h2o value. Chemical and physical properties of water. Anomalous properties of water

Chemistry studies the composition of water, the elements that make up water. Chemists study how water reacts with different substances, so the reaction occurs and what is formed as a result.

Water is very active in chemically substance.

Chemical properties of water:

1) Water reacts with many metals with the release of hydrogen:

2Na + 2H 2 O = H 2 + 2NaOH (boisterous)

2K + 2H 2 O = H 2 + 2KOH (boisterous)

3Fe + 4H 2 O = 4H 2 + Fe 3 O 4 (only when heated)

Not everything, just enough active metals can participate in redox reactions of this type. Alkali and alkaline earth metals of groups I and II react most easily.

From non-metals For example, carbon and its hydrogen connection(methane). These substances are much less active than metals, but are still capable of reacting with water at high temperatures:

C + H 2 O = H 2 + CO (high heat)

CH 4 + 2H 2 O = 4H 2 + CO 2 (with high heat)

2) Water decomposes into hydrogen and oxygen when exposed to electric current . This is also a redox reaction, where water is both an oxidizing agent and a reducing agent:

3) Water reacts with many oxides non-metals. Unlike the previous ones, these reactions are not redox, but coupling reactions:

4) Some metal oxides compounds can also react with water. We have already seen examples of such reactions:

Not all metal oxides are capable of reacting with water. Some of them are practically insoluble in water and therefore do not react with water. Such oxides are ZnO, TiO 2, Cr 2 O 3, from which, for example, water-resistant paints are prepared. Iron oxides are also insoluble in water and do not react with it.

5) Water forms numerous compounds in which its molecule is completely preserved. These are the so-called hydrates. If the hydrate is crystalline, then it is called crystalline hydrate. For example:

Here are other examples of hydrate formation:

H2SO4 + H2O = H2SO4 . H 2 O (sulfuric acid hydrate)

NaOH + H2O = NaOH . H 2 O (caustic soda hydrate)

Compounds that bind water into hydrates and crystalline hydrates are used as desiccants. With their help, for example, water vapor is removed from humid atmospheric air.

6) A special reaction of water is the synthesis by plants of starch (C 6 H 10 O 5) n and other similar compounds (carbohydrates), which occurs with the release of oxygen:

6n CO 2 + 5n H 2 O = (C 6 H 10 O 5) n + 6n O 2 (under light)

Water is a unique substance, the basis of all living organisms on the planet. She can acquire different shape and be in three states. What are the basic physical and chemical properties water? It's about them we'll talk in our article.

Water is...

Water is the most common thing on our planet inorganic compound. The physical and chemical properties of water are determined by the composition of its molecules.

Thus, the structure of a water molecule contains two hydrogen atoms (H) and one oxygen atom (O). Under normal environmental conditions, it is a tasteless, odorless and colorless liquid. Water can also exist in other states: in the form of steam or in the form of ice.

More than 70% of our planet is covered with water. Moreover, about 97% occurs in the seas and oceans, so most of it is not suitable for human consumption. About what are the basic chemical properties drinking water- you will find out further.

Water in nature and human life

Water is an essential component of any living organism. In particular, human body, as you know, more than 70% consists of water. Moreover, scientists suggest that it was in this environment that life on Earth originated.

Water is found (in the form of water vapor or droplets) in different layers of the atmosphere. It reaches the earth's surface from the atmosphere in the form of rain or other precipitation (snow, dew, hail, frost) through condensation processes.

Water is an object of research for a number of scientific disciplines. Among them are hydrology, hydrography, hydrogeology, limnology, glaciology, oceanology and others. All these sciences, one way or another, study the physical as well as chemical properties of water.

Water is actively used by humans in their economic activities, in particular:

• for growing crops;
• in industry (as a solvent);
• in energy (as a coolant);
• for extinguishing fires;
• in cooking;
• in pharmacy and so on.

Of course, in order to effectively use this substance in economic activity, the chemical properties of water should be studied in detail.

Types of water

As mentioned above, water in nature can be in three states: liquid (actually water), solid (ice crystals) and gaseous (steam). It can also take on any form.

There are several types of water. So, depending on the content of Ca and Na cations, water can be:

• hard;
• soft.

• fresh;
• mineral;
• salty.

In esotericism and some religions there is water:

• dead;
• alive;
• holy.

In chemistry there are also such concepts as distilled and deionized water.

Formula of water and its biological significance

Hydrogen oxide is what chemists call this substance. The formula of water is: H 2 O. It means that this compound consists of one oxygen atom and two hydrogen atoms.

The unique chemical properties of water have determined its exceptional role for the life of living organisms. It is thanks to water biological life exists on our planet.

The most unique feature of water is that it perfectly dissolves a huge number of other substances (both organic and inorganic). An important consequence of this feature is that all chemical reactions in living organisms occur quite quickly.

In addition, thanks to unique properties water, it resides precisely in liquid state, over an extremely wide temperature range.

Physical properties of water

Thanks to unique hydrogen bonds, water, under standard environmental conditions, is in a liquid state. This explains the extremely high boiling point of water. If the molecules of the substance were not connected by these hydrogen bonds, then water would boil at +80 degrees and freeze at -100 degrees.

Water boils at +100 degrees Celsius and freezes at zero degrees. True, under certain, specific conditions, it can begin to freeze even at positive temperatures. When water freezes, it increases in volume (due to a decrease in density). By the way, this is almost the only substance in nature that has such a physical property. Besides water, the only things that expand when frozen are bismuth, antimony, germanium and gallium.

The substance is also characterized by high viscosity, as well as fairly strong surface tension. Water is an excellent solvent for polar substances. You should also know that water conducts electricity very well. This feature is explained by the fact that water almost always contains large number ions of salts dissolved in it.

Chemical properties of water (grade 8)

Water molecules have extremely high polarity. Therefore, this substance in reality consists not only of simple molecules type H 2 O, but also from complex aggregates (formula - (H 2 O) n).

Chemically, water is very active; it reacts with many other substances, even when normal temperatures. When interacting with oxides of alkali and alkaline earth metals, it forms bases.

Water is also capable of dissolving a wide range of chemicals- salts, acids, bases, some gases. For this property it is often called a universal solvent. All substances, depending on whether they dissolve in water or not, are usually divided into two groups:

• hydrophilic (dissolves well in water) - salts, acids, oxygen, carbon dioxide, etc.;
• hydrophobic (poorly soluble in water) - fats and oils.

Water also enters into chemical reactions with some metals (for example, sodium), and also takes part in the process of photosynthesis in plants.

In conclusion...

Water is the most common inorganic substance on our planet. It is found almost everywhere: on earth's surface and in its depths, in the mantle and in rocks, in high layers atmosphere and even in space.

The chemical properties of water are determined by its chemical composition. It belongs to the group chemically active substances. Water interacts with many substances

, gypsum, etc.), present in the soil, is required. component of all living organisms.

Isotopic composition. There are 9 stable isotope species of water. Their average content in fresh water is as follows (mol %): 1 H 2 16 O - 99.13; 1 H 2 18 O - 0.2; 1 N 2 17 0-0.04; 1 H 2 O 16 O-0.03; the remaining five isotopic species are present in water in negligible quantities. In addition to stable isotopic species, water contains a small amount of radioactive 3 H 2 (or T 2 O). Isotopic composition of natural water of various origins. varies. The ratio 1 H/2 H is especially variable: in fresh waters- on average 6900, in sea ​​water-5500, in ice - 5500-9000. According to physical The properties of D 2 O are noticeably different from ordinary water (see Heavy water). Water containing 18 O is closer to water with 16 O.

Phys. the properties of water are abnormal. Ice melting at atm. pressure is accompanied by a decrease in volume by 9%. Temperature coef. volumetric expansion of ice and liquid water is negative at t-pax resp. below -210°C and 3.98°C. The heat capacity C° during melting almost doubles and in the range 0-100°C is almost independent of temperature (there is a minimum at 35°C). Minimum isothermal compressibility (44.9 * 10 -11 Pa -1), observed at 46°C, is expressed quite clearly. At low pressures and temperatures up to 30 °C, the viscosity of water decreases with increasing pressure. High dielectric The permeability and dipole moment of water determine its good dissolving ability in relation to polar and ionic substances. Due to high C° values, water is an important climate regulator. conditions on the earth, stabilizing the t-ru on its surface. Moreover, proximity angle N-O-N to tetrahedral (109° 28") determines the looseness of the structures of ice and liquid water and, as a consequence, the anomalous dependence of density on temperature. Therefore, large bodies of water do not freeze to the bottom, which makes it possible for life to exist in them.

Table 1 - PROPERTIES OF WATER AND WATER STEAM IN EQUILIBRIUM

But the density of modifications II-VI is significantly lower than what ice could have if the molecules were densely packed. Only in modifications VII and VIII is sufficient high density packings: in their structure, two regular networks built from tetrahedra (similar to those existing in cubic low-temperature ice Ic, isostructural to diamond), are inserted into one another; in this case, the system of straight hydrogen bonds is preserved, and the coordination. the number for oxygen doubles and reaches 8. The arrangement of oxygen atoms in ices VII and VIII is similar to the arrangement of atoms in iron and many other metals. In ordinary (Ih) and cubic (Ic) ice, as well as in ices HI, V-VII, the orientation of the molecules is not determined: both protons closest to the O atom form covalent bonds with it, which can be directed towards any two of the four neighboring oxygen atoms at the vertices of the tetrahedron. Dielectric the permeability of these modifications is high (higher than that of liquid water). Modifications II, VIII and IX are orientationally ordered; their dielectric permeability is low (approx. 3). Ice VIII is a proton-ordered version of ice VII, and ice IX is a variant of ice III. The densities of orientationally ordered modifications (VIII, IX) are close to the densities of the corresponding disordered modifications (VII, III).

Water as a solvent. Water dissolves many well. polar and dissociating into ions. Typically, pH increases with increasing temperature, but sometimes the temperature dependence is more complex. So, r-reality is plural. sulfates, carbonates and phosphates, when the temperature rises, it decreases or first increases, and then passes through a maximum. The pH value of low-polar substances (including gases that make up the atmosphere) in water is low and when the temperature rises, it usually first decreases and then passes through a minimum. As the pressure increases, the pH of gases increases, passing through a maximum at high pressures. Many substances, when dissolved in water, react with it. For example, NH 3 solutions may contain NH 4 ions (see also Hydrolysis). Between ions, atoms, and molecules dissolved in water that do not interact with it chemically. districts, and

DEFINITION

Water (hydrogen oxide)– binary inorganic compound.

Chemical formula: H2O

Structural formula:

Molar mass: 18.01528 g/mol.

Alternative names: oxide, hydrogen hydroxide, hydroxyl acid, dihydrogen monoxide, oxidane, dihydromonoxide.

In a water molecule, the oxygen atom is in a state of sp 3 hybridization, since not only valence electrons, but also lone electron pairs participate in the formation of hybrid orbitals. Hybrid orbitals are directed towards the vertices of the tetrahedron:

Due to the large difference in the electronegativity of oxygen and hydrogen, the bonds in the molecule are highly polarized, and the electron is shifted towards . A water molecule has a large dipole moment because polar bonds located asymmetrically.

The strong polarization of the O–H bond is associated with the formation of hydrogen bonds between water molecules. Each water molecule can form up to four hydrogen bonds - two of them are formed by an oxygen atom, and two more by hydrogen atoms:

The formation of hydrogen bonds determines more high temperature boiling point, viscosity and surface tension of water compared to hydride analogues (selenium and tellurium).

Isotopic modifications of water

Depending on the type of hydrogen isotopes included in the molecule, the following are distinguished: isotopic modifications of water:

Considering that oxygen has three stable isotope(16 O, 17 O and 18 O), you can create 18 formulas for water molecules that differ in isotopic composition. Typically, natural water contains all of these types of molecules.

Examples of solving problems on the topic “water formula”

EXAMPLE 1

Exercise	9 liters of water were poured into the car radiator and 2 liters of methyl with a density of 0.8 g/ml were added. At what minimum temperature can you now leave the car? outdoors without fear that the water in the radiator will freeze (the cryoscopic constant of water is 1.86 K kg/mol)?
Solution	According to Raoult's law, the decrease in the crystallization temperature of dilute solutions of nonelectrolytes is equal to: where: – decrease in the freezing temperature of the solution; К cr – cryoscopic constant of the solvent; Cm is the molal concentration of the solution; m B is the mass of the dissolved substance; m A is the mass of the solvent; M B – molar mass of the solute. The mass of methyl alcohol is: The mass of water is equal to: The molar mass of methyl alcohol is 32 g/mol Let's calculate the change in freezing temperature:
Answer	The car can be left outside at temperatures above –10.3°C

EXAMPLE 2

Exercise	How many grams of Na 2 SO 4 10H 2 O should be dissolved in 250 g of water to obtain a solution containing 5% anhydrous?
Solution	The molar mass of Na 2 SO 4 is: Molar mass of crystalline hydrate: Let us denote the amount (mol) of dissolved salt as x. Then the solution will be equal to: The mass of anhydrous salt in the finished solution will be equal to:

DEFINITION

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

Formula – H 2 O. Molar mass – 18 g/mol. 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 some 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 a reaction (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 value specific heat capacity among all substances in liquid and solid states of aggregation. Specific heat water melting – 333.25 kJ/kg (0 C), vaporization – 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 definition mass fraction substances 20% acetic acid solution represents 80 ml of solvent (water) 20 g of acid, and 5% acetic acid solution represents 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	Upon combustion organic matter weighing 4.8 g, 3.36 liters were formed carbon dioxide(n.s.) and 5.4 g of water. 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 chemical elements DI. 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: 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 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 organic matter derived from combustion products and using hydrogen density differ, then the ratio 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.