3CuO = 3Cu + N 2 + 3H 2 O

4NH 3 +3O 2 = 2N 2 + 6H 2 O

In the presence of a catalyst, ammonia can be oxidized to nitrogen oxide (II):

4NH 3 + 5O 2 = 4NO + 6H 2 O (catalyst - platinum)

Unlike hydrogen compounds of non-metals of groups VI and VII, ammonia does not exhibit acidic properties. However, hydrogen atoms in its molecule are still capable of being replaced by metal atoms. When hydrogen is completely replaced by a metal, compounds called nitrides are formed, which can also be obtained by direct interaction of nitrogen with the metal at high temperatures.

The main properties of ammonia are due to the presence of a lone pair of electrons on the nitrogen atom. A solution of ammonia in water is alkaline:

NH 3 + H 2 O ↔ NH 4 OH ↔ NH 4 + + OH —

When ammonia interacts with acids, ammonium salts are formed, which decompose when heated:

NH 3 + HCl = NH 4 Cl

NH 4 Cl = NH 3 + HCl (when heated)

Ammonia production

There are industrial and laboratory methods for producing ammonia. In the laboratory, ammonia is obtained by the action of alkalis on solutions of ammonium salts when heated:

NH 4 Cl + KOH = NH 3 + KCl + H 2 O

NH 4 + + OH - = NH 3 + H 2 O

This reaction is qualitative for ammonium ions.

Application of ammonia

Ammonia production is one of the most important technological processes worldwide. About 100 million tons of ammonia are produced annually in the world. Ammonia is released in liquid form or in the form of a 25% aqueous solution - ammonia water. The main areas of use of ammonia are the production of nitric acid (subsequent production of nitrogen-containing mineral fertilizers), ammonium salts, urea, hexamine, synthetic fibers (nylon and nylon). Ammonia is used as a refrigerant in industrial refrigeration units and as a bleaching agent in the cleaning and dyeing of cotton, wool and silk.

Examples of problem solving

EXAMPLE 1

Exercise	What is the mass and volume of ammonia that will be required to produce 5 tons of ammonium nitrate?
Solution	Let us write the equation for the reaction of producing ammonium nitrate from ammonia and nitric acid: NH 3 + HNO 3 = NH 4 NO 3 According to the reaction equation, the amount of ammonium nitrate substance is equal to 1 mol - v(NH 4 NO 3) = 1 mol. Then, the mass of ammonium nitrate calculated from the reaction equation: m(NH 4 NO 3) = v(NH 4 NO 3) × M(NH 4 NO 3); m(NH 4 NO 3) = 1×80 = 80 t According to the reaction equation, the amount of ammonia substance is also equal to 1 mol - v(NH 3) = 1 mol. Then, the mass of ammonia calculated by the equation: m(NH 3) = v(NH 3)×M(NH 3); m(NH 3) = 1×17 = 17 t Let's make a proportion and find the mass of ammonia (practical): x g NH 3 – 5 t NH 4 NO 3 17 t NH 3 – 80 t NH 4 NO 3 x = 17×5/80 = 1.06 m(NH 3) = 1.06 t Let’s make a similar proportion to find the volume of ammonia: 1.06 g NH 3 – x l NH 3 17 t NH 3 – 22.4×10 3 m 3 NH 3 x = 22.4×10 3 ×1.06 /17 = 1.4×10 3 V(NH 3) = 1.4 × 10 3 m 3
Answer	Ammonia mass - 1.06 t, ammonia volume - 1.4×10 m

E.N.Frenkel

Chemistry tutorial

A manual for those who do not know, but want to learn and understand chemistry

Part I. Elements of general chemistry
(first difficulty level)

Continuation. See in No. 13, 18, 23/2007;
6/2008

Chapter 4. The concept of chemical bonding

Previous chapters of this manual discussed the fact that matter is made up of molecules, and molecules are made up of atoms. Have you ever wondered: why don’t the atoms that make up a molecule fly apart in different directions? What holds the atoms in a molecule?

Holds them back chemical bond .

In order to understand the nature of a chemical bond, it is enough to recall a simple physical experiment. Two balls hanging side by side on strings do not “react” to each other in any way. But if you give one ball a positive charge and the other a negative charge, they will attract each other. Isn't this the force that attracts atoms to each other? Indeed, research has shown that chemical bond is electrical in nature.

Where do the charges in neutral atoms come from?

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When describing the structure of atoms, it was shown that all atoms, with the exception of the noble gas atoms, tend to gain or give up electrons. The reason is the formation of a stable eight-electron outer level (like noble gases). When receiving or giving away electrons, electric charges arise and, as a result, electrostatic interaction between particles. This is how it arises ionic bond , i.e. bond between ions.

Ions are stable charged particles that are formed as a result of accepting or losing electrons.

For example, an atom of an active metal and an active nonmetal participates in a reaction:

In this process, a metal atom (sodium) gives up electrons:

a) Is such a particle stable?

b) How many electrons are left in the sodium atom?

c) Will this particle have a charge?

Thus, in this process a stable particle was formed (8 electrons at the outer level), which has a charge, because the nucleus of the sodium atom still has a charge of +11, and the remaining electrons have a total charge of –10. Therefore, the charge of the sodium ion is +1. A brief recording of this process looks like this:

What happens to the sulfur atom? This atom accepts electrons until the outer level is completed:

A simple calculation shows that this particle has a charge:

Oppositely charged ions attract each other, resulting in an ionic bond and an “ionic molecule”:

There are other ways to form ions, which will be discussed in Chapter 6.

Formally, sodium sulfide is credited with exactly this molecular composition, although the substance, consisting of ions, has approximately the following structure (Fig. 1):

Thus, substances consisting of ions do not contain individual molecules! In this case, we can only talk about a conditional “ionic molecule”.

Task 4.1. Show how the transfer of electrons occurs when an ionic bond occurs between atoms:

a) calcium and chlorine;

b) aluminum and oxygen.

REMEMBER! A metal atom gives up outer electrons; The nonmetal atom takes on the missing electrons.

Conclusion. According to the mechanism described above, an ionic bond is formed between atoms of active metals and active nonmetals.

Research, however, shows that the complete transfer of electrons from one atom to another does not always occur. Very often, a chemical bond is formed not by giving and receiving electrons, but as a result of the formation of common electron pairs*. This connection is called covalent .

A covalent bond occurs due to the formation of shared electron pairs. This type of bond is formed, for example, between non-metal atoms. Thus, it is known that the nitrogen molecule consists of two atoms - N 2. How does a covalent bond arise between these atoms? To answer this question, it is necessary to consider the structure of the nitrogen atom:

Question. How many electrons are missing before completing the outer level?

ANSWER: Three electrons are missing. Therefore, denoting each electron of the outer level with a dot, we obtain:

Question. Why are three electrons represented by single dots?

ANSWER: The point is that we want to show the formation of shared pairs of electrons. A pair is two electrons. Such a pair occurs, in particular, if each atom provides one electron to form a pair. The nitrogen atom is three electrons short of completing the outer level. This means that he must “prepare” three single electrons to form future pairs (Fig. 2).

Received electron formula of molecule nitrogen, which shows that each nitrogen atom now has eight electrons (six of them are circled in an oval plus 2 electrons of their own); three common pairs of electrons appeared between the atoms (the intersection of the circles).

Each pair of electrons corresponds to one covalent bond. How many covalent bonds were formed? Three. We show each bond (each shared pair of electrons) using a dash (valence stroke):

All these formulas do not, however, give an answer to the question: what connects atoms when a covalent bond is formed? The electronic formula shows that a common pair of electrons is located between the atoms. An excess negative charge appears in this region of space. And the nuclei of atoms, as is known, have a positive charge. Thus, the nuclei of both atoms are attracted to a common negative charge, which arose due to common electron pairs (more precisely, the intersection of electron clouds) (Fig. 3).

Can such a bond arise between different atoms? Maybe. Let a nitrogen atom interact with hydrogen atoms:

The structure of the hydrogen atom shows that the atom has one electron. How many of these atoms must be taken so that the nitrogen atom “gets what it wants” - three electrons? Obviously three hydrogen atoms
(Fig. 4):

Cross in Fig. 4 indicates the electrons of the hydrogen atom. The electronic formula of the ammonia molecule shows that the nitrogen atom now has eight electrons, and each hydrogen atom now has two electrons (and there cannot be more at the first energy level).

The graphical formula shows that the nitrogen atom has valency three (three dashes, or three valence strokes), and each hydrogen atom has valency one (one dash).

Although both N 2 and NH 3 molecules contain the same nitrogen atom, the chemical bonds between the atoms are different from each other. In the nitrogen molecule N2, chemical bonds form identical atoms, so the shared pairs of electrons are located in the middle between the atoms. The atoms remain neutral. This chemical bond is called non-polar .

In the ammonia molecule NH 3 a chemical bond is formed different atoms. Therefore, one of the atoms (in this case, the nitrogen atom) attracts the common pair of electrons more strongly. The common pairs of electrons are shifted towards the nitrogen atom, and a small negative charge appears on it, and a positive one on the hydrogen atom, poles of electricity have arisen - a bond polar (Fig. 5).

Most substances built using covalent bonds consist of individual molecules (Fig. 6).

From Fig. Figure 6 shows that there are chemical bonds between atoms, but between molecules they are absent or insignificant.

The type of chemical bond affects the properties of a substance and its behavior in solutions. So, the greater the attraction between particles, the more difficult it is to tear them away from each other and the more difficult it is to convert a solid into a gaseous or liquid state. Try to determine in the diagram below which particles have greater interaction forces and what chemical bond is formed (Fig. 7).

If you carefully read the chapter, your answer will be as follows: the maximum interaction between particles occurs in case I (ionic bond). Therefore, all such substances are solid. The least interaction between uncharged particles (case III - non-polar covalent bond). Such substances are most often gases.

Task 4.2. Determine what chemical bond occurs between atoms in the substances: NaCl, HCl, Cl 2, AlCl 3, H 2 O. Give explanations.

Task 4.3. Make electronic and graphic formulas for those substances from task 4.2 in which you determined the presence of a covalent bond. For ionic bonding, draw electron transfer diagrams.

Chapter 5. Solutions

There is no person on Earth who has not seen solutions. What is this?

A solution is a homogeneous mixture of two or more components (components or substances).

What is a homogeneous mixture? The homogeneity of a mixture assumes that between its constituent substances missing interface. In this case, it is impossible, at least visually, to determine how many substances formed a given mixture. For example, looking at tap water in a glass, it is difficult to imagine that, in addition to water molecules, it contains a good dozen ions and molecules (O 2, CO 2, Ca 2+, etc.). And no microscope will help you see these particles.

But the absence of an interface is not the only sign of homogeneity. In a homogeneous mixture the composition of the mixture is the same at any point. Therefore, to obtain a solution, you need to thoroughly mix the components (substances) that form it.

Solutions can have different states of aggregation:

Gaseous solutions (for example, air - a mixture of gases O 2, N 2, CO 2, Ar);

Liquid solutions (for example, cologne, syrup, brine);

Solid solutions (for example, alloys).

One of the substances that forms a solution is called solvent. The solvent has the same state of aggregation as the solution. So, for liquid solutions it is a liquid: water, oil, gasoline, etc. Most often in practice, aqueous solutions are used. They will be discussed further (unless a corresponding reservation is made).

What happens when various substances dissolve in water? Why do some substances dissolve well in water, while others dissolve poorly? What determines solubility - the ability of a substance to dissolve in water?

Let's imagine that a piece of sugar is placed in a glass of warm water. It lay there, shrank in size and... disappeared. Where? Is the law of conservation of matter (its mass, energy) being violated? No. Take a sip of the resulting solution and you will be convinced that the water is sweet and the sugar has not disappeared. But why is it not visible?

The fact is that during dissolution, crushing (grinding) of the substance occurs. In this case, a piece of sugar has broken down into molecules, but we cannot see them. Yes, but why doesn’t the sugar lying on the table break down into molecules? Why does a piece of margarine dipped into water also not disappear? But because the fragmentation of the soluble substance occurs under the influence of a solvent, for example water. But the solvent will be able to “pull” the crystal, the solid substance, into molecules if it manages to “catch on” to these particles. In other words, when a substance dissolves there must be interaction between substance and solvent.

When is such interaction possible? Only in the case when the structure of the substances (both the soluble and the solvent) is similar. The rule of alchemists has long been known: “like dissolves in like.” In our examples, the sugar molecules are polar and there are certain interaction forces between them and the polar water molecules. There are no such forces between non-polar fat molecules and polar water molecules. Therefore, fats do not dissolve in water. Thus, solubility depends on the nature of the solute and solvent.

As a result of the interaction between the solute and water, compounds are formed - hydrates. These can be very strong connections:

Such compounds exist as individual substances: bases, oxygen-containing acids. Naturally, during the formation of these compounds, strong chemical bonds arise and heat is released. So, when CaO (quicklime) is dissolved in water, so much heat is released that the mixture boils.

But why, when sugar or salt is dissolved in water, the resulting solution does not heat up? Firstly, not all hydrates are as strong as sulfuric acid or calcium hydroxide. There are hydrates of salts (crystal hydrates), which easily decompose when heated:

Secondly, during dissolution, as already mentioned, a crushing process occurs. And this consumes energy and absorbs heat.

Since both processes occur simultaneously, the solution can heat up or cool down, depending on which process predominates.

Task 5.1. Determine which process - crushing or hydration - predominates in each case:

a) when dissolving sulfuric acid in water, if the solution is heated;

b) when ammonium nitrate is dissolved in water, if the solution has cooled;

c) when table salt is dissolved in water, if the temperature of the solution remains virtually unchanged.

Since the temperature of the solution changes during dissolution, it is natural to assume that solubility depends on temperature. Indeed, the solubility of most solids increases with heating. The solubility of gases decreases when heated. Therefore, solids are usually dissolved in warm or hot water, while carbonated drinks are kept cold.

Solubility(ability to dissolve) substances does not depend on the grinding of the substance or the intensity of mixing. But by increasing the temperature, grinding the substance, stirring the finished solution, you can speed up the dissolution process. By changing the conditions for obtaining the solution, it is possible to obtain solutions of different compositions. Naturally, there is a limit, upon reaching which it is easy to discover that the substance is no longer soluble in water. This solution is called rich. For highly soluble substances, a saturated solution will contain a lot of solute. Thus, a saturated solution of KNO 3 at 100 °C contains 245 g of salt per 100 g of water (in 345 g of solution), this concentrated solution. Saturated solutions of poorly soluble substances contain negligible masses of dissolved compounds. Thus, a saturated solution of silver chloride contains 0.15 mg of AgCl in 100 g of water. This is very diluted solution.

Thus, if a solution contains a lot of solute relative to the solvent, it is called concentrated, if there is little substance, it is called dilute. Very often, its properties, and therefore its application, depend on the composition of the solution.

Thus, a diluted solution of acetic acid (table vinegar) is used as a flavoring, and a concentrated solution of this acid (acetic essence when taken orally) can cause a fatal burn.

In order to reflect the quantitative composition of solutions, use a value called mass fraction of solute :

Where m(v-va) – mass of solute in solution; m(solution) – the total mass of a solution containing a solute and a solvent.

So, if 100 g of vinegar contains 6 g of acetic acid, then we are talking about a 6% solution of acetic acid (this is table vinegar). Methods for solving problems using the concept of solute mass fraction will be discussed in Chapter 8.

Conclusions for Chapter 5. Solutions are homogeneous mixtures consisting of at least two substances, one of which is called a solvent, the other is a solute. When dissolved, this substance interacts with the solvent, due to which the solute is crushed. The composition of a solution is expressed using the mass fraction of solute in the solution.

* These electron pairs occur at the intersection of electron clouds.

To be continued

Help me solve chemistry please. Indicate the type of bond in the molecules NH3, CaCl2, Al2O3, BaS... and received the best answer

Answer from Olga Lyabina[guru]
1) NH3 bond type cov. polar. Three unpaired electrons of nitrogen and one of hydrogen each take part in the formation of a bond. There are no pi bonds. sp3 hybridization. The shape of the molecule is pyramidal (one orbital does not participate in hybridization, the tetrahedron turns into a pyramid)
CaCl2 type of bond is ionic. The bond formation involves two calcium electrons in the s orbital, which accept two chlorine atoms, completing their third level. no pi bonds, hybridization type sp. they are located in space at an angle of 180 degrees
Al2O3 bond type is ionic. Three electrons from the s and p orbitals of aluminum are involved in the formation of the bond, which oxygen accepts, completing its second level. O=Al-O-Al=O. There are pi bonds between oxygen and aluminum. sp hybridization type most likely.
BaS bond type is ionic. two electrons of barium are accepted by sulfur. Ba=S is one pi bond. hybridization sp. Flat molecule.
2) AgNO3
silver is reduced at the cathode
K Ag+ + e = Ag
water oxidizes at the anode
A 2H2O - 4e = O2 + 4H+
according to Faraday's law (whatever...) the mass (volume) of the substance released at the cathode is proportional to the amount of electricity passing through the solution
m(Ag) = Me/zF *I*t = 32.23 g
V(O2) = Ve/F *I*t = 1.67 l

Reply from 2 answers[guru]

Hello! Here is a selection of topics with answers to your question: Help me solve chemistry, please. Indicate the type of bond in the molecules NH3, CaCl2, Al2O3, BaS...