Reflections (not educational material!!!) on the topic

properties of the water molecule

The most common substance on our planet. Without her, there would be no life. All living structures, with the exception of viruses, are mostly water. On her example, children at school explain the structure of molecules, chemical formulas. Properties that are characteristic only of water are used in wildlife, as well as in the economic life of a person.

Since childhood, we have known a substance that has never raised any questions. Well water, so what? And in such a simple, it would seem, substance, many mysteries are hidden.

Water is the main natural solvent. All reactions in living organisms take place in one way or another. aquatic environment substances react in solution.

Water has an excellent heat capacity, but a rather low thermal conductivity. This allows the use of water as a heat transport. The cooling mechanism of many organisms is based on this principle. And in nuclear energy, water, due to this property, is used as a coolant.

In water, not only reactions take place, it itself enters into reactions. Hydration, photolysis, etc.

These are just some of the properties, no substance can boast of such a set of properties. Truly this substance is unique.

Well, now closer to the topic.

Always, everywhere, even at school in chemistry lessons, it is simply called “water”.

But what chemical naming and properties of the water molecule?

On the Internet and educational literature, you can find such names: hydrogen oxide, hydrogen hydroxide, hydroxyl acid. These are the most common ones.

So what class is not organic matter refers to water?

Let's look into this issue.

Below is the diagram:

This version is more plausible: the hydroxyl group clearly hints at something similar. But what hydroxide? Let's look again at the properties of hydroxides:

Properties of basic hydroxides (bases):

For soluble bases (alkalis):

Soluble bases (alkalis) are characterized by ion exchange reactions.

Interaction of soluble bases (alkalis) with acidic bases.

Interaction with amphoteric hydroxides.

Insoluble bases decompose when heated.

The water molecule does not exhibit a single property, except that, with strong heating, it will undergo decomposition, but this is the case with all substances - there is a certain temperature threshold, above which bonds can no longer exist and are destroyed.

There is also an argument “against” amphoteric and basic hydroxide - basic and amphoteric hydroxides form only metals.

Now we come to the most interesting part. It turns out that water is

acid hydroxide, that is oxygenated acid.

Let's look at the properties.

Acid hydroxides are characterized by:

Reactions with metals.

Reactions with basic and amphoteric oxides.

Reactions with bases and amphoteric hydroxides.

Reactions with salts.

For strong acids as well as ion exchange reactions.

Displacement of weaker, as well as volatile acids from salts.

Almost all of these properties are characteristic of the water molecule.

Let's analyze in detail.

• Reactions with metals. Not all metals are able to react with water. Water as an acid is very weak, but, nevertheless, it exhibits this property:

HOH + Na → NaOH + H 2 - hydrogen is displaced from water - water behaves like most acids.

• Reactions with basic and amphoteric oxides. It does not react with amphoteric oxides, since the acidic properties are weak, but it reacts with basic oxides (not with all, though, this is due to weak acidic properties):

HOH + Na 2 O → 2NaOH

• Reactions with bases and amphoteric hydroxides. Here, water cannot boast of such reactions - because of its weakness as acids.
• Reactions with salts. Some salts undergo hydrolysis - just the same reaction with water.

This reaction also illustrates the last property - the displacement of acid, water turns out to displace hydrogen sulfide.

From the definition: " acid is a complex substance consisting of hydrogen and an acid residue, when dissociating into an H + cation and an acid residue cation«.

Everything fits. And it turns out that the acid residue is the hydroxyl group OH.

And, as I said before, water forms salts, it turns out that water-acid salts are basic and amphoteric hydroxides: a metal combined with an acidic residue (OH).

And reaction schemes:

acid + metal → salt + hydrogen (generally)

HOH + Na → NaOH + H2

acid + basic oxide → salt water

HOH + Na 2 O → 2NaOH (salt is formed, only water is not formed, and why would it suddenly result from a reaction with water, water should form)

salt + acid → another acid + another salt

Al 2 S 3 + HOH → Al(OH) 3 ↓ + H 2 S

So, we came to the conclusion that amphoteric and basic hydroxides are salts of water - acids.

Then what are they called?

The whole term "hydroxide" is also applicable to oxygen-containing acids. According to the rules it turns out:

ion name + at = Hydrox + at.

Water salts are hydroxates.

Water is such a weak acid that it exhibits some amphoteric properties, such as reactions with acidic oxides.

And in water, a neutral environment, and not acidic, as in all acids - this is an exception to the rule.

But in the end, as the remarkable Russian organic chemist said, “There are no impossible reactions, and if the reaction does not take place, then the catalyst has not yet been found.”

Summarize.

Let's formulate the main provisions theory "Water - acid":

The water molecule is a weak (very weak) acid.

Water is so weak that it exhibits amphoteric properties and has a neutral reaction of the medium.

Water as an acid forms salts - hydroxates.

Hydroxates include amphoteric and basic hydroxides.

Water formula: HOH.

The correct names for water are: hydrogen hydroxide, hydroxyl acid.

The formulas for covalent bonds are fundamentally different from the formulas for ionic bonds. The fact is that covalent compounds can be formed by the most different ways, therefore, as a result of the reaction, the appearance of various compounds is possible.

1. Empirical formula

The empirical formula indicates the elements that make up the molecule, with the smallest integer ratios.

For example, C 2 H 6 O - the compound contains two carbon atoms, six hydrogen atoms and one oxygen atom.

2. Molecular formula

The molecular formula indicates what atoms the compound consists of and in what quantities these atoms are in it.

For example, for the compound C 2 H 6 O molecular formulas can be: C 4 H 12 O 2 ; C 6 H 18 O 3 ...

For a complete description of a covalent compound, the molecular formula is not enough:

As you can see, both connections have the same molecular formula- C 2 H 6 O, but they are completely different substances:

• dimethyl ether is used in refrigeration;
• ethyl alcohol is the basis of alcoholic beverages.

3. Structural formula

The structural formula serves to accurately determine the covalent compound, because, in addition to the elements in the compound and the number of atoms, it also shows link diagram connections.

The structural formula is electron point formula And Lewis formula.

4. Structural formula for water (H 2 O)

Consider the procedure for constructing a structural formula using the example of a water molecule.

I We build the connection frame

The atoms of the compound are arranged around the central atom. As the central atoms usually act: carbon, silicon, nitrogen, phosphorus, oxygen, sulfur.

II Find the sum of valence electrons of all atoms of the compound

For water: H 2 O \u003d (2 1 + 6) \u003d 8

There is one valence electron in the hydrogen atom, and 6 in the oxygen atom. Since there are two hydrogen atoms in the compound, then total number valence electrons of a water molecule will be equal to 8.

III Determine the number of covalent bonds in a water molecule

We determine by the formula: S=N-A, Where

S is the number of electrons shared in the molecule;

N- the sum of valence electrons corresponding to the completed external energy level of atoms in the compound:

N=2- for the hydrogen atom;

N = 8- for atoms of other elements

A is the sum of the valence electrons of all atoms in the compound.

N = 2 2 + 8 = 12

A = 2 1 +6 = 8

S=12 - 8=4

There are 4 shared electrons in a water molecule. Since a covalent bond consists of a pair of electrons, we get two covalent bonds.

IV We distribute joint electrons

There must be at least one bond between the central atom and the atoms that surround it. For a water molecule, there will be two such bonds for each hydrogen atom:

V Distribute the remaining electrons

Of the eight valence electrons, four have already been distributed. Where to "put" the remaining four electrons?

Each atom in a compound must have a full octet of electrons. For hydrogen, these are two electrons; for oxygen - 8.

The shared electrons are called binding.

The electron point formula and the Lewis formula clearly describe the structure of a covalent bond, but they are cumbersome and take up a lot of space. These shortcomings can be avoided by using compressed structural formula , which indicates only the order of "following" links.

An example of a compressed structural formula:

• dimethyl ether - CH 3 OCH 3
• ethyl alcohol - C 2 H 5 OH

Everyone should know the properties of water - since they largely determine our life and ourselves as such ...

Chemical and physical properties of water in a liquid state - terms, definitions and comments

Strictly speaking, in this article we will briefly consider not onlychemical and physical properties liquid water,but also the properties inherent in it in general as such.

You can read more about the properties of water in the solid state in our article - PROPERTIES OF WATER IN SOLID STATE(read →).

Water- a super-significant substance for our planet. Without it, life on Earth is impossible; not a single geological process takes place without it. The great scientist and thinker Vladimir Ivanovich Vernadsky wrote in his works that there is no such component, the value of which could "compare with it in terms of its influence on the course of the main, most formidable geological processes." Water is present not only in the body of all living creatures on our planet, but also in all substances on Earth - in minerals, in rocks ... The study of the unique properties of water constantly reveals more and more secrets to us, sets us new mysteries and throws new challenges.

Anomalous properties of water

Many physical and chemical properties of water surprise and fall out of the general rules and patterns and are abnormal, for example:

• In accordance with the laws established by the principle of similarity, within the framework of such sciences as chemistry and physics, we might expect that:
  • water will boil at minus 70°С, and freeze at minus 90°С;
  • water it will not drip from the tip of the tap, but pour in a thin stream;
  • ice will sink rather than float on the surface;
  • in glass water more than a few grains of sugar would not dissolve.
• Surface water has a negative electrical potential;
• When heated from 0°C to 4°C (3.98°C to be exact), water contracts;
• The surprisingly high heat capacity of water liquid state;

As noted above, in this material we list the main physical and chemical properties of water and make brief comments on some of them.

Physical properties of water

PHYSICAL PROPERTIES are properties that appear outside of chemical reactions.

Purity

The purity of water depends on the presence of impurities, bacteria, salts in it. heavy metals… , to get acquainted with the interpretation of the term CLEAN WATER according to our website, you need to read the article PURE WATER (read →) .

Color

Color water– depends on the chemical composition and mechanical impurities

For example, let's take the definition of "Colors of the Sea", given by the "Great Soviet Encyclopedia".

The color of the sea. The color perceived by the eye when the observer looks at the surface of the sea. The color of the sea depends on the color of sea water, the color of the sky, the number and nature of clouds, the height of the Sun above the horizon, and other reasons.

The concept of the color of the sea should be distinguished from the concept of the color of sea water. The color of sea water is understood as the color perceived by the eye when viewing sea water vertically over a white background. Only an insignificant part of the light rays incident on it is reflected from the sea surface, the rest of them penetrate deep into, where they are absorbed and scattered by water molecules, particles of suspended matter and the smallest gas bubbles. The scattered rays reflected and emerging from the sea create the C. m. Water molecules scatter blue and blue most of all. green rays. Suspended particles scatter all rays almost equally. That's why sea ​​water with a small amount of suspension it seems blue-green (the color of the open parts of the oceans), and with a significant amount of suspension it is yellowish-green (for example, Baltic). The theoretical side of the doctrine of the C. m. was developed by V. V. Shuleikin and C. V. Raman.

Great Soviet Encyclopedia. - M.: Soviet Encyclopedia. 1969-1978

Smell

Smell water– Pure water is usually odorless.

Transparency

Transparency water- depends on the mineral substances dissolved in it and the content of mechanical impurities, organic substances and colloids:

TRANSPARENCY OF WATER - the ability of water to transmit light. Usually measured by the Secchi disk. It depends mainly on the concentration of organic and inorganic substances suspended and dissolved in water. It can sharply decrease as a result of anthropogenic pollution and eutrophication of water bodies.

Ecological encyclopedic dictionary. - Chisinau I.I. Grandpa. 1989

TRANSPARENCY OF WATER - the ability of water to transmit light rays. It depends on the thickness of the water layer passed by the rays, the presence of suspended impurities, dissolved substances, etc. In water, red and yellow rays are absorbed more strongly, violet rays penetrate deeper. According to the degree of transparency, in order of decreasing it, waters are distinguished:

• transparent;
• slightly opalescent;
• opalescent;
• slightly cloudy;
• cloudy;
• very cloudy.

Dictionary of hydrogeology and engineering geology. - M.: Gostoptekhizdat. 1961

Taste

The taste of water depends on the composition of the substances dissolved in it.

Dictionary of hydrogeology and engineering geology

The taste of water is a property of water that depends on the salts and gases dissolved in it. There are tables of palpable concentration of salts dissolved in water (in mg / l), for example, the following table (according to Staff).

Temperature

Melting point of water:

MELTING POINT - The temperature at which a substance changes from solid to liquid. The melting point of a solid is equal to the freezing point of a liquid, for example, the melting point of ice, 0°C, is equal to the freezing point of water.

Boiling point of water : 99.974°C

Scientific and technical encyclopedic dictionary

BOILING POINT, the temperature at which a substance passes from one state (phase) to another, i.e. from liquid to vapor or gas. The boiling point increases as the external pressure increases and decreases as it decreases. It is usually measured at a standard pressure of 1 atmosphere (760 mm Hg). The boiling point of water at a standard pressure is 100 °C.

Scientific and technical encyclopedic dictionary.

Triple point of water

Triple point of water: 0.01 °C, 611.73 Pa;

Scientific and technical encyclopedic dictionary

TRIPLE POINT, temperature and pressure at which all three states of matter (solid, liquid, gaseous) can exist simultaneously. For water, the triple point is at a temperature of 273.16 K and a pressure of 610 Pa.

Scientific and technical encyclopedic dictionary.

Surface tension of water

Surface tension of water - determines the strength of the adhesion of water molecules to each other, for example, how this or that water is absorbed by the human body depends on this parameter.

Adhesion and cohesion of water

Adhesion and cohesion are properties that determine the "stickiness of water" to other materials. Adhesion determines the "stickiness" of water to other substances, and cohesion is the stickiness of water molecules in relation to each other.

Capillarity

Capillarity is the property of water that allows water to rise vertically in porous materials. This property is realized through other properties of water, such as surface tension, adhesion and cohesion.

Hardness of water

Water hardness - determined by the amount of salt content, read more in the materials HARD WATER - WHAT IS IT (read →) And WATER MINERALIZATION (read →).

Marine vocabulary

WATER HARDNESS (Stiffness of Water) - a property of water, bled by the content of alkaline earth metal salts dissolved in it, ch. arr. calcium and magnesium (in the form of bicarbonate salts - bicarbonates), and salts of strong mineral acids - sulfuric and hydrochloric. The hardness of water is measured in special units, the so-called. degrees of hardness. The degree of hardness is the weight content of calcium oxide (CaO), equal to 0.01 g in 1 liter of water. Hard water is unsuitable for feeding boilers, as it contributes to the strong formation of scale on their walls, which can cause burnout of the boiler tubes. Boilers of large capacities and especially high pressures must be fed with completely purified water (condensate from steam engines and turbines, purified by filters from oil impurities, as well as distillate prepared in special evaporator apparatuses).

Samoilov K.I. Marine Dictionary. - M.-L.: State Naval Publishing House of the NKVMF of the USSR, 1941

Scientific and technical encyclopedic dictionary

HARDNESS OF WATER, the inability of water to form foam with soap due to salts dissolved in it, mainly calcium and magnesium.

Scale in boilers and pipes is formed due to the presence of dissolved calcium carbonate in water, which enters the water upon contact with limestone. In hot or boiling water, calcium carbonate precipitates as hard lime deposits on surfaces inside boilers. Calcium carbonate also prevents soap from lathering. The ion-exchange container (3) is filled with granules coated with sodium-containing materials. with which the water comes into contact. Sodium ions, being more active, replace calcium ions. Since sodium salts remain soluble even when boiled, scale does not form.

Scientific and technical encyclopedic dictionary.

Water structure

under the structure water refers to a certain arrangement of water molecules in relation to each other. This concept is actively used in the theory of structured water- read our article STRUCTURED WATER - BASIC CONCEPTS (read →).

Water mineralization

Mineralization water:

Ecological Encyclopedic Dictionary

MINERALIZATION OF WATER - saturation of water inorganic. (mineral) substances present in it in the form of ions and colloids; the total amount of inorganic salts contained mainly in fresh water, the degree of mineralization is usually expressed in mg / l or g / l (sometimes in g / kg).

Ecological encyclopedic dictionary. - Chisinau: Main edition of the Moldavian Soviet Encyclopedia. I.I. Grandpa. 1989

Viscosity of water

Viscosity of water characterizes the internal resistance of liquid particles to its movement:

Geological dictionary

The viscosity of water (liquid) is a property of a liquid that causes the appearance of a friction force during movement. It is a factor that transfers motion from layers of water moving at a high speed to layers with a lower speed. The viscosity of water depends on the temperature and concentration of the solution. Physically, it is estimated by the coefficient. viscosity, which is included in a number of formulas for the movement of water.

Geological dictionary: in 2 volumes. - M.: Nedra. Edited by K. N. Paffengolts et al. 1978

There are two types of viscosity water:

• The dynamic viscosity of water is 0.00101 Pa s (at 20°C).
• The kinematic viscosity of water is 0.01012 cm2/s (at 20°C).

Critical point of water

critical point water called its state at a certain ratio of pressure and temperature, when its properties are the same in the gaseous and liquid state (gaseous and liquid phase).

Critical point of water: 374°C, 22.064 MPa.

The dielectric constant

Dielectric constant, in general, is a coefficient showing how much the force of interaction between two charges in a vacuum is greater than in a certain medium.

In the case of water, this figure is unusually high and for static electric fields is 81.

Heat capacity of water

Heat capacity water- water has a surprisingly high heat capacity:

Ecological dictionary

Heat capacity is the property of substances to absorb heat. It is expressed as the amount of heat absorbed by a substance when it is heated by 1°C. The heat capacity of water is about 1 cal/g, or 4.2 J/g. The heat capacity of the soil (at 14.5-15.5°C) ranges (from sandy to peaty soils) from 0.5 to 0.6 cal (or 2.1-2.5 J) per unit volume and from 0.2 up to 0.5 cal (or 0.8-2.1 J) per unit mass (g).

Ecological dictionary. - Alma-Ata: "Science". B.A. Bykov. 1983

Scientific and technical encyclopedic dictionary

SPECIFIC HEAT CAPACITY (symbol c), the heat required to raise the temperature of 1 kg of a substance by 1K. It is measured in J / K.kg (where J is JOUL). Substances with high specific heat, such as water, require more energy to raise the temperature than substances with low specific heat.

Scientific and technical encyclopedic dictionary.

Thermal conductivity of water

The thermal conductivity of a substance refers to its ability to conduct heat from its hotter parts to its colder parts.

Heat transfer in water occurs either at the molecular level, that is, it is transferred by molecules water, or due to the movement / movement of any volumes of water - turbulent thermal conductivity.

The thermal conductivity of water depends on temperature and pressure.

Fluidity

The fluidity of substances is understood as their ability to change their shape under the influence of constant stress or constant pressure.

The fluidity of liquids is also determined by the mobility of their particles, which at rest are unable to perceive shear stresses.

Inductance

Inductance determines magnetic properties closed circuits of electric current. Water, with the exception of some cases, conducts electric current, and therefore has a certain inductance.

Density of water

Density water- is determined by the ratio of its mass to volume at a certain temperature. Read more in our material - WHAT IS THE DENSITY OF WATER (read →) .

Water compressibility

Water compressibility– is very small and depends on the salinity of the water and pressure. For example, for distilled water, it is 0.0000490. In natural natural conditions water is practically incompressible, but in industrial production for technical purposes, water is highly compressed. For example, for cutting hard materials, including such as metals.

Electrical conductivity of water

The electrical conductivity of water depends largely on the amount of salts dissolved in them.

Radioactivity

Water radioactivity- depends on the content of radon in it, the emanation of radium.

Physical and chemical properties of water

Dictionary of hydrogeology and engineering geology

PHYSICAL AND CHEMICAL PROPERTIES OF WATER — parameters that determine the physical and chemical characteristics of natural waters. These include indicators of hydrogen ion concentration (pH) and redox potential (Eh).

Dictionary of hydrogeology and engineering geology. - M.: Gostoptekhizdat. Compiled by: A. A. Makkaveev, editor O. K. Lange. 1961

Solubility

Different sources classify this property in different ways - some refer it to the physical, others to the chemical properties of the substance. Therefore, on this stage we took it to physical and chemical properties water, which is confirmed by one of the definitions of solubility given below.

Big Encyclopedic Dictionary

SOLUBILITY - the ability of a substance in a mixture with one or more other substances to form solutions. A measure of the solubility of a substance in a given solvent is the concentration of its saturated solution at a given temperature and pressure. The solubility of gases depends on temperature and pressure, the solubility of liquid and solids virtually independent of pressure.

Big encyclopedic Dictionary. 2000

Directory of road terms

Solubility is the property of a material (substances) to form homogeneous systems having the same chemical composition and physical properties.

Directory of road terms, M. 2005

general chemistry

Solubility - the property of gaseous, liquid and solid substances to go into a dissolved state; expressed by the equilibrium mass ratio of solute and solvent at a given temperature.

General chemistry: A. V. Zholnin textbook; ed. V. A. Popkova, A. V. Zholnina. 2012

Physical Encyclopedia

Solubility - the ability of a substance to form solutions with other substances. It is quantitatively characterized by the concentration of a substance in a saturated solution. Solubility is determined by physical. and chem. the affinity of the molecules of the solvent and the solute, a cut is characterized by the so-called. energy of interchange of solution molecules. As a rule, solubility is high if the molecules of the solute and the solvent have similar properties ("like dissolves like").

The dependence of solubility on temperature and pressure is established using the Le Chatelier-Brown principle. Solubility increases with increasing pressure and passes through a maximum at high pressures; The solubility of gases in liquids decreases with increasing temperature, while in metals it increases.

Physical encyclopedia. In 5 volumes. - M.: Soviet Encyclopedia. Chief Editor A. M. Prokhorov. 1988

Acid-base balance (pH of water)

The acid-base balance of water is determined by the pH indicator, the value of which can vary from 0 to 14. A value of 7 - defines the acid-base balance of water as neutral, if less than 7 - acidic water, more than 7 - alkaline water.

Redox potential of water

The redox potential of water (ORP) is the ability of water to enter into biochemical reactions.

Chemical properties of water

CHEMICAL PROPERTIES OF A SUBSTANCE are properties that appear as a result of chemical reactions.

Below are Chemical properties water according to the textbook “Fundamentals of Chemistry. Internet textbook" by A. V. Manuylov, V. I. Rodionov.

Interaction of water with metals

When water interacts with most metals, a reaction occurs with the release of hydrogen:

• 2Na + 2H2O = H2 + 2NaOH (violently);
• 2K + 2H2O = H2 + 2KOH (violently);
• 3Fe + 4H2O = 4H2 + Fe3O4 (only when heated).

Not all, but only sufficiently active metals can participate in redox reactions of this type. Most readily react alkaline and alkaline earth metals I and II groups.

When water interacts with noble metals such as gold, platinum..., there is no reaction.

Interaction water with non-metals

Of non-metals, for example, carbon and its hydrogen bond(methane). These substances are much less active than metals, but still able to react with water at high temperatures:

• C + H2O = H2 + CO (with strong heating);
• CH4 + 2H2O = 4H2 + CO2 (with strong heating).

Interaction water with electric current

When exposed electric shock water decomposes into hydrogen and oxygen. It is also a redox reaction, where water is both an oxidizing agent and a reducing agent.

Interaction of water with non-metal oxides

Water reacts with many non-metal oxides and some metal oxides. These are not redox reactions, but compound reactions:

• SO2 + H2O = H2SO3 (sulphurous acid);
• SO3 + H2O = H2SO4 (sulfuric acid);
• CO2 + H2O = H2CO3 (carbonic acid).

Interaction of water with metal oxides

Some metal oxides can also react with water.

We have already seen examples of such reactions:

CaO + H2O = Ca(OH)2 (calcium hydroxide (slaked lime).

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. For example: ZnO, TiO2, Cr2O3, from which, for example, water-resistant paints are prepared. Iron oxides are also insoluble in water and do not react with it.

Hydrates and crystalline hydrates

Water forms compounds, hydrates and crystalline hydrates, in which the water molecule is completely preserved. .

For example:

• CuSO4 + 5H2O = CuSO4.5H2O;
• CuSO4 is a white substance (anhydrous copper sulfate);
• CuSO4.5H2O - crystalline hydrate (copper sulfate), blue crystals.

Other examples of hydrate formation:

• H2SO4 + H2O = H2SO4.H2O (sulfuric acid hydrate);
• NaOH + H2O = NaOH.H2O (caustic soda hydrate).

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

Biosynthesis

Water is involved in bio-synthesis as a result of which oxygen is formed:

6n CO 2 + 5n H 2 O \u003d (C 6 H 10 O 5) n + 6n O 2 (under the action of light)

Conclusion

We see that the properties of water are diverse and cover almost all aspects of life on Earth. As one of the scientists formulated … it is necessary to study water in a complex way, and not in the context of its individual manifestations.

In preparing the material, information from books was used- Yu. P. Rassadkina “Ordinary and extraordinary water”, Yu. Ya. Fialkov “Unusual properties of ordinary solutions”, Textbook “Fundamentals of Chemistry. Internet textbook" by A. V. Manuylov, V. I. Rodionov and others.

Other names: hydrogen oxide, dihydrogen monoxide.

Water is an inorganic compound with chemical formula H2O.

Physical Properties

Chemical properties and preparation methods

Water of the highest purity

Distilled water used in laboratories usually still contains appreciable amounts of dissolved carbon dioxide, as well as traces of ammonia, organic bases, and other organic substances. Obtaining very pure water is carried out in several stages. First, 3 g of NaOH (analytical grade) and 0.5 g of KMnO 4 are added to water for every 1 liter, and distillation is carried out in thin section equipment made of Duran 50 or Solidex glass, and only the middle fraction is collected. In this way, dissolved carbon dioxide is removed and organic matter is oxidized. Removal of ammonia is achieved during the second and third distillations with the addition of 3 g KHSO 4 or 5 ml of 20% H 3 PO 4 , and these reagents are preheated with big amount KMnO 4 . To prevent the “creeping out” of the added electrolyte into the condensate, a “dry section” is created during the third distillation, for which the length of the tube between the cap on the flask and the condenser is heated to 150 °C. The last distillation, which serves to remove traces of electrolytes, is carried out from a quartz flask with a quartz condenser. The upper tube of the refrigerator, bent at a right angle, is inserted without any sealing material directly into the constriction of the flask (Fig. 1). In order to avoid water splashes, it is advisable to place a spray trap on the steam path. Flasks made of quartz, platinum, Duran 50 or Solidex glass, which are pre-treated with water vapor, serve as receivers. The water obtained in this way is "pure pure" (i.e., with a pH value of 7.00).

Rice. 1. Methods for attaching a flask to a refrigerator during the distillation of high purity water.

a - simple (cheap) execution;
b - with a spray trap. The purity of water is determined by measuring its electrical conductivity, which immediately after the distillation of water should be less than 10 -6 Ohm -1 ·cm -1 . The test for the content of carbon dioxide in water is carried out using barite water, and the test for ammonia content is carried out with Nessler's reagent. Very pure water is stored in quartz or platinum vessels. Duran 50 or Solidex glass flasks, previously steamed for a long time and designed exclusively for this purpose, can also be used for this. Such vessels are best closed with polished caps.

Water intended for electrical conductivity measurement

Method 1. Obtaining by distillation. Water required for conducting conductivity measurements the highest degree Purity is obtained by particularly thorough distillation of already previously very well purified water. The latter should have electrical conductivity at 25°С ( χ ) equal to 1 10 -6 -2 10 -6 Ohm -1 cm -1 . It is obtained by the above method or by double distillation: a) with a mixture of potassium permanganate and sulfuric acid and b) with barium hydroxide. For distillation, a Duran 50 or Solidex glass flask is used with a copper or quartz condenser attached to it.

Rice. 2. The design of the device for distillation of water, designed to measure the electrical conductivity.

1 - heating winding (60 Ohm); 2 - heating mantle (130 Ohm); 3 - adapter on thin sections.

All parts of the apparatus for single-stage distillation according to the Kortyum method (Fig. 2) are made of Duran 50 or Solidex glass, with the exception of a short quartz cooler attached to the distillation apparatus on a normal section. The bent part leading to the cooler is heated with a heating element (60 ohm) to a temperature exceeding 100°C, in order to avoid entrainment of liquid water into the cooler. The 60 cm high reflux condenser located below is equipped with a Widmer coil. The refrigerator is attached to the spare bottle with transitional thin sections. In order for the distillate to retain low electrical conductivity for a long time, transitional sections and a spare bottle must first be treated with hot dilute acid for several days. High purity water χ =(1-2)·10 -6 Ohm -1 ·cm -1) is distilled by passing through the apparatus a slow stream of compressed air from a steel cylinder at a speed of approximately 1 bubble per second. The air is pre-purified by passing it through seven wash bottles, of which one is filled with concentrated sulfuric acid, three contain a 50% potassium hydroxide solution, and three contain "water for measuring electrical conductivity" (the last three wash bottles must be equipped with porous glass plates). The resulting water is taken from the spare bottle by displacing it with purified, as indicated above, compressed air. The water in the flask is heated using a mantle heater with a power of 300 W. The flask can be easily filled with water or emptied with a vertical tube located in the middle of the flask. The easiest way to fill the flask is to stop the flow of air and turn off the heating mantle.

A vessel is connected to the three-way cock at the end of the refrigerator, in which the measurement of the electrical conductivity of the distilled water is carried out until the desired value is reached. χ . After that, the water is sent to the spare collection by switching the tap.

In this way, in 1 hour you can get 100 ml of water, for which at 25 ° C χ=2·10 -7 Ohm -1 cm -1. If the distillation is carried out very slowly, then the electrical conductivity of the resulting water can reach the value χ=10 -8 Ohm -1 ·cm -1 .

Method 2. Obtaining by ion exchange. In large quantities, "water for measuring electrical conductivity" (x from 7 10 -8 to 1.5 10 -7 Ohm -1 cm -1 can be obtained by ion exchange in the equipment shown schematically in Fig. 3.

Rice. 3. Installation design for: obtaining high purity water by ion exchange.

1 - ion exchange column;
2 - porous glass filter;
3 - cell for measuring electrical conductivity;
4 - collection;
6 - tube for absorption of carbon dioxide. A Pyrex glass column (75 cm long and 7.5 cm in diameter) with a porous glass plate at the bottom is filled with a mixture (750 g) consisting of one part Amberlite IR 120 (16-50 mesh) and two parts Amberlite IRA 400 (20-50 mesh). 50 mesh). The resin in the column is covered with a perforated polyethylene circle that floats in the solution and serves to prevent the resin from being agitated by the water flow. Normal distilled water is passed through the column. As soon as the electrical conductivity of water, measured in cell 3, reaches a sufficiently low value, it is first washed, and then vessel 4 is filled with it. The ingress of carbon dioxide from air into the water is prevented by two calcium chloride tubes 5 inserted into the column and into the receiver, filled with carbosorb" with an indicator.

Resin pre-treatment and regeneration is carried out as follows. The IR 120 cation exchanger is washed several times with distilled water, removing small particles by decantation. Then, on a glass porous filter, the resin is treated twice alternately with 1 N. NaOH and 2 n. HCl, washing after each treatment with distilled water until neutral. The anion exchanger IRA 400 is also first washed with distilled water. After decantation, the resin on a glass porous filter is treated with 2 N. NaOH, which does not contain carbonates (the water for preparing the solution is freed from carbon dioxide by distillation). Processing is carried out until the concentration of chlorine ions in the eluate is reduced to a minimum. After that, the resin is washed with distilled water until a neutral reaction in the wash water is reached.

The mixture is separated before the resin is regenerated. Resin is added to the beaker, suspended in ethanol, and chloroform is added, with the anion exchanger collecting in the top layer. The mixture is divided into component parts and separate regeneration is carried out.

When ordinary distilled water is passed through the apparatus, it is possible to obtain, without regeneration, at a rate of 1 l/min, 7000 liters of "water for measuring electrical conductivity" with x=5.52 10 -8 Ω -1 cm -1 at 25 °C.

List of used literature

1. Volkov, A.I., Zharsky, I.M. Big chemical reference book / A.I. Volkov, I.M. Zharsky. - Mn.: modern school, 2005. - 608 with ISBN 985-6751-04-7.
2. M. Bowdler, G. Brouwer, F. Huber, V. Kvasnik, P.V. Schenk, M. Schmeiser, R. Steudel. Guide to inorganic synthesis: In 6 volumes. T.1. Per. With. German / Ed. G. Brouwer. - M.: Mir, 1985. - 320 p., ill. [With. 152-156]

The well-known formula of the basis of life - water. Its molecule consists of two hydrogen atoms and one oxygen, which is written as H2O. If there is twice as much oxygen, then a completely different substance will turn out - H2O2. What is it and how will the resulting substance differ from its “relative” of water?

H2O2 - what is this substance?

Let's dwell on it in more detail. H2O2 is the formula for hydrogen peroxide, yes, the one used to treat scratches, white. Hydrogen peroxide H2O2 - scientific.

A 3% peroxide solution is used for disinfection. In pure or concentrated form, it causes chemical burns to the skin. A thirty percent peroxide solution is otherwise called perhydrol; it was previously used in hairdressing salons to bleach hair. The skin burned by him also becomes white.

Chemical properties of H2O2

Hydrogen peroxide is a colorless liquid with a "metallic" taste. It is a good solvent and is easily soluble in water, ether, alcohols.

Three and six percent peroxide solutions are usually prepared by diluting a thirty percent solution. When concentrated H2O2 is stored, the substance decomposes with the release of oxygen, so it should not be stored in tightly sealed containers in order to avoid an explosion. With a decrease in the concentration of peroxide, its stability increases. Also, to slow down the decomposition of H2O2, various substances can be added to it, for example, phosphoric or salicylic acid. To store solutions of strong concentration (more than 90 percent), sodium pyrophosphate is added to the peroxide, which stabilizes the state of the substance, and aluminum vessels are also used.

H2O2 in chemical reactions can be both an oxidizing agent and a reducing agent. More often, however, peroxide exhibits oxidizing properties. Peroxide is considered to be an acid, but a very weak one; salts of hydrogen peroxide are called peroxides.

as a method of obtaining oxygen

The decomposition reaction of H2O2 occurs when a substance is exposed to high temperature (more than 150 degrees Celsius). The result is water and oxygen.

Reaction formula - 2 H2O2 + t -> 2 H2O + O2

The oxidation state of H in H 2 O 2 and H 2 O \u003d +1.
The oxidation state of O: in H 2 O 2 \u003d -1, in H 2 O \u003d -2, in O 2 \u003d 0
2 O -1 - 2e -> O2 0

O -1 + e -> O -2
2 H2O2 = 2 H2O + O2

Decomposition of hydrogen peroxide can also occur at room temperature if a catalyst is used ( Chemical substance speeding up the reaction).

In laboratories, one of the methods for obtaining oxygen, along with the decomposition of berthollet salt or potassium permanganate, is the reaction of peroxide decomposition. In this case, manganese (IV) oxide is used as a catalyst. Other substances that accelerate the decomposition of H2O2 are copper, platinum, sodium hydroxide.

The history of the discovery of peroxide

The first steps towards the discovery of peroxide were made in 1790 by the German Alexander Humboldt, when he discovered the transformation of barium oxide into peroxide when heated. That process was accompanied by the absorption of oxygen from the air. Twelve years later, scientists Tenard and Gay-Lussac conducted an experiment on burning alkali metals with excess oxygen, resulting in sodium peroxide. But hydrogen peroxide was obtained later, only in 1818, when Louis Tenard studied the effect of acids on metals; for their stable interaction, a low amount of oxygen was needed. Conducting a confirmatory experiment with barium peroxide and sulfuric acid, the scientist added water, hydrogen chloride and ice to them. After a short time, Tenar found small solidified drops on the walls of the container with barium peroxide. It became clear that it was H2O2. Then they gave the resulting H2O2 the name "oxidized water". This was hydrogen peroxide - a colorless, odorless, hardly evaporable liquid that dissolves other substances well. The result of the interaction of H2O2 and H2O2 is a dissociation reaction, the peroxide is soluble in water.

An interesting fact is that the properties of the new substance were quickly discovered, allowing it to be used in restoration work. Tenard himself, using peroxide, restored the painting by Raphael, which had darkened with time.

Hydrogen peroxide in the 20th century

After a thorough study of the resulting substance, it began to be produced on an industrial scale. At the beginning of the twentieth century, an electrochemical technology for the production of peroxide was introduced, based on the electrolysis process. But the shelf life of the substance obtained by this method was small, about a couple of weeks. Pure peroxide is unstable, and for the most part it was produced in a thirty percent concentration for bleaching fabrics and in three or six percent for domestic use.

Scientists in Nazi Germany used peroxide to create a liquid fuel rocket engine that was used for defense purposes in World War II. As a result of the interaction of H2O2 and methanol / hydrazine, a powerful fuel was obtained, on which the aircraft reached speeds of more than 950 km / h.

Where is H2O2 used now?

• in medicine - for the treatment of wounds;
• in the pulp and paper industry, the bleaching properties of the substance are used;
• in the textile industry, natural and synthetic fabrics, furs, wool are bleached with peroxide;
• as rocket fuel or its oxidizer;
• in chemistry - to produce oxygen, as a foaming agent for the production of porous materials, as a catalyst or hydrogenating agent;
• for the production of disinfectants or cleaning agents, bleaches;
• for bleaching hair (this is an outdated method, since the hair is severely damaged by peroxide);

Hydrogen peroxide can be successfully used to solve various household problems. But only 3% hydrogen peroxide can be used for these purposes. Here are some ways:

• To clean surfaces, pour peroxide into a container with a spray bottle and spray on contaminated areas.
• For disinfection of objects, they must be wiped with an undiluted solution of H2O2. This will help cleanse them of harmful microorganisms. Sponges for washing can be soaked in water with peroxide (proportion 1:1).
• To bleach fabrics when washing white things, add a glass of peroxide. You can also rinse white fabrics in water mixed with a glass of H2O2. This method restores whiteness, prevents fabrics from yellowing and helps remove stubborn stains.
• To combat mold and mildew, mix peroxide and water in a spray bottle in a ratio of 1:2. Spray the resulting mixture on infected surfaces and clean them with a brush or sponge after 10 minutes.
• You can update the darkened grout in the tile by spraying peroxide on the desired areas. After 30 minutes, you need to carefully rub them with a stiff brush.
• To wash dishes, add half a glass of H2O2 to a full basin of water (or a sink with a closed drain). Cups and plates washed in such a solution will shine with cleanliness.
• To clean your toothbrush, you need to dip it in an undiluted 3% peroxide solution. Then rinse under strong running water. This method disinfects the hygiene item well.
• To disinfect purchased vegetables and fruits, spray a solution of 1 part peroxide and 1 part water on them, then rinse them thoroughly with water (can be cold).
• In the suburban area with the help of H2O2, you can fight plant diseases. You need to spray them with a peroxide solution or soak the seeds shortly before planting in 4.5 liters of water mixed with 30 ml of forty percent hydrogen peroxide.
• To revive aquarium fish, if they are poisoned by ammonia, suffocated when aeration is turned off, or for another reason, you can try placing them in water with hydrogen peroxide. It is necessary to mix 3% peroxide with water at the rate of 30 ml per 100 liters and place it in the resulting mixture of lifeless fish for 15-20 minutes. If they do not come to life during this time, then the remedy did not help.

Even as a result of vigorous shaking of a water bottle, a certain amount of peroxide is formed in it, since the water is saturated with oxygen during this action.

Fresh fruits and vegetables also contain H2O2 until they are cooked. During heating, boiling, roasting and other processes with an accompanying high temperature, a large amount of oxygen is destroyed. That is why cooked foods are considered not so useful, although some amount of vitamins remains in them. Freshly squeezed juices or oxygen cocktails served in sanatoriums are useful for the same reason - due to oxygen saturation, which gives the body new strength and cleanses it.

The dangers of peroxide when ingested

After the above, it may seem that peroxide can be specifically taken orally, and this will benefit the body. But that's not the case at all. In water or juices, the compound is found in minimal amounts and is closely related to other substances. Taking “unnatural” hydrogen peroxide inside (and all peroxide bought in a store or produced as a result of chemical experiments on your own cannot be considered natural in any way, besides, it has too high a concentration compared to natural) can lead to life-threatening and health-threatening consequences. To understand why, you need to turn to chemistry again.

As already mentioned, under certain conditions, hydrogen peroxide breaks down and releases oxygen, which is an active oxidizing agent. can occur when H2O2 collides with peroxidase, an intracellular enzyme. The use of peroxide for disinfection is based on its oxidizing properties. So, when a wound is treated with H2O2, the released oxygen destroys the living pathogenic microorganisms that have entered it. It has the same effect on other living cells. If you treat intact skin with peroxide, and then wipe the area with alcohol, you will feel a burning sensation, which confirms the presence of microscopic damage after peroxide. But with the external use of peroxide at a low concentration, there will be no noticeable harm to the body.

Another thing, if you try to take it inside. That substance, which is capable of damaging even relatively thick skin from the outside, enters the mucous membranes of the digestive tract. That is, chemical mini-burns occur. Of course, the released oxidizing agent - oxygen - can also kill harmful microbes. But the same process will occur with the cells of the alimentary tract. If burns as a result of the action of an oxidizing agent are repeated, then atrophy of the mucous membranes is possible, and this is the first step towards cancer. The death of intestinal cells leads to the inability of the body to absorb nutrients, this explains, for example, weight loss and the disappearance of constipation in some people who practice peroxide "treatment".

Separately, it must be said about such a method of using peroxide as intravenous injections. Even if for some reason they were prescribed by a doctor (this can only be justified in case of blood poisoning, when there are no other suitable drugs available), then under medical supervision and with a strict calculation of dosages, there are still risks. But in such extreme situation it will be a chance for recovery. In no case should you prescribe yourself injections of hydrogen peroxide. H2O2 poses a great danger to blood cells - erythrocytes and platelets, as it destroys them when it enters the bloodstream. In addition, a deadly blockage of blood vessels by released oxygen can occur - a gas embolism.

Safety measures in handling H2O2

• Keep out of the reach of children and incapacitated persons. The lack of smell and pronounced taste makes peroxide especially dangerous for them, as large doses can be taken. If the solution is ingested, the consequences of use can be unpredictable. You must immediately consult a doctor.
• Peroxide solutions with a concentration of more than three percent cause burns if it comes into contact with the skin. The burn area should be washed with plenty of water.

• Do not allow the peroxide solution to get into the eyes, as their swelling, redness, irritation, and sometimes pain are formed. First aid before going to the doctor - plentiful rinsing of the eyes with water.
• Store the substance in such a way that it is clear that it is H2O2, that is, in a container with a sticker to avoid accidental misuse.
• Storage conditions that extend its life are a dark, dry, cool place.
• Do not mix hydrogen peroxide with any liquids other than pure water, including chlorinated tap water.
• All of the above applies not only to H2O2, but to all preparations containing it.