What does the formula h2o. Properties of water - chemical and physical properties of water in a liquid state
Other names: hydrogen oxide, dihydrogen monoxide.
Water - inorganic compound with the chemical formula H 2 O.
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 matter. 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 in the second and third distillations with the addition of 3 g of KHSO 4 or 5 ml of 20% H 3 PO 4 , these reagents being preheated with a small amount of 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. The water of the highest purity required for conducting conductivity measurements is obtained by particularly careful distillation of water that has already been very well purified. 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
- 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.
- 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, the scientists Tenard and Gay-Lussac conducted an experiment on the combustion of alkali metals with an excess of oxygen, as a result of which sodium peroxide was obtained. 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 Nazi Germany used peroxide to create a liquid-propellant 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.
- To disinfect 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 onto 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.
DEFINITION
Water (hydrogen oxide) is a binary inorganic compound.
Chemical formula: H 2 O
Structural formula:
Molar mass: 18.01528 g/mol.
Alternative titles: oxide, hydrogen hydroxide, hydroxyl acid, dihydrogen monoxide, oxidane, dihydromonoxide.
In a water molecule, the oxygen atom is in the sp 3 hybridization state, since not only valence electrons, but also unshared electron pairs participate in the formation of hybrid orbitals. Hybrid orbitals are directed to the vertices of the tetrahedron:
Due to the large difference in the electronegativity of oxygen and hydrogen, the bonds in the molecule are strongly polarized, and the electron is shifted towards . The water molecule has a large dipole moment because the polar bonds are not symmetrical.
The formation of hydrogen bonds between water molecules. Each water molecule can form up to four hydrogen bonds - two of them form an oxygen atom, and two more - hydrogen atoms:
The formation of hydrogen bonds determines the higher boiling point, viscosity and surface tension of water in comparison with hydrides of analogues (selenium and tellurium).
Isotope modifications of water
Depending on the type of hydrogen isotopes that make up the molecule, the following are distinguished: isotope modifications of water:
Taking into account that oxygen has three stable isotopes (16 O, 17 O and 18 O), 18 formulas of water molecules with different isotopic compositions can be made. As a rule, natural water contains all 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 alcohol with a density of 0.8 g/ml were added. At what minimum temperature can you now leave the car for 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 non-electrolytes is:
where: - lowering the freezing point of the solution; K cr is the cryoscopic constant of the solvent; Cm is the molar concentration of the solution; m B is the mass of the dissolved substance; m A is the mass of the solvent; M B is the molar mass of the solute. The mass of methyl alcohol is: The mass of water is: The molar mass of methyl alcohol is 32g/mol 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 must 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 the dissolved salt as x. Then the solution will be equal to: The mass of anhydrous salt in the finished solution will be equal to: |
Water (hydrogen oxide) is a binary inorganic compound with the chemical formula H 2 O. The water molecule consists of two hydrogen atoms and one oxygen, which are interconnected by a covalent bond.
Hydrogen peroxide.
Physical and chemical properties
Physical and Chemical properties waters are determined by chemical, electronic and spatial structure H 2 O molecules.
The H and O atoms in the H 2 0 molecule are in their stable oxidation states, respectively +1 and -2; therefore, water does not exhibit pronounced oxidizing or reducing properties. Please note: in metal hydrides, hydrogen is in the -1 oxidation state.
The H 2 O molecule has an angular structure. H-O bonds very polar. There is an excess negative charge on the O atom, and excess positive charges on the H atoms. In general, the H 2 O molecule is polar, i.e. dipole. This explains the fact that water is a good solvent for ionic and polar substances.
The presence of excess charges on H and O atoms, as well as unshared electron pairs at O atoms, causes the formation of hydrogen bonds between water molecules, as a result of which they combine into associates. The existence of these associates explains the anomalously high values of mp. etc. kip. water.
Along with the formation of hydrogen bonds, the result of the mutual influence of H 2 O molecules on each other is their self-ionization:
in one molecule there is a heterolytic break of the polar O-N connections, and the released proton joins the oxygen atom of another molecule. The resulting hydroxonium ion H 3 O + is essentially a hydrated hydrogen ion H + H 2 O, therefore, the water self-ionization equation is simplified as follows:
H 2 O ↔ H + + OH -
The dissociation constant of water is extremely small:
This indicates that water very slightly dissociates into ions, and therefore the concentration of undissociated H 2 O molecules is almost constant:
AT clean water[H +] \u003d [OH -] \u003d 10 -7 mol / l. This means that water is a very weak amphoteric electrolyte that exhibits neither acidic nor basic properties to a noticeable degree.
However, water has a strong ionizing effect on the electrolytes dissolved in it. Under the action of water dipoles, polar covalent bonds in the molecules of dissolved substances are converted into ionic ones, ions are hydrated, the bonds between them are weakened, as a result of which electrolytic dissociation. For example:
HCl + H 2 O - H 3 O + + Cl -
(strong electrolyte)
(or excluding hydration: HCl → H + + Cl -)
CH 3 COOH + H 2 O ↔ CH 3 COO - + H + (weak electrolyte)
(or CH 3 COOH ↔ CH 3 COO - + H +)
According to the Bronsted-Lowry theory of acids and bases, in these processes, water exhibits the properties of a base (proton acceptor). According to the same theory, water acts as an acid (proton donor) in reactions, for example, with ammonia and amines:
NH 3 + H 2 O ↔ NH 4 + + OH -
CH 3 NH 2 + H 2 O ↔ CH 3 NH 3 + + OH -
Redox reactions involving water
I. Reactions in which water plays the role of an oxidizing agent
These reactions are possible only with strong reducing agents, which are able to reduce the hydrogen ions that are part of the water molecules to free hydrogen.
1) Interaction with metals
a) Under normal conditions, H 2 O interacts only with alkali. and alkali-earth. metals:
2Na + 2H + 2 O \u003d 2NaOH + H 0 2
Ca + 2H + 2 O \u003d Ca (OH) 2 + H 0 2
b) At high temperatures, H 2 O also reacts with some other metals, for example:
Mg + 2H + 2 O \u003d Mg (OH) 2 + H 0 2
3Fe + 4H + 2 O \u003d Fe 2 O 4 + 4H 0 2
c) Al and Zn displace H 2 from water in the presence of alkalis:
2Al + 6H + 2 O + 2NaOH \u003d 2Na + 3H 0 2
2) Interaction with non-metals having low EO (reactions occur under harsh conditions)
C + H + 2 O \u003d CO + H 0 2 ("water gas")
2P + 6H + 2 O \u003d 2HPO 3 + 5H 0 2
In the presence of alkalis, silicon displaces hydrogen from water:
Si + H + 2 O + 2NaOH \u003d Na 2 SiO 3 + 2H 0 2
3) Interaction with metal hydrides
NaH + H + 2 O \u003d NaOH + H 0 2
CaH 2 + 2H + 2 O \u003d Ca (OH) 2 + 2H 0 2
4) Interaction with carbon monoxide and methane
CO + H + 2 O \u003d CO 2 + H 0 2
2CH 4 + O 2 + 2H + 2 O \u003d 2CO 2 + 6H 0 2
Reactions are used in industry to produce hydrogen.
II. Reactions in which water acts as a reducing agent
These reactions are possible only with very strong oxidizing agents that are capable of oxidizing oxygen CO CO -2, which is part of water, to free oxygen O 2 or to peroxide anions 2-. In an exceptional case (in reaction with F 2), oxygen is formed with c o. +2.
1) Interaction with fluorine
2F 2 + 2H 2 O -2 \u003d O 0 2 + 4HF
2F 2 + H 2 O -2 \u003d O +2 F 2 + 2HF
2) Interaction with atomic oxygen
H 2 O -2 + O \u003d H 2 O - 2
3) Interaction with chlorine
At high T, a reversible reaction occurs
2Cl 2 + 2H 2 O -2 \u003d O 0 2 + 4HCl
III. Reactions of intramolecular oxidation - reduction of water.
Under the influence electric current or high temperature, water can be decomposed into hydrogen and oxygen:
2H + 2 O -2 \u003d 2H 0 2 + O 0 2
Thermal decomposition is a reversible process; the degree of thermal decomposition of water is low.
Hydration reactions
I. Hydration of ions. The ions formed during the dissociation of electrolytes in aqueous solutions attach a certain number of water molecules and exist in the form of hydrated ions. Some ions form such strong bonds with water molecules that their hydrates can exist not only in solution, but also in the solid state. This explains the formation of crystalline hydrates such as CuSO4 5H 2 O, FeSO 4 7H 2 O, etc., as well as aqua complexes: CI 3 , Br 4 , etc.
II. Hydration of oxides
III. Hydration organic compounds containing multiple bonds
Hydrolysis reactions
I. Hydrolysis of salts
Reversible hydrolysis:
a) according to the salt cation
Fe 3+ + H 2 O \u003d FeOH 2+ + H +; (acidic environment. pH
b) by salt anion
CO 3 2- + H 2 O \u003d HCO 3 - + OH -; (alkaline environment. pH > 7)
c) by the cation and by the anion of the salt
NH 4 + + CH 3 COO - + H 2 O \u003d NH 4 OH + CH 3 COOH (environment close to neutral)
Irreversible hydrolysis:
Al 2 S 3 + 6H 2 O \u003d 2Al (OH) 3 ↓ + 3H 2 S
II. Hydrolysis of metal carbides
Al 4 C 3 + 12H 2 O \u003d 4Al (OH) 3 ↓ + 3CH 4 netane
CaC 2 + 2H 2 O \u003d Ca (OH) 2 + C 2 H 2 acetylene
III. Hydrolysis of silicides, nitrides, phosphides
Mg 2 Si + 4H 2 O \u003d 2Mg (OH) 2 ↓ + SiH 4 silane
Ca 3 N 2 + 6H 2 O \u003d ZCa (OH) 2 + 2NH 3 ammonia
Cu 3 P 2 + 6H 2 O \u003d ZCu (OH) 2 + 2PH 3 phosphine
IV. Hydrolysis of halogens
Cl 2 + H 2 O \u003d HCl + HClO
Br 2 + H 2 O \u003d HBr + HBrO
V. Hydrolysis of organic compounds
Classes of organic substances |
Hydrolysis products (organic) |
Halogenalkanes (alkyl halides) |
|
Aryl halides |
|
Dihaloalkanes |
Aldehydes or ketones |
Metal alcoholates |
|
Carboxylic acid halides |
carboxylic acids |
Anhydrides of carboxylic acids |
carboxylic acids |
Esters of carboxylic acids |
Carboxylic acids and alcohols |
Glycerin and higher carboxylic acids |
|
Di- and polysaccharides |
Monosaccharides |
Peptides and proteins |
α-Amino acids |
Nucleic acids |
|
Formulas for covalent bonds are fundamentally different from formulas for ionic bonds. The fact is that covalent compounds can be formed in a variety of 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 full description covalent compound 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 concise 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