Hydrogen oxide (H 2 O), much better known to all of us under the name “water,” without exaggeration, is the main liquid in the life of organisms on Earth, since all chemical and biological reactions take place either with the participation of water or in solutions.

Water is the second most important substance for the human body, after air. A person can live without water for no more than 7-8 days.

Pure water in nature can exist in three states of aggregation: solid - in the form of ice, liquid - water itself, in gaseous - in the form of steam. No other substance can boast such a variety of states of aggregation in nature.

Physical properties of water

• at no. - it is a colorless, odorless and tasteless liquid;
• water has high heat capacity and low electrical conductivity;
• melting point 0°C;
• boiling point 100°C;
• the maximum density of water at 4°C is 1 g/cm 3 ;
• water is a good solvent.

Structure of a water molecule

A water molecule consists of one oxygen atom, which is connected to two hydrogen atoms, with O-H bonds forming an angle of 104.5°, while the shared electron pairs are shifted towards the oxygen atom, which is more electronegative compared to hydrogen atoms, therefore, on A partial negative charge is formed on the oxygen atom, and a positive charge is formed on the hydrogen atoms. Thus, a water molecule can be considered as a dipole.

Water molecules can form hydrogen bonds with each other, being attracted by oppositely charged parts (hydrogen bonds are shown with dotted lines in the figure):

The formation of hydrogen bonds explains the high density of water, its boiling and melting points.

The number of hydrogen bonds depends on the temperature - the higher the temperature, the fewer bonds are formed: in water vapor there are only individual molecules; in the liquid state, associates (H 2 O) n are formed; in the crystalline state, each water molecule is connected to neighboring molecules by four hydrogen bonds.

Chemical properties of water

Water “willingly” reacts with other substances:

• Water reacts with alkali and alkaline earth metals at zero conditions: 2Na+2H 2 O = 2NaOH+H 2
• Water reacts with less active metals and non-metals only at high temperatures: 3Fe+4H 2 O=FeO → Fe 2 O 3 +4H 2 C+2H 2 O → CO 2 +2H 2
• with basic oxides at no. water reacts to form bases: CaO+H 2 O = Ca(OH) 2
• with acid oxides at no. water reacts to form acids: CO 2 + H 2 O = H 2 CO 3
• water is the main participant in hydrolysis reactions (for more details, see Hydrolysis of Salts);
• water participates in hydration reactions by joining organic substances with double and triple bonds.

Solubility of substances in water

• highly soluble substances - more than 1 g of substance dissolves in 100 g of water at standard conditions;
• poorly soluble substances - 0.01-1 g of substance dissolves in 100 g of water;
• practically insoluble substances - less than 0.01 g of substance dissolves in 100 g of water.

There are no completely insoluble substances in nature.

Water (hydrogen oxide) is the simplest stable compound of hydrogen and oxygen. The molecular weight of water is 18.0160. Hydrogen accounts for 11.19% by mass, and oxygen – 88.81%. In nature, there are three isotopes of hydrogen - light hydrogen H1, deuterium D (H2) and tritium (H3) and three isotopes of oxygen – O16, O17, O18. Two more isotopes of hydrogen and six isotopes of oxygen have been artificially obtained. Theoretically, five isotopes of hydrogen and nine isotopes of oxygen can form 135 varieties of water molecules, of which nine are stable, including stable isotopes. In natural water, the share of H 1/2 O 16 accounts for 99.75% by weight, the share of H 1/2 O 18 is 0.2%, the share of H 1/2 O 17 is 0.04%, and the share of H 1 H 2 O 16 – approximately 0.093%. the remaining five varieties are present in negligible quantities.

The water molecule has an angular structure. The nuclei of atoms form an isosceles triangle, at the base of which there are two protons, and at the apex - the nucleus of an oxygen atom. The internuclear O-H distance is close to 0.1 nm, and the distance between the nuclei of hydrogen atoms is approximately 0.15 nm. The structural formula of water is:

The eight electrons in the outer electron layer of the oxygen atom form four electron pairs, two of which create covalent O-H bonds and the other two are lone electron pairs. Due to the displacement of electrons forming O-H bonds towards the oxygen atom, the hydrogen atoms acquire effective positive charges. The lone pairs of electrons are also shifted relative to the nucleus of the oxygen atom and create two negative poles.

Measurements of the molecular weight of liquid water (18.016) showed that it is higher than the molecular weight of water in the vapor state; this indicates the association of molecules - their combination into complex aggregates. This phenomenon is confirmed by the abnormally high melting and boiling temperatures of water. The association of water molecules is due to the formation of hydrogen bonds. In the solid state, the oxygen atom of each water molecule forms two hydrogen bonds with neighboring molecules.

Pure natural water is a liquid without odor, taste or color. Compared to other chemical compounds, water exhibits unusual deviations in a number of physical properties - density, specific heat, viscosity, etc.

When water is heated, hydrogen bonds are broken and the degree of association of water molecules decreases. Of great importance is the fact that water has an abnormally high heat capacity - 4.18 J/(g*K). The high heat capacity of water is a consequence of the consumption of part of the heat to break hydrogen bonds. Under natural conditions, water cools slowly and warms up slowly, acting as a temperature regulator on Earth.

The boiling point of water is directly dependent on pressure - the higher it is, the higher the boiling point.

The viscosity (the ability of a liquid to resist various forms of movement) of water naturally changes depending on the temperature: it decreases with its increase. As the concentration of salts dissolved in water increases, the viscosity of water increases. At the same time, the effect of pressure on the viscosity of water is quite specific: with decreasing temperature at moderate pressure, the viscosity decreases.

The surface tension of water decreases with increasing temperature. This surface tension ensures that the water level in a capillary tube with a diameter of 0.1 mm rises by 15 cm at t = 18 o C. When salts are added, the surface tension of water increases, but only slightly.

Due to the asymmetric structure, the water molecule has a pronounced dipole character, i.e. In a molecule, the centers of gravity of positive and negative charges do not coincide. The dipole nature of water molecules contributes to the formation of so-called addition products: molecules of substances of ionic structure or non-ionic, but with a pronounced dipole character, are added to water molecules.

The relative dielectric constant of water is 80 - this is a very high value, which explains such a high ionizing force of water.

The optical properties of water are assessed by its transparency, which in turn depends on the wavelength of the beam passing through the water.

Water is a thermally stable substance. It can withstand heating up to a temperature of 1000 o C and only at temperatures above 1000 o C it partially decomposes into hydrogen and oxygen. Thermal decomposition (dissociation) of water occurs with the absorption of heat, and according to Le Chatelier's principle, the higher the temperature, the greater the degree of dissociation.

Water is a very reactive substance. It reacts with oxides of many metals (Na 2 O, CaO, etc.) and non-metals (Cl 2 O, CO 2, etc.), forming crystalline hydrates with some salts, and interacts with active metals (Na, K, etc.).

Water is a catalyst for many chemical reactions, and sometimes at least traces of it are necessary for a reaction to occur.

Having a dipole character, water is a solvent. A solution is a solid or liquid homogeneous system consisting of two or more components. The most common are liquid solutions, when one of the components of the system is a liquid, and of all liquid solutions, aqueous solutions are of paramount importance. The energy of formation of water molecules is high, it is 242 kJ/mol. This explains the stability of water in natural conditions. Stability, combined with electrical characteristics and molecular structure, make water an almost universal solvent for many substances.

Chemically pure water conducts electricity very poorly, but still has some electrical conductivity, since it is capable of dissociating to a very small extent into hydrogen ions and hydroxyl ions: H 2 O  H + + OH -

Since the rate of a chemical reaction is directly proportional to the effective masses, i.e. concentrations of reactants, so we can write:

V 1 = k 1 and v 2 = k 2 *

For water and dilute solutions at a constant temperature, the product of the concentrations of hydrogen ions and hydroxyl ions is a constant value. Solutions in which the concentrations of hydrogen and hydroxy ions are the same are called neutral solutions. If the solution contains > and, therefore, > mol/l, then such a solution is called acidic, and if< моль/л, то раствор называется щелочным. Большинство химических элементов образует более растворимые соединения в кислых средах и менее растворимые в нейтральных. Некоторые элементы образуют легкорастворимые соединения в щелочных растворах. Так, двухвалентное железо может находиться в растворе в менее кислых водах, чем трехвалентное. Гидроксиды магния выпадают из раствора только в сильнощелочных водах. Важной характеристикой миграционной способности элементов является «рН начала выпадения гидроксида». То есть та величина рН раствора, при которой из раствора начинается выпадение гидроксида данного элемента. Эта величина зависит как от свойств самого элемента, так и от условий внешней среды. Например, для большинства элементов с повышением температуры рН осаждения гидроксида повышается. Поэтому в ландшафтах жаркого климата миграционная способность элементов в водной среде может быть более высокой, чем в условиях низких температур.

Among the anomalous properties of water that play an important role in maintaining life on our planet, it should be noted:

Anomalous form of temperature dependence of water density. The maximum density of water is observed at a temperature of about 4 o C. Due to this, with the onset of frost, the surface layer of water cools to 4 o C and, as a heavier layer, sinks to the bottom of the reservoir, displacing warmer and lighter layers to the surface. In the future, when the entire reservoir cools to 4 o C, only the surface layer will cool, which, being lighter, will remain on the surface of the reservoir. Ice and the snow covering it are good protection for a reservoir from freezing, since they have low thermal conductivity (the thermal conductivity of snow at a density of 0.1 g/cm 3 corresponds to the thermal conductivity of wool, and at a density of 0.2 g/cm 3 it corresponds to the thermal conductivity of paper). All this generally contributes to the preservation of life in reservoirs in winter.

Heat capacity of water. The heat capacity of water is higher than that of all solid and liquid substances, with the exception of liquid ammonia and hydrogen. Thanks to their enormous heat capacity, the oceans smooth out temperature fluctuations, and the temperature difference from the equator to the pole is only 30 o C.

Heat of Melting.

The heat of fusion of water, 6.012 kJ/mol, is the highest among solids and liquids, with the exception of ammonia and hydrogen. Due to the high heat of fusion, seasonal transitions on Earth are smoothed out: spring and autumn can be considered as a phase transition of water. Relatively easily heated or cooled to 0 o C, water, snow and ice require significant energy expenditure to transition to another phase state. Therefore, these transitions usually extend over time. It should be noted, for example, that when 1 m 3 of water freezes, the same amount of heat is released as when burning approximately 10 kg of coal. Heat of vaporization

..

The maximum surface tension of water, with the exception of mercury, leads to the appearance of ripples and waves on the water surface even with a weak wind. As a result, the area of ​​the water surface sharply increases and the processes of heat transfer between the atmosphere and the hydrosphere intensify. High surface tension of water is also associated with capillary forces, thanks to which water can rise to a height of 10-12 meters from the groundwater level. Dielectric constant

.

The dielectric constant has an abnormally high value. This determines the greatest dissolving ability of water in relation to substances with a polar and ionic structure. Therefore, there is no chemically pure water in nature.

We always deal with its solutions.

CHEMICAL AND PHYSICAL PROPERTIES OF WATER

At the temperature of transition to the solid state, water molecules are ordered, during this process the volumes of voids between the molecules increase, and the overall density of water decreases, which explains the reason for the lower density (larger volume) of water in the ice phase. During evaporation, on the contrary, all bonds are broken. Breaking bonds requires a lot of energy, which is why water has the highest specific heat of any liquid or solid. In order to heat one liter of water by one degree, 4.1868 kJ of energy is required. Due to this property, water is often used as a coolant. In addition to its high specific heat capacity, water also has high specific heats of fusion (at 0 °C - 333.55 kJ/kg) and vaporization (2250 kJ/kg).

Chemical properties. Water is the most common solvent on planet Earth, which largely determines the nature of terrestrial chemistry as a science. Most of chemistry, at its inception as a science, began precisely as the chemistry of aqueous solutions of substances. Among the chemical properties of water, the ability of its molecules to dissociate (disintegrate) into ions and the ability of water to dissolve substances of different chemical nature are especially important.

Dissociation (decay) of water molecules into ions:

H2O > H++OH, or 2H2O > H3O (hydroxy ion) +OH

The reactivity of water is relatively low. True, some active metals are capable of displacing hydrogen from it:

2Na+2H2O > 2NaOH+H2^,

and in an atmosphere of free fluorine, water can burn:

2F2+2H 2O > 4HF+O2.

Water reacts at room temperature:

1) with active metals (sodium, potassium, calcium, barium, etc.)

2H2O + 2Na > 2NaOH + H2

2) with fluorine and interhalide compounds

2H2O + 2F2 > 4HF + O2

3) with salts formed by a weak acid and a weak base, causing their complete hydrolysis:

Al2S3 +6H2O > 2Al(OH)3 + 3H2S

4) with anhydrides and acid halides of carboxylic and inorganic acids

5) with active organometallic compounds (diethylzinc, Grignard reagents, methyl sodium, etc.)

6) with carbides, nitrides, phosphides, silicides, hydrides of active metals (calcium, sodium, lithium, etc.)

7) with many salts, forming hydrates

8) with boranes, silanes

9) with ketenes, carbon dioxide

Water reacts when heated:

1) with iron, magnesium:

2) with coal, methane:

3) with some alkyl halides

Water reacts in the presence of a catalyst:

4) with amides, esters of carboxylic acids

5) with acetylene and other alkynes

6) with alkenes

7) with nitriles

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DEFINITION

Water– hydrogen oxide is a binary compound of inorganic nature.

Formula – H 2 O. Molar mass – 18 g/mol. It can exist in three states of aggregation - liquid (water), solid (ice) and gaseous (water vapor).

Chemical properties of water

Water is the most common solvent. There is an equilibrium in a water solution, which is why water is called an ampholyte:

H 2 O ↔ H + + OH — ↔ H 3 O + + OH — .

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

H 2 O = H 2 + O 2.

At room temperature, water dissolves active metals to form alkalis, and hydrogen is also released:

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

Water is able to interact with fluorine and interhalide compounds, and in the second case the reaction occurs at low temperatures:

2H 2 O + 2F 2 = 4HF + O 2.

3H 2 O +IF 5 = 5HF + HIO 3.

Salts formed by a weak base and a weak acid undergo hydrolysis when dissolved in water:

Al 2 S 3 + 6H 2 O = 2Al(OH) 3 ↓ + 3H 2 S.

Water can dissolve certain substances, metals and non-metals, when heated:

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

H 2 O + C ↔ CO + H 2.

Water, in the presence of sulfuric acid, enters into interaction reactions (hydration) with unsaturated hydrocarbons - alkenes with the formation of saturated monohydric alcohols:

CH 2 = CH 2 + H 2 O → CH 3 -CH 2 -OH.

Physical properties of water

Water is a clear liquid (n.s.). The dipole moment is 1.84 D (due to the strong difference in the electronegativities of oxygen and hydrogen). Water has the highest specific heat capacity among all substances in liquid and solid aggregate states. The specific heat of fusion of water is 333.25 kJ/kg (0 C), vaporization is 2250 kJ/kg. Water can dissolve polar substances. Water has high surface tension and a negative surface electrical potential.

Getting water

Water is obtained by a neutralization reaction, i.e. reactions between acids and alkalis:

H 2 SO 4 + 2KOH = K 2 SO 4 + H 2 O;

HNO 3 + NH 4 OH = NH 4 NO 3 + H 2 O;

2CH 3 COOH + Ba(OH) 2 = (CH 3 COO) 2 Ba + H 2 O.

One of the ways to obtain water is the reduction of metals with hydrogen from their oxides:

CuO + H 2 = Cu + H 2 O.

Examples of problem solving

EXAMPLE 1

Exercise	How much water do you need to take to prepare a 5% solution from a 20% acetic acid solution?
Solution	According to the definition of the mass fraction of a substance, a 20% acetic acid solution is 80 ml of solvent (water) 20 g of acid, and a 5% acetic acid solution is 95 ml of solvent (water) 5 g of acid. Let's make a proportion: x = 20 × 95 /5 = 380. Those. the new solution (5%) contains 380 ml of solvent. It is known that the initial solution contained 80 ml of solvent. Therefore, to obtain a 5% solution of acetic acid from a 20% solution, you need to add: 380-80 = 300 ml of water.
Answer	You need 300 ml of water.

EXAMPLE 2

Exercise	When an organic substance weighing 4.8 g was burned, 3.36 liters of carbon dioxide (CO) and 5.4 g of water were formed. The hydrogen density of organic matter is 16. Determine the formula of organic matter.
Solution	Molar masses of carbon dioxide and water, calculated using the table of chemical elements by D.I. Mendeleev – 44 and 18 g/mol, respectively. Let's calculate the amount of substance in the reaction products: n(CO 2) = V(CO 2) / V m; n(H 2 O) = m(H 2 O) / M(H 2 O); n(CO 2) = 3.36 / 22.4 = 0.15 mol; n(H 2 O) = 5.4 / 18 = 0.3 mol. Considering that the CO 2 molecule contains one carbon atom, and the H 2 O molecule contains 2 hydrogen atoms, the amount of substance and mass of these atoms will be equal to: n(C) = 0.15 mol; n(H) = 2×0.3 mol; m(C) = n(C)× M(C) = 0.15 × 12 = 1.8 g; m(N) = n(N)× M(N) = 0.3 × 1 = 0.3 g. Let's determine whether the organic substance contains oxygen: m(O) = m(C x H y O z) – m(C) – m(H) = 4.8 – 0.6 – 1.8 = 2.4 g. Amount of substance of oxygen atoms: n(O) = 2.4 / 16 = 0.15 mol. Then, n(C): n(H): n(O) = 0.15: 0.6: 0.15. Divide by the smallest value, we get n(C):n(H): n(O) = 1: 4: 1. Therefore, the formula of the organic substance is CH 4 O. The molar mass of the organic substance calculated using the table of chemical elements D.I. Mendeleev – 32 g/mol. Molar mass of an organic substance, calculated using its hydrogen density: M(C x H y O z) = M(H 2) × D(H 2) = 2 × 16 = 32 g/mol. If the formulas of an organic substance derived from combustion products and using hydrogen density differ, then the ratio of molar masses will be greater than 1. Let's check this: M(C x H y O z) / M(CH 4 O) = 1. Therefore, the formula of the organic substance is CH 4 O.
Answer	The formula of organic matter is CH 4 O.

WATER

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

The angle of 104.5° between the bonds in a water molecule determines the friability of ice and liquid water and, as a consequence, the anomalous dependence of density on temperature. This is why large bodies of water do not freeze to the bottom, which makes life possible in them.

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 extremely 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"

• Magnesium reacts with hot water to form an insoluble base:

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

Video "Interaction of acid oxides with water"

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 =

Remember! Only oxides of active metals react with water. Oxides of metals of intermediate activity and metals coming after hydrogen in the activity series do not dissolve in water, for example, CuO + H 2 O = reaction is not possible.

Video "Interaction of metal oxides with water"

Li + H 2 O =

Cu + H2O =

ZnO + H2O =

Al + H 2 O =

Ba + H 2 O =

K 2 O + H 2 O =

Mg + H2O =

N 2 O 5 + H 2 O =