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Water is a very reactive substance due to the presence of two lone pairs of electrons in its molecule.

Chemical reactions involving water can be divided into 3 groups:

1. Reactions in which water exhibits oxidizing properties.

2. Reactions in which water is a reducing agent.

3. Exchange and addition reactions.

1. At room temperature, water oxidizes alkali and alkaline earth metals (except magnesium):

Hydrides of alkali and alkaline earth metals are oxidized similarly with water:

Magnesium and zinc in the form of dust are oxidized by water at. Less active substances interact with only at fairly high temperatures

2. Water is oxidized by atomic oxygen and fluorine at ordinary temperature

In this reaction, they are formed due to the interaction of oxygen atoms both with each other and with and.

When chlorine interacts with water, a reaction occurs with the formation of hypochlorous and hydrochloric acids

Reactions proceed similarly when bromine and iodine are dissolved in water, with the only difference being that the equilibrium is strongly shifted (especially for) from right to left.

It should also be borne in mind that chlorine at temperatures above 100° or in the cold when exposed to light, and bromine at 550° and above oxidize water, releasing oxygen

3. Many substances (salts, acid halides, etc.) enter into exchange and addition reactions with water:

When salts, acids, bases and other substances are dissolved in water, they undergo hydration, i.e., the addition of water molecules to a molecule of the dissolved substance.

The catalytic effect of water is of great importance. Many reactions occur only in the presence of traces of water and do not proceed at all without it. So, for example, chlorine in the complete absence of moisture does not affect iron; an explosive mixture without traces of moisture does not explode; when dry, it does not react.

In some cases, water is a catalytic poison, for example, for iron in the synthesis of ammonia.

First of all, remember that metals are generally divided into three groups:

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

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

3) Low-active metals: metals located in the activity series to the right of hydrogen.

First of all, you need to remember that low-active metals (i.e. 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 temperatures and in the cold), and the reaction is accompanied by the release of hydrogen and the formation of metal hydroxide. For example:

2Na + 2H 2 O = 2NaOH + H 2

Ca + 2H 2 O = Ca(OH) 2 + H 2

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

Mg + 2H 2 O = 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 is required:

2Al + 6H 2 O = 2Al(OH) 3 + 3H 2

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

WATER

A water molecule consists of an oxygen atom and two hydrogen atoms attached to it at an angle of 104.5°.

Physical properties

WATER, ICE AND STEAM,respectively, liquid, solid and gaseous states of a chemical compound with the molecular formula H 2 O.

Due to the strong attraction between molecules, water has high melting points (0C) and boiling points (100C). A thick layer of water has a blue color, which is determined not only by its physical properties, but also by the presence of suspended particles of impurities. The water of mountain rivers is greenish due to the suspended particles of calcium carbonate it contains. Pure water is a poor conductor of electricity. The density of water is maximum at 4C; it is equal to 1 g/cm3. Ice has a lower density than liquid water and floats to its surface, which is very important for the inhabitants of reservoirs in winter.

Water has an exceptionally high heat capacity, so it heats up slowly and cools down slowly. Thanks to this, water pools regulate the temperature on our planet.

Chemical properties of water

Water is a highly reactive substance. Under normal conditions, it reacts with many basic and acidic oxides, as well as with alkali and alkaline earth metals. Water forms numerous compounds - crystalline hydrates.

Under the influence of electric current, water decomposes into hydrogen and oxygen:

2H2O electricity= 2 H 2 + O 2

Video "Electrolysis of water"

Mg + 2H 2 O = Mg(OH) 2 + H 2

• Beryllium with water forms an amphoteric oxide: Be + H 2 O = BeO + H 2

1. Active metals are:

Li, Na, K, Rb, Cs, Fr– 1 group “A”

Ca, Sr, Ba, Ra– 2nd group “A”

2. Metal activity series

3. Alkali is a water-soluble base, a complex substance which includes an active metal and a hydroxyl group OH ( I).

4. Medium activity metals in the voltage range range from MgbeforePb(aluminum in special position)

Video "Interaction of sodium with water"

Remember!!!

Aluminum reacts with water like active metals to form a base:

2Al + 6H 2 O = 2Al( OH) 3 + 3H 2

Using the sample, write down the interaction reaction equations:

WITHO2 + H2O =

SO 3 + H 2 O =

Cl 2 O 7 + H 2 O =

P 2 O 5 + H 2 O (hot) =

N 2 O 5 + H 2 O =

11.1. Physical dissolution

If any substance gets into water, it may:
a) dissolve in water, that is, mix with it at the atomic-molecular level;
b) enter into a chemical reaction with water;
c) do not dissolve or react.
What determines the result of the interaction of a substance with water? Naturally, it depends on the characteristics of the substance and the characteristics of water.
Let's start with dissolution and consider which characteristics of water and substances interacting with it are most important in these processes.
Place a small portion of naphthalene C 10 H 8 into two test tubes. Pour water into one of the test tubes and heptane C 7 H 16 into the other (you can use gasoline instead of pure heptane). Naphthalene will dissolve in heptane, but not in water. Let's check whether naphthalene really dissolved in heptane or reacted with it. To do this, place a few drops of the solution on the glass and wait until the heptane evaporates - colorless lamellar crystals form on the glass. You can tell that it is naphthalene by its characteristic smell.

One of the differences between heptane and water is that its molecules are non-polar, while water molecules are polar. In addition, there are hydrogen bonds between water molecules, but there are none between heptane molecules.

To dissolve naphthalene in heptane, it is necessary to break the weak intermolecular bonds between naphthalene molecules and the weak intermolecular bonds between heptane molecules. When dissolved, equally weak intermolecular bonds are formed between naphthalene and heptane molecules. The thermal effect of such a process is practically zero.
Why does naphthalene dissolve in heptane? Only due to the entropy factor (disorder in the naphthalene-heptane system increases).

To dissolve naphthalene in water, it is necessary, in addition to weak bonds between its molecules, to break hydrogen bonds between water molecules. In this case, hydrogen bonds between naphthalene and water molecules are not formed. The process turns out to be endothermic and so energetically unfavorable that the entropy factor cannot help here.
But if instead of naphthalene we take another substance whose molecules are capable of forming hydrogen bonds with water molecules, will such a substance dissolve in water?
If there are no other obstacles, then it will be. For example, you know that sugar (sucrose C 12 H 22 O 11) is perfectly soluble in water. Looking at the structural formula of sucrose, you will see that its molecule contains –O–H groups that can form hydrogen bonds with water molecules.
Make sure experimentally that sucrose is slightly soluble in heptane, and try to explain on your own why the properties of naphthalene and sucrose are so different.
The dissolution of naphthalene in heptane and sucrose in water is called physical dissolution.

Only molecular substances can physically dissolve.

The other components of the solution are called dissolved substances.

The patterns we have identified also apply to cases of dissolution of liquid and gaseous substances in water (and in most other solvents). If all the substances forming a solution were in the same state of aggregation before dissolution, then the solvent is usually called the substance that is more abundant in the solution. The exception to this rule is water: it is usually called a solvent even if there is less of it than the solute.
The reason for the physical dissolution of a substance in water can be not only the formation of hydrogen bonds between the molecules of the solute and water, but also the formation of other types of intermolecular bonds. This happens primarily in the case of dissolving gaseous substances (for example, carbon dioxide or chlorine) in water, in which the molecules are not connected to each other at all, as well as some liquids with very weak intermolecular bonds (for example, bromine). The gain in energy is achieved here due to the orientation of dipoles (water molecules) around polar molecules or polar bonds in the soluble substance, and in the case of chlorine or bromine, it is caused by the tendency to attach electrons of chlorine and bromine atoms, which is also preserved in the molecules of these simple substances (more details - in § 11.4).
In all these cases, substances are much less soluble in water than when hydrogen bonds are formed.
If you remove the solvent from the solution (for example, as you did in the case of a solution of naphthalene in heptane), then the dissolved substance will be released in a chemically unchanged form.

PHYSICAL DISSOLUTION, SOLVENT.
1.Explain why heptane is insoluble in water
2. Tell me the sign of the thermal effect of dissolving ethyl alcohol (ethanol) in water.
3. Why is ammonia highly soluble in water, but oxygen is poorly soluble?
4.Which substance is more soluble in water – ammonia or phosphine (PH 3)?
5.Explain the reason for the better solubility of ozone in water than oxygen.
6. Determine the mass fraction of glucose (grape sugar, C 6 H 12 O 6) in an aqueous solution if 120 ml of water and 30 g of glucose were used for its preparation (take the density of water equal to 1 g/ml). What is the concentration of glucose in this solution if the density of the solution is 1.15 g/ml?
7. How much sugar (sucrose) can be isolated from 250 g of syrup with a mass fraction of water equal to 35%?

1. Experiments on dissolving various substances in various solvents.
2. Preparation of solutions.

In the first paragraph, we examined cases of dissolution of substances in which the chemical bonds remained unchanged. But this is not always the case.
Place some sodium chloride crystals in a test tube and add water. After some time, the crystals will dissolve. What happened?
Sodium chloride is a non-molecular substance. A NaCl crystal consists of Na and Cl ions. When such a crystal gets into water, these ions pass into it. In this case, ionic bonds in the crystal and hydrogen bonds between water molecules are broken. The ions that enter the water interact with water molecules. In the case of chloride ions, this interaction is limited by the electrostatic attraction of dipole water molecules to the anion, and in the case of sodium cations it approaches donor-acceptor in nature. One way or another, the ions are covered hydration shell(Fig. 11.1).

In the form of a reaction equation, this can be written as follows:

NaCl cr + ( n + m)H 2 O = + A

or for short , where index aq means that the ion hydrated. This equation is called ionic equation.

You can also write down the “molecular” equation of this process: (this name has been preserved since the time when it was assumed that all substances consist of molecules)

Hydrated ions are less attracted to each other, and the energy of thermal motion is sufficient to prevent these ions from sticking together into a crystal.

In practice, the presence of ions in a solution can be easily confirmed by studying the electrical conductivity of sodium chloride, water and the resulting solution. You already know that sodium chloride crystals do not conduct electric current, because although they contain charged particles - ions, they are “fixed” in the crystal and cannot move. Water conducts electricity very poorly, because although oxonium and hydroxide ions are formed in it due to autoprotolysis, there are very few of them few. A sodium chloride solution, on the contrary, conducts electricity well because it contains many ions and they can move freely, including under the influence of electrical voltage.
To break ionic bonds in a crystal and hydrogen bonds in water, energy must be expended. When ions hydrate, energy is released. If the energy required to break bonds exceeds the energy released during ion hydration, then endothermic dissolution, and if vice versa, then – exothermic.
Sodium chloride dissolves in water with virtually zero thermal effect, therefore, the dissolution of this salt occurs only due to an increase in entropy. But usually dissolution is accompanied by a noticeable release of heat (Na 2 CO 3, CaCl 2, NaOH, etc.) or its absorption (KNO 3, NH 4 Cl, etc.), for example:

When water is evaporated from solutions resulting from chemical dissolution, dissolved substances are released again in a chemically unchanged form.

Both physical and chemical dissolution produce a solution of the substance that we dissolved, for example, a solution of sugar in water or a solution of sodium chloride in water. In other words, the solute can be released from the solution when water is removed.

HYDRATE COAT, HYDRATION, CHEMICAL DISSOLUTION.
Give three examples of substances that are well known to you: a) soluble in water or reacting with it, b) insoluble in water and not reacting with it.
2. What is a solvent and what is a dissolved substance (or substances) in the following solutions: a) soapy water, b) table vinegar, c) vodka d) hydrochloric acid, e) motorcycle fuel, f) pharmacy “hydrogen peroxide”, g) sparkling water, i) “greenback”, j) cologne?
If you have any difficulties, consult your parents.
3.List the ways in which solvent can be removed from a liquid solution.
4. How do you understand the expression “in a chemically unchanged form” in the last paragraph of the first paragraph of this chapter? What changes can occur to a substance as a result of its dissolution and subsequent release from solution?
5. It is known that fats are insoluble in water, but dissolve well in gasoline. Based on this, what can be said about the structure of fat molecules?
6. Write down the equations for the chemical dissolution of the following ionic substances in water:
a) silver nitrate, b) calcium hydroxide, c) cesium iodide, d) potassium carbonate, e) sodium nitrite, f) ammonium sulfate.
7.Write down the equations for the crystallization of substances from the solutions listed in task 6 when water is removed.
8. How do solutions obtained by physical dissolution of substances differ from solutions obtained by chemical dissolution? What do these solutions have in common?
9. Determine the mass of salt that must be dissolved in 300 ml of water to obtain a solution with a mass fraction of this salt equal to 0.1. The density of water is 1 g/ml, and the density of the solution is 1.05 g/ml. What is the concentration of salt in the resulting solution if its formula mass is 101 Dn?
10. How much water and barium nitrate do you need to take to prepare 0.5 l of a 0.1 M solution of this substance (solution density 1.02 g/ml)?
Experiments on dissolving ionic substances in water.

Any portion of sodium chloride (or other similar substance) placed in water would always dissolve completely if, in addition to the dissolution process

the reverse process would not occur - the process of crystallization of the initial substance from solution:

At the moment the crystal is placed in water, the rate of the crystallization process is zero, but as the concentration of ions in the solution increases, it increases and at some point becomes equal to the rate of dissolution. A state of equilibrium occurs:

the resulting solution is called saturated.

As such a characteristic, the mass fraction of a dissolved substance, its concentration or another physical quantity characterizing the composition of the solution can be used.
According to their solubility in a given solvent, all substances are divided into soluble, slightly soluble and practically insoluble. Usually practically insoluble substances are simply called insoluble. The solubility equal to 1 g in 100 g of H 2 O ( w 1%), and for the conventional boundary between sparingly soluble and insoluble substances - solubility equal to 0.1 g in 100 g H 2 O ( w 0,1%).
The solubility of a substance depends on temperature. Since solubility is a characteristic of equilibrium, its change with a change in temperature occurs in full accordance with Le Chatelier’s principle, that is, with exothermic dissolution of a substance, its solubility decreases with increasing temperature, and with endothermic dissolution it increases.
Solutions in which, under the same conditions, there is less dissolved substance than in saturated ones are called unsaturated.

SATURATED SOLUTION; UNSATURATED SOLUTION; SUBSTANCE SOLUBILITY; SOLUBLE, POORLY SOLUBLE AND INSOLUBLE SUBSTANCES.

1. Write down the equilibrium equations in the saturated solution – sediment system for a) potassium carbonate, b) silver nitrate and c) calcium hydroxide.
2. Determine the mass fraction of potassium nitrate in an aqueous solution of this salt saturated at 20 °C if, when preparing such a solution, 100 g of potassium nitrate was added to 200 g of water, and after completing the preparation of the solution, 36.8 g of potassium nitrate did not dissolve.
3. Is it possible to prepare an aqueous solution of potassium chromate K 2 CrO 4 at 20 ° C with a mass fraction of dissolved substance equal to 45%, if at this temperature no more than 63.9 g of this salt dissolves in 100 g of water.
4. The mass fraction of potassium bromide in a saturated aqueous solution at 0 °C is 34.5%, and at 80 °C – 48.8%. Determine the mass of potassium bromide released when 250 g of an aqueous solution of this salt saturated at 80°C is cooled to 0°C.
5. The mass fraction of calcium hydroxide in a saturated aqueous solution at 20 °C is 0.12%. How many liters of calcium hydroxide solution (limewater) saturated at this temperature can be obtained with 100 g of calcium hydroxide? Take the density of the solution equal to 1 g/ml.
6. At 25 °C, the mass fraction of barium sulfate in a saturated aqueous solution is 2.33·10 –2%. Determine the minimum volume of water required to completely dissolve 1 g of this salt.
preparation of saturated solutions.

Many substances, when they come into contact with water, enter into chemical reactions with it. As a result of this interaction, with an excess of water, as with dissolution, a solution is obtained. But if we remove water from this solution, we will not get the original substance.

What products are formed when a substance reacts chemically with water? It depends on the type of chemical bond in the substance; if the bonds are covalent, then the degree of polarity of these bonds. In addition, other factors also have an influence, some of which we will get acquainted with.

a) Compounds with ionic bonds

Most ionic compounds are either chemically soluble in water or insoluble. Standing apart are ionic hydrides and oxides, that is, compounds containing the same elements as water itself and some other substances. Let us consider the behavior of ionic oxides upon contact with water using the example of calcium oxide.
Calcium oxide, being an ionic substance, could chemically dissolve in water. In this case, calcium ions and oxide ions would pass into the solution. But a doubly charged anion is not the most stable valence state of the oxygen atom (if only because the affinity energy for the second electron is always negative, and the radius of the oxide ion is relatively small). Therefore, oxygen atoms tend to lower their formal charge. In the presence of water this is possible. The oxide ions that appear on the surface of the crystal interact with water molecules. This reaction can be represented in the form of a diagram showing its mechanism ( mechanism diagrams).

To better understand what is happening, let’s conditionally divide this process into stages:
1. The water molecule is turned towards the oxide ion by a hydrogen atom (oppositely charged).
2. The oxide ion shares a lone pair of electrons with the hydrogen atom; a covalent bond is formed between them (formed by a donor-acceptor mechanism).
3. The hydrogen atom has a single valence orbital (1 s) there are four electrons (two “old” and two “new”), which contradicts the Pauli principle. Therefore, the hydrogen atom gives a pair of bonding electrons ("old" electrons) to the oxygen atom, which is part of the water molecule, especially since this pair of electrons was already largely shifted to the oxygen atom. The bond between the hydrogen atom and the oxygen atom is broken.
4. Due to the formation of a bond via the donor-acceptor mechanism, the formal charge on the former oxide ion becomes equal to –1 e; on the oxygen atom, which was previously part of the water molecule, a charge appears, also equal to –1 e. This produces two hydroxide ions.
5. Calcium ions that are no longer bound by ionic bonds with oxide ions pass into solution and are hydrated:

The positive charge of calcium ions is “eroded” throughout the hydrated ion.
6. The resulting hydroxide ions are also hydrated:

The negative charge of the hydroxide ion is also “eroded.”
Total ionic equation for the reaction of calcium oxide with water
CaO cr + H 2 O Ca 2 aq+2OH aq .

Calcium ions and hydroxide ions appear in the solution in a ratio of 1:2. The same thing would happen if calcium hydroxide was dissolved in water. And indeed, by evaporating the water and drying the residue, we can obtain crystalline calcium hydroxide from this solution (but by no means an oxide!). Therefore, the equation for this reaction is often written as follows:

CaO cr + H 2 O = Ca(OH) 2р

and call " molecular"the equation of this reaction. In both equations, letter indices are sometimes not given, which often greatly complicates the understanding of the processes taking place, and is even simply misleading. At the same time, the absence of letter indices in equations is acceptable, for example, when solving calculation problems
In addition to calcium oxide, the following oxides also interact with water: Li 2 O, Na 2 O, K 2 O, Rb 2 O, Cs 2 O, SrO, BaO - that is, oxides of those metals that themselves react with water. All these oxides are classified as basic oxides. Other ionic oxides do not react with water.
Ionic hydrides, such as sodium hydride NaH, react with water in a completely similar way. The sodium ion only hydrates, and the hydride ion reacts with a water molecule:

As a result, sodium hydroxide remains in the solution.
The ionic equation for this reaction is

NaH cr + H 2 O = Na aq+OH aq+H2,

and the “molecular” equation is NaH cr + H 2 O = NaOH p + H 2.

b) Substances with metallic bonds

As an example, consider the interaction of sodium with water.

In the diagrams, a curved half-arrow means the transfer or movement of one electron

The sodium atom tends to give up its only valence electron. Once in water, it easily donates it to the hydrogen atom of the water molecule (it has a significant + on it) and turns into a sodium cation (Na). The hydrogen atom, having received an electron, becomes neutral (H · ) and can no longer hold on to the pair of electrons that binds it to the oxygen atom (remember the Pauli principle). This pair of electrons goes completely to the oxygen atom (in the water molecule it was already shifted towards it, but only partially). The oxygen atom acquires a formal charge A, the bond between the hydrogen and oxygen atoms breaks, and a hydroxide ion (O–H) is formed.
The fate of the resulting particles is different: the sodium ion interacts with other water molecules and, naturally, hydrates

just like the sodium ion, the hydroxide ion is hydrated, and the hydrogen atom, “waiting” for the appearance of another similar hydrogen atom, forms a hydrogen molecule 2H with it · = N 2.
Due to the non-polarity of its molecules, hydrogen is practically insoluble in water and is released from solution in the form of a gas. The ionic equation for this reaction is

2Na cr + 2H 2 O = 2Na aq+2OH aq+H2

a "molecular" –

2Na cr + 2H 2 O = 2NaOH p + H 2

Just like sodium, Li, K, Rb, Cs, Ca, Sr, Ba react violently with water at room temperature. When heated, Mg, as well as some other metals, react with it.

c) Substances with covalent bonds

Of the substances with covalent bonds, only those substances can react with water
a) the bonds in which are highly polar, which gives these substances some similarity to ionic compounds, or
b) which contain atoms that have a very high tendency to gain electrons.
Thus, they do not react with water and are insoluble in it (or very slightly soluble):
a) diamond, graphite, silicon, red phosphorus and other simple non-molecular substances;
b) silicon dioxide, silicon carbide and other complex non-molecular substances;
c) methane, heptane and other molecular substances with low-polar bonds;
d) hydrogen, sulfur, white phosphorus and other simple molecular substances, the atoms of which are not very inclined to attach electrons, as well as nitrogen, the molecules of which are very strong.
Of greatest importance is the interaction with water of molecular oxides, hydrides and hydroxides, and of simple substances - halogens.
We will look at how molecular oxides react with water using the example of sulfur trioxide:

The water molecule, due to one of the lone pairs of electrons of the oxygen atom, attacks the positively charged sulfur atom (+) and attaches to it with an O–S bond, and a formal charge B appears on the oxygen atom. Having received extra electrons, the sulfur atom ceases to hold the electron pair of one of -bonds, which completely passes to the corresponding oxygen atom, on which, due to this, a formal charge A arises. Then the lone pair of electrons of this oxygen atom is accepted by one of the hydrogen atoms that was part of the water molecule, which thus passes from one oxygen atom to another . As a result, a sulfuric acid molecule is formed. Reaction equation:

SO 3 + H 2 O = H 2 SO 4.

N2O5, P4O10 and some other molecular oxides react similarly, but somewhat more complexly, with water. All of them are acidic oxides.
N 2 O 5 + H 2 O = 2HNO 3;
P 4 O 10 + 6H 2 O = 4H 3 PO 4.

In all these reactions, acids are formed, which, in the presence of excess water, react with it. But, before considering the mechanism of these reactions, let’s look at how hydrogen chloride, a molecular substance with highly polar covalent bonds between hydrogen and chlorine atoms, reacts with water:

A polar hydrogen chloride molecule, once in water, is oriented as shown in the diagram (opposite charges of dipoles attract each other). The electron shell rarefied due to polarization (1 s-EO) of a hydrogen atom accepts a lone pair sp 3-hybrid electrons of the oxygen atom, and hydrogen joins the water molecule, completely giving the chlorine atom a pair of electrons that bonded these atoms in the hydrogen chloride molecule. As a result, the chlorine atom turns into a chloride ion, and the water molecule turns into an oxonium ion. Reaction equation:

HCl g + H 2 O = H 3 O aq+ Cl aq .

At low temperatures, crystalline oxonium chloride (H 3 O)Cl ( t pl = –15 °С).

The interaction of HCl and H 2 O can be imagined in another way:

that is, as a result of the transfer of a proton from a hydrogen chloride molecule to a water molecule. Therefore, it is an acid-base reaction.
Nitric acid interacts with water in a similar way.

which can also be represented as a proton transfer:

Acids containing several hydroxyl groups (OH groups) react with water in several stages (stepwise). An example is sulfuric acid.

The second proton is much more difficult to remove than the first, so the second stage of this process is reversible. By comparing the magnitude and distribution of charges in the sulfuric acid molecule and in the hydrosulfate ion, try to explain this phenomenon yourself.
When cooled, individual substances can be isolated from sulfuric acid solutions: (H 3 O)HSO 4 (t pl = 8.5 °C) and (H 3 O) 2 SO 4 (t pl = – 40 °C).
Anions formed from acid molecules after the abstraction of one or more protons are called acid residues.
Of the molecular simple substances, only F 2, Cl 2, Br 2 and, to an extremely small extent, I 2 react with water under normal conditions. Fluorine reacts violently with water, completely oxidizing it:

2F 2 + H 2 O = 2HF + OF 2.

At the same time, other reactions also occur.
The reaction of chlorine with water is much more important. Having a high propensity to add electrons (the molar energy of electron affinity of a chlorine atom is 349 kJ/mol), chlorine atoms partially retain it in the molecule (the molar energy of electron affinity of a chlorine molecule is 230 kJ/mol). Therefore, when dissolved, chlorine molecules hydrate, attracting oxygen atoms of water molecules. Some of these oxygen atoms have chlorine atoms that can accept a lone pair of electrons. The following is shown in the mechanism diagram:

The overall equation for this reaction is

Cl 2 + 2H 2 O = HClO + H 3 O + Cl.

But the reaction is reversible, so equilibrium is established:

Cl 2 + 2H 2 O HClO + H 3 O + Cl.

The resulting solution is called "chlorine water". Due to the presence of hypochlorous acid in it, it has strong oxidizing properties and is used as a bleaching and disinfectant.
Remembering that Cl and H3O are formed by the interaction (“dissolution”) of hydrogen chloride in water, we can write the “molecular” equation:

Cl 2 + H 2 O HClO p + HCl p.

Bromine reacts similarly with water, only the equilibrium in this case is greatly shifted to the left. Iodine practically does not react with water.

To imagine to what extent chlorine and bromine physically dissolve in water, and to what extent they react with it, we use the quantitative characteristics of solubility and chemical equilibrium.

The mole fraction of chlorine in an aqueous solution saturated at 20°C and atmospheric pressure is 0.0018, that is, for every 1000 molecules of water there are approximately 2 molecules of chlorine. For comparison, in a nitrogen solution saturated under the same conditions, the mole fraction of nitrogen is 0.000012, that is, one nitrogen molecule per approximately 100,000 water molecules. And to obtain a solution of hydrogen chloride saturated under the same conditions, for every 100 molecules of water you need to take about 35 molecules of hydrogen chloride. From this we can conclude that although chlorine is soluble in water, it is only slightly soluble. The solubility of bromine is slightly higher - approximately 4 molecules per 1000 molecules of water.

5. Give reaction equations that allow the following transformations to occur:

During the chemical dissolution of ionic substances, hydration of the ions passing into the solution occurs. Both cations and anions are hydrated. In general, hydrated cations are stronger than anions, and hydrated simple cations are stronger than complex cations. This is due to the fact that simple cations have free valence orbitals that can partially accept lone electron pairs of oxygen atoms included in water molecules.
When trying to isolate the starting substance from a solution by removing water, it is often not possible to obtain it. For example, if we dissolve colorless copper sulfate CuSO 4 in water, we will get a blue solution, which is given to it by hydrated copper ions:

After evaporating the solution (removing water) and cooling, blue crystals with the composition CuSO 4 5H 2 O will be released from it (the point between the formulas of copper sulfate and water means that for each formula unit of copper sulfate there are the number of water molecules indicated in the formula). The original copper sulfate can be obtained from this compound by heating it to 250 ° C. In this case, the reaction occurs:

CuSO 4 5H 2 O = CuSO 4 + 5H 2 O.

A study of the structure of CuSO 4·5H 2 O crystals showed that in its formula unit four water molecules are associated with a copper atom, and the fifth is associated with sulfate ions. Thus, the formula of this substance is SO 4 H 2 O, and it is called tetraaquacopper(II) sulfate monohydrate, or simply “copper sulfate”.
Four water molecules associated with a copper atom are the remainder of the hydration shell of the Cu 2 ion aq, and the fifth water molecule is the remainder of the hydration shell of the sulfate ion.
The compound SO 4 H 2 O – hexaquatic iron(II) sulfate monohydrate, or “iron sulfate” – has a similar structure.
Other examples:
Cl – hexaaquacalcium chloride;
Cl 2 – hexaquamagnesium chloride.
These and similar substances are called crystal hydrates, and the water they contain is water of crystallization.
Often the structure of the crystalline hydrate is unknown, or it cannot be expressed by conventional formulas. In these cases, the above-mentioned "dotted formulas" and simplified names are used for crystalline hydrates, for example:
CuSO 4·5H 2 O – copper sulfate pentahydrate;
Na 2 CO 3 10H 2 O – sodium carbonate decahydrate;
AlCl 3· 6H 2 O – aluminum chloride hexahydrate.

When crystalline hydrates are formed from starting substances and water, O-H bonds do not break in water molecules.

If the water of crystallization is held in the crystal hydrate by weak intermolecular bonds, then it is easily removed when heated:
Na 2 CO 3 10H 2 O = Na 2 CO 3 + 10H 2 O (at 120 ° C);
K 2 SO 3 2H 2 O = K 2 SO 3 + 2H 2 O (at 200 ° C);
CaCl 2 6H 2 O = CaCl 2 + 6H 2 O (at 250 ° C).

If in a crystalline hydrate the bonds between water molecules and other particles are close to chemical, then such a crystalline hydrate either dehydrates (loses water) at a higher temperature, for example:
Al 2 (SO 4) 3 18H 2 O = Al 2 (SO 4) 3 + 18H 2 O (at 420 ° C);
CoSO 4 7H 2 O = CoSO 4 + 7H 2 O (at 410 ° C);

or when heated, decomposes to form other chemicals, for example:
2(FeCl 3 6H 2 O) = Fe 2 O 3 + 6HCl + 9H 2 O (above 250 ° C);
2(AlCl 3 6H 2 O) = Al 2 O 3 + 6HCl + 9H 2 O (200 – 450 ° C).

Thus, the interaction of anhydrous substances forming crystalline hydrates with water can be either chemical dissolution or a chemical reaction.

CRYSTAL HYDRATES
Determine the mass fraction of water in a) copper sulfate pentahydrate, b) sodium hydroxide dihydrate, c) KAl(SO 4) 2 12H 2 O (potassium alum).
2. Determine the composition of magnesium sulfate crystalline hydrate if the mass fraction of water in it is 51.2%. 3. What is the mass of water released during the calcination of sodium sulfate decahydrate (Na 2 SO 4 10H 2 O) weighing 644 g?
4.How much anhydrous calcium chloride can be obtained by calcining 329 g of calcium chloride hexahydrate?
5. Calcium sulfate dihydrate CaSO 4 · 2H 2 O when heated to 150 ° C loses 3/4 of its water. Make up a formula for the resulting crystalline hydrate (alabaster) and write down the equation for the transformation of gypsum into alabaster.
6. Determine the mass of copper sulfate and water that must be taken to prepare 10 kg of a 5% solution of copper sulfate.
7. Determine the mass fraction of iron(II) sulfate in the solution obtained by mixing 100 g of iron sulfate (FeSO 4 7H 2 O) with 9900 g of water.
Preparation and decomposition of crystalline hydrates.

The most important substance of our planet, unique in its properties and composition, is, of course, water. After all, it is thanks to her that there is life on Earth, while there is no life on other objects of the solar system known today. Solid, liquid, in the form of steam - any of it is needed and important. Water and its properties form the subject of study of an entire scientific discipline - hydrology.

The amount of water on the planet

If we consider the indicator of the amount of this oxide in all states of aggregation, then it is about 75% of the total mass on the planet. In this case, one should take into account bound water in organic compounds, living things, minerals and other elements.

If we take into account only the liquid and solid states of water, the figure drops to 70.8%. Let's consider how these percentages are distributed, where the substance in question is contained.

1. There is 360 million km 2 of salt water in the oceans and seas, and saline lakes on Earth.
2. Fresh water is distributed unevenly: 16.3 million km 2 of it is encased in ice in the glaciers of Greenland, the Arctic, and Antarctica.
3. 5.3 million km 2 of hydrogen oxide is concentrated in fresh rivers, swamps and lakes.
4. Groundwater amounts to 100 million m3.

That is why astronauts from distant outer space can see the Earth in the shape of a blue ball with rare inclusions of land. Water and its properties, knowledge of its structural features are important elements of science. In addition, recently humanity has begun to experience a clear shortage of fresh water. Perhaps such knowledge will help in solving this problem.

Composition of water and molecular structure

If we consider these indicators, the properties that this amazing substance exhibits will immediately become clear. Thus, a water molecule consists of two hydrogen atoms and one oxygen atom, therefore it has the empirical formula H 2 O. In addition, the electrons of both elements play an important role in the construction of the molecule itself. Let's see what the structure of water and its properties are.

It is obvious that each molecule is oriented around the other, and together they form a common crystal lattice. It is interesting that the oxide is built in the shape of a tetrahedron - an oxygen atom in the center, and two pairs of electrons and two hydrogen atoms around it asymmetrically. If you draw lines through the centers of the atomic nuclei and connect them, you will get exactly a tetrahedral geometric shape.

The angle between the center of the oxygen atom and the hydrogen nuclei is 104.5 0 C. O-H bond length = 0.0957 nm. The presence of electron pairs of oxygen, as well as its greater electron affinity compared to hydrogen, ensures the formation of a negatively charged field in the molecule. In contrast, the hydrogen nuclei form the positively charged part of the compound. Thus, it turns out that the water molecule is a dipole. This determines what water can be, and its physical properties also depend on the structure of the molecule. For living beings, these features play a vital role.

Basic physical properties

These usually include the crystal lattice, boiling and melting points, and special individual characteristics. Let's consider all of them.

1. The structure of the crystal lattice of hydrogen oxide depends on the state of aggregation. It can be solid - ice, liquid - basic water under normal conditions, gaseous - steam when the water temperature rises above 100 0 C. Ice forms beautiful patterned crystals. The lattice as a whole is loose, but the connection is very strong and the density is low. You can see it in the example of snowflakes or frosty patterns on glass. In ordinary water, the lattice does not have a constant shape; it changes and passes from one state to another.
2. A water molecule in outer space has a regular spherical shape. However, under the influence of the earth's gravity, it is distorted and in a liquid state takes the form of a vessel.
3. The fact that hydrogen oxide is a dipole in structure determines the following properties: high thermal conductivity and heat capacity, which can be seen in the rapid heating and long cooling of the substance, the ability to orient both ions and individual electrons and compounds around itself. This makes water a universal solvent (both polar and neutral).
4. The composition of water and the structure of the molecule explain the ability of this compound to form multiple hydrogen bonds, including with other compounds that have lone electron pairs (ammonia, alcohol, and others).
5. The boiling point of liquid water is 100 0 C, crystallization occurs at +4 0 C. Below this indicator there is ice. If you increase the pressure, the boiling point of water will increase sharply. So, at high atmospheres it is possible to melt lead in it, but it will not even boil (over 300 0 C).
6. The properties of water are very significant for living beings. For example, one of the most important is surface tension. This is the formation of a thin protective film on the surface of hydrogen oxide. We are talking about liquid water. It is very difficult to break this film by mechanical action. Scientists have determined that a force equal to the weight of 100 tons will be required. How to spot it? The film is obvious when water drips slowly from the faucet. It can be seen that it is as if in some kind of shell, which is stretched to a certain limit and weight and comes off in the form of a round droplet, slightly distorted by gravity. Thanks to surface tension, many objects can float on the surface of water. Insects with special adaptations can move freely along it.
7. Water and its properties are anomalous and unique. According to organoleptic indicators, this compound is a colorless liquid without taste or odor. What we call the taste of water is the minerals and other components dissolved in it.
8. The electrical conductivity of hydrogen oxide in the liquid state depends on how many and what salts are dissolved in it. Distilled water, which does not contain any impurities, does not conduct electric current.

Ice is a special state of water. In the structure of this state, the molecules are connected to each other by hydrogen bonds and form a beautiful crystal lattice. But it is quite unstable and can easily split, melt, that is, become deformed. There are many voids between the molecules, the dimensions of which exceed the dimensions of the particles themselves. Due to this, the density of ice is less than that of liquid hydrogen oxide.

This is of great importance for rivers, lakes and other fresh water bodies. Indeed, in winter, the water in them does not freeze completely, but is only covered with a dense crust of lighter ice that floats to the top. If this property were not characteristic of the solid state of hydrogen oxide, then the reservoirs would freeze through. Life under water would be impossible.

In addition, the solid state of water is of great importance as a source of huge amounts of fresh drinking water. These are glaciers.

A special property of water can be called the triple point phenomenon. This is a state in which ice, steam and liquid can exist simultaneously. This requires the following conditions:

• high pressure - 610 Pa;
• temperature 0.01 0 C.

Water clarity varies depending on foreign matter. The liquid can be completely transparent, opalescent, or cloudy. Waves of yellow and red colors are absorbed, violet rays penetrate deeply.

Chemical properties

Water and its properties are an important tool in understanding many life processes. Therefore they have been studied very well. Thus, hydrochemistry is interested in water and its chemical properties. Among them are the following:

1. Rigidity. This is a property that is explained by the presence of calcium and magnesium salts and their ions in solution. It is divided into permanent (salts of the named metals: chlorides, sulfates, sulfites, nitrates), temporary (bicarbonates), which is eliminated by boiling. In Russia, water is chemically softened before use for better quality.
2. Mineralization. A property based on the dipole moment of hydrogen oxide. Thanks to its presence, molecules are able to attach to themselves many other substances, ions and hold them. This is how associates, clathrates and other associations are formed.
3. Redox properties. As a universal solvent, catalyst, and associate, water is capable of interacting with many simple and complex compounds. With some it acts as an oxidizing agent, with others - vice versa. As a reducing agent it reacts with halogens, salts, some less active metals, and with many organic substances. Organic chemistry studies the latest transformations. Water and its properties, in particular chemical ones, show how universal and unique it is. As an oxidizing agent, it reacts with active metals, some binary salts, many organic compounds, carbon, and methane. In general, chemical reactions involving a given substance require the selection of certain conditions. The outcome of the reaction will depend on them.
4. Biochemical properties. Water is an integral part of all biochemical processes in the body, being a solvent, catalyst and medium.
5. Interaction with gases to form clathrates. Ordinary liquid water can absorb even chemically inactive gases and place them inside cavities between the molecules of the internal structure. Such compounds are usually called clathrates.
6. With many metals, hydrogen oxide forms crystalline hydrates, in which it is included unchanged. For example, copper sulfate (CuSO 4 * 5H 2 O), as well as ordinary hydrates (NaOH * H 2 O and others).
7. Water is characterized by compound reactions in which new classes of substances (acids, alkalis, bases) are formed. They are not redox.
8. Electrolysis. Under the influence of an electric current, the molecule decomposes into its component gases - hydrogen and oxygen. One of the ways to obtain them is in the laboratory and industry.

From the point of view of Lewis's theory, water is a weak acid and a weak base at the same time (ampholyte). That is, we can talk about a certain amphotericity in chemical properties.

Water and its beneficial properties for living beings

It is difficult to overestimate the importance that hydrogen oxide has for all living things. After all, water is the very source of life. It is known that without it a person could not live even a week. Water, its properties and significance are simply colossal.

1. It is a universal solvent, that is, capable of dissolving both organic and inorganic compounds, acting in living systems. That is why water is the source and medium for all catalytic biochemical transformations to occur, with the formation of complex vital complex compounds.
2. The ability to form hydrogen bonds makes this substance universal in withstanding temperatures without changing its state of aggregation. If this were not so, then with the slightest decrease in degrees it would turn into ice inside living beings, causing cell death.
3. For humans, water is the source of all basic household goods and needs: cooking, washing, cleaning, bathing, bathing and swimming, etc.
4. Industrial plants (chemical, textile, engineering, food, oil refining and others) would not be able to carry out their work without the participation of hydrogen oxide.
5. Since ancient times it was believed that water is a source of health. It was and is used today as a medicinal substance.
6. Plants use it as their main source of nutrition, due to which they produce oxygen, the gas that allows life to exist on our planet.

We can name dozens more reasons why water is the most widespread, important and necessary substance for all living and artificially created objects. We have cited only the most obvious, main ones.

Hydrological cycle of water

In other words, this is its cycle in nature. A very important process that allows us to constantly replenish dwindling water supplies. How does it happen?

There are three main participants: underground (or groundwater) water, surface water and the World Ocean. The atmosphere, which condenses and produces precipitation, is also important. Also active participants in the process are plants (mainly trees), capable of absorbing huge amounts of water per day.

So, the process goes as follows. Groundwater fills underground capillaries and flows to the surface and the World Ocean. Surface water is then absorbed by plants and transpired into the environment. Evaporation also occurs from vast areas of oceans, seas, rivers, lakes and other bodies of water. Once in the atmosphere, what does water do? It condenses and flows back in the form of precipitation (rain, snow, hail).

If these processes had not occurred, then water supplies, especially fresh water, would have run out long ago. That is why people pay great attention to the protection and normal hydrological cycle.

Concept of heavy water

In nature, hydrogen oxide exists as a mixture of isotopologues. This is due to the fact that hydrogen forms three types of isotopes: protium 1 H, deuterium 2 H, tritium 3 H. Oxygen, in turn, also does not lag behind and forms three stable forms: 16 O, 17 O, 18 O. It is thanks to Therefore, there is not just ordinary protium water of the composition H 2 O (1 H and 16 O), but also deuterium and tritium.

At the same time, it is deuterium (2 H) that is stable in structure and form, which is included in the composition of almost all natural waters, but in small quantities. This is what they call heavy. It is somewhat different from normal or light in all respects.

Heavy water and its properties are characterized by several points.

1. Crystallizes at a temperature of 3.82 0 C.
2. Boiling is observed at 101.42 0 C.
3. The density is 1.1059 g/cm3.
4. As a solvent it is several times worse than light water.
5. It has the chemical formula D 2 O.

When conducting experiments showing the influence of such water on living systems, it was found that only some types of bacteria are capable of living in it. It took time for the colonies to adapt and acclimatize. But, having adapted, they completely restored all vital functions (reproduction, nutrition). In addition, steel is very resistant to radiation. Experiments on frogs and fish did not give a positive result.

Modern areas of application of deuterium and the heavy water formed by it are nuclear and nuclear energy. Such water can be obtained in laboratory conditions using ordinary electrolysis - it is formed as a by-product. Deuterium itself is formed during repeated distillations of hydrogen in special devices. Its use is based on its ability to slow down neutron fusions and proton reactions. It is heavy water and hydrogen isotopes that are the basis for creating nuclear and hydrogen bombs.

Experiments on the use of deuterium water by people in small quantities have shown that it does not linger for long - complete withdrawal is observed after two weeks. It cannot be used as a source of moisture for life, but its technical significance is simply enormous.

Melt water and its use

Since ancient times, the properties of such water have been identified by people as healing. It has long been noticed that when the snow melts, animals try to drink water from the resulting puddles. Later, its structure and biological effects on the human body were carefully studied.

Melt water, its characteristics and properties are in the middle between ordinary light water and ice. From the inside, it is formed not just by molecules, but by a set of clusters formed by crystals and gas. That is, inside the voids between the structural parts of the crystal there are hydrogen and oxygen. In general, the structure of melt water is similar to the structure of ice - the structure is preserved. The physical properties of such hydrogen oxide change slightly compared to conventional ones. However, the biological effect on the body is excellent.

When water is frozen, the first fraction turns into ice the heavier part - these are deuterium isotopes, salts and impurities. Therefore, this core should be removed. But the rest is clean, structured and healthy water. What is the effect on the body? Scientists from the Donetsk Research Institute named the following types of improvements:

1. Acceleration of recovery processes.
2. Strengthening the immune system.
3. In children, after inhalation of this water, colds are restored and cured, coughs, runny noses, etc. go away.
4. Breathing, condition of the larynx and mucous membranes improves.
5. The general well-being of a person and activity increase.

Today there are a number of supporters of treatment with melt water who write their positive reviews. However, there are scientists, including doctors, who do not support these views. They believe that there will be no harm from such water, but there is little benefit either.

Energy

Why can the properties of water change and be restored when transitioning to different states of aggregation? The answer to this question is as follows: this compound has its own information memory, which records all changes and leads to the restoration of structure and properties at the right time. The bioenergy field through which part of the water passes (that which comes from space) carries a powerful charge of energy. This pattern is often used in treatment. However, from a medical point of view, not every water can have a beneficial effect, including informational.

Structured water - what is it?

This is water that has a slightly different structure of molecules, the arrangement of crystal lattices (the same as that observed in ice), but it is still a liquid (melt also belongs to this type). In this case, the composition of water and its properties, from a scientific point of view, do not differ from those characteristic of ordinary hydrogen oxide. Therefore, structured water cannot have such a broad healing effect that esotericists and supporters of alternative medicine attribute to it.