What foods contain chromium, and how is it good for the body? Chrome element. Chromium properties. Application of chromium

Project Web Lab launched by Google in collaboration with the London Science Museum. It is a museum exhibition of five exhibits and a website where you can access them online. The main idea of the project is to allow website visitors to interact in real time with real exhibits. Each of them is dedicated to a specific technology, the project will be valid until June 2013.

To see the museum exhibits in action, go to the laboratory's website. Please note that the browser and video card of the computer must support WebGL technology. In the absence of such support, you will be notified of this on the main page of the site. If everything is in order, click the enter button, then select the exhibit you are interested in on the page that opens.

The first exhibit is the Universal Orchestra. By launching it, you can play on eight installed in the museum musical instruments by creating your own tunes. Control is carried out with the mouse. Since there is only one exhibit, and there are many visitors, it may be necessary to stand in an online queue.

The Sketchbots exhibit is very interesting. A computer webcam takes your photo, it is immediately processed, turning into an outline picture. By clicking the Submit button, you can submit it to the museum. After that, the robotic arm installed in it will quickly draw your portrait on the sand. True, in this case you will have to stand in a rather big line. Ready portrait unfortunately will be erased later.

The Teleporter exhibit allows you to control panoramic webcams installed in several locations around the world - in a cafe in North Carolina, in an entertainment center in Holland and in the Cape Town Aquarium. Having selected this museum exhibit, you will see three round windows corresponding to the three installed webcams. Choose any of them - for example, the first one. You will immediately "teleport" to a cafe in North Carolina, you will see an image from the camera installed in it. You can rotate it 360o with the mouse, this will give you a full panoramic view. In addition, you will be able to take photos of what you observe. Picture from entertainment center less interesting, but the panorama from the Cape Town Marine Aquarium will allow you to watch the fish. By turning the camera, you can follow any inhabitant of the aquarium you like.

The next exhibit in the museum is Data Tracer. It allows you to find where a particular file is physically stored. Compared to the previous exhibits, it is less interesting and simply shows the path to a specific point on the map. The same can be said for the museum's fifth exhibit, the Lab Tag Explorer, which shows on a map where the lab's visitors are and also counts their number. By visiting the laboratory's website, you can independently test all the exhibits of the London Science Museum.

Chromium is a chemical element with atomic number 24. It is a hard, shiny, steel-gray metal that polishes well and does not tarnish. Used in alloys such as stainless steel, and as a coating. The human body requires small amounts of trivalent chromium to metabolize sugar, but Cr (VI) is highly toxic.

Various chromium compounds such as chromium (III) oxide and lead chromate are brightly colored and used in paints and pigments. The red color of the ruby is due to the presence of this chemical element... Some substances, especially sodium, are oxidizing agents used to oxidize organic compounds and (along with sulfuric acid) to clean laboratory glassware. In addition, chromium (VI) oxide is used in the production of magnetic tape.

Discovery and etymology

The history of the discovery of the chemical element chromium is as follows. In 1761, Johann Gottlob Lehmann found an orange-red mineral in the Ural Mountains and called it "Siberian red lead." Although it was mistakenly identified as a compound of lead with selenium and iron, the material was actually lead chromate with chemical formula PbCrO 4. Today it is known as the mineral croconte.

In 1770, Peter Simon Pallas visited the place where Lehmann found a red lead mineral, which had a very beneficial features pigment in paints. The use of Siberian red lead as a paint developed rapidly. Also, bright yellow from croconte has become fashionable.

In 1797, Nicolas-Louis Vauquelin received samples of red. By mixing croconte with hydrochloric acid, he obtained the oxide CrO 3. Chromium was isolated as a chemical element in 1798. Vauquelin got it by heating oxide with charcoal. He was also able to detect traces of chromium in precious stones such as ruby and emerald.

In the 1800s, Cr was mainly used in paints and leather salts. Today 85% of the metal is used in alloys. The rest applies to chemical industry, the production of refractory materials and the foundry industry.

The pronunciation of the chemical element chromium corresponds to the Greek χρῶμα, which means "color", due to the many colored compounds that can be obtained from it.

Extraction and production

The element is produced from chromite (FeCr 2 O 4). About half of this ore in the world is mined in South Africa... In addition, Kazakhstan, India and Turkey are major producers. There are enough explored deposits of chromite, but geographically they are concentrated in Kazakhstan and southern Africa.

Native metallic chromium deposits are rare, but they do exist. For example, it is mined at the Udachnaya mine in Russia. It is rich in diamonds and the reducing environment has helped to form pure chromium and diamonds.

For industrial production metal chromite ores are treated with molten alkali (sodium hydroxide, NaOH). In this case, sodium chromate (Na 2 CrO 4) is formed, which is reduced with carbon to oxide Cr 2 O 3. The metal is obtained by heating the oxide in the presence of aluminum or silicon.

In 2000, about 15 million tonnes of chromite ore were mined, which was processed into 4 million tonnes of ferrochrome, 70% chromium-iron alloy, with an approximate market value of US $ 2.5 billion.

Main characteristics

The characteristic of the chemical element chromium is due to the fact that it is a transition metal of the fourth period of the periodic table and is located between vanadium and manganese. It is included in the VI group. Melts at 1907 ° C. In the presence of oxygen, chromium quickly forms a thin oxide layer that protects the metal from further interaction with oxygen.

As a transitional element, it reacts with substances in different ratios... Thus, it forms compounds in which it has various oxidation states. Chromium is a chemical element with basic states +2, +3 and +6, of which +3 is the most stable. In addition, on rare occasions, states +1, +4, and +5 are observed. Chromium compounds in the +6 oxidation state are strong oxidizing agents.

What color is chrome? The chemical element imparts a ruby hue. Cr 2 O 3 used for is also applied as a pigment called "chrome green". Its salts color the glass an emerald green color. Chromium is a chemical element whose presence makes ruby red. Therefore, it is used in the production of synthetic rubies.

Isotopes

Chromium isotopes have an atomic weight of 43 to 67. Usually this chemical element consists of three stable forms: 52 Cr, 53 Cr and 54 Cr. Of these, the most common is 52 Cr (83.8% of all natural chromium). In addition, 19 radioisotopes have been described, of which the most stable is 50 Cr with a half-life exceeding 1.8x10 17 years. For 51 Cr, the half-life is 27.7 days, while for all other radioactive isotopes it does not exceed 24 hours, and for most of them it lasts less than one minute. The item also has two meta states.

Chromium isotopes in the earth's crust, as a rule, accompany manganese isotopes, which is used in geology. 53 Cr is formed during the radioactive decay of 53 Mn. Mn / Cr isotope ratio supports other early history Solar system... Changes in the 53 Cr / 52 Cr and Mn / Cr ratios from different meteorites prove that new atomic nuclei were created just before the formation of the solar system.

Chemical element chromium: properties, formula of compounds

Chromium (III) oxide Cr 2 O 3, also known as sesquioxide, is one of the four oxides of this chemical element. It is obtained from chromite. The green compound is commonly referred to as "chrome green" when used as a pigment for enamel and glass painting. Oxide can dissolve in acids, forming salts, and in molten alkali - chromites.

Potassium dichromate

K 2 Cr 2 O 7 is a powerful oxidizing agent and is preferred as a detergent for cleaning laboratory glassware from organics. For this, its saturated solution is used. Sometimes, however, it is replaced with sodium dichromate, based on the higher solubility of the latter. In addition, it can regulate the oxidation process of organic compounds by converting primary alcohol into aldehyde and then into carbon dioxide.

Potassium dichromate can cause chromium dermatitis. Chromium is probably the cause of sensitization leading to the development of dermatitis, especially of the hands and arms, which is chronic and difficult to treat. Like other Cr (VI) compounds, potassium dichromate is carcinogenic. It must be handled with gloves and appropriate protective equipment.

Chromic acid

The compound has a hypothetical structure H 2 CrO 4. Neither chromic nor dichromic acids occur naturally, but their anions are found in various substances... The "chromic acid" that can be found on the market is actually its acidic anhydride - trioxide CrO 3.

Lead (II) chromate

PbCrO 4 has a bright yellow color and is practically insoluble in water. For this reason, it has found application as a coloring pigment called yellow crown.

Cr and pentavalent bond

Chromium is distinguished by its ability to form pentavalent bonds. The compound is created by Cr (I) and a hydrocarbon radical. A pentavalent bond is formed between two chromium atoms. Its formula can be written as Ar-Cr-Cr-Ar, where Ar is a specific aromatic group.

Application

Chromium is a chemical element, the properties of which have provided it with many different options applications, some of which are listed below.

It imparts corrosion resistance and a glossy surface to metals. Therefore, chromium is included in alloys such as stainless steel, used, for example, in cutlery. It is also used for chrome plating.

Chromium is a catalyst for various reactions. Molds for baking bricks are made from it. Its leather is tanned with salts. Potassium dichromate is used to oxidize organic compounds such as alcohols and aldehydes, and to clean laboratory glassware. It serves as a fixing agent for dyeing fabrics and is also used in photography and photo printing.

CrO 3 is used for the manufacture of magnetic tapes (for example, for audio recording), which have the best characteristics than films with iron oxide.

Role in biology

Trivalent chromium is a chemical element necessary for the metabolism of sugar in the human body. In contrast, hexavalent Cr is highly toxic.

Precautionary measures

Chromium metal and Cr (III) compounds are generally not considered hazardous to health, but substances containing Cr (VI) can be toxic if ingested or inhaled. Most of these substances are irritating to the eyes, skin and mucous membranes. Chromium (VI) compounds can cause eye damage if not properly treated with chronic exposure. It is also a recognized carcinogen. The lethal dose of this chemical element is about half a teaspoon. According to the recommendations of the World Health Organization, the maximum permissible concentration of Cr (VI) in drinking water is 0.05 mg per liter.

Since chromium compounds are used in dyes and for tanning leather, they are often found in soil and groundwater abandoned industrial facilities requiring environmental cleaning and restoration. A primer containing Cr (VI) is still widely used in the aerospace and automotive industries.

Element properties

The main physical properties of chromium are as follows:

Atomic number: 24.
Atomic Weight: 51.996
Melting point: 1890 ° C.
Boiling point: 2482 ° C.
Oxidation state: +2, +3, +6.
Electron configuration: 3d 5 4s 1.

You can often find such a thing as "chrome surface", and stainless steel is familiar to almost every inhabitant of the planet. What do they have in common? The correct answer is chrome. Let's find out what chromium is and where it is used, what are its properties and role in human life.

Chromium is a hard metal that has a bluish-gray color. It is in the 6th group of the 4th period of the periodic table. Has atomic number 24 and designation Cr.

Physical properties of chromium

The melting point of chromium is 2130 degrees Kelvin, and the boiling point is 2945 Kelvin. The metal has a cubic crystal lattice and a hardness of 5 on the Mohs scale. Chromium is one of the most hard metals(in pure form) and is second only to Uranium, beryllium, iridium and tungsten in terms of indicators. Refined chrome lends itself easily machining.

Chemical properties of chromium

Chromium has several oxidation states that significantly affect its properties and color.

The oxidation state +2 is blue and is a very good reducing agent.
Oxidation state +3 - green or purple amphoteric oxide.
The oxidation state +4 is a very rare compound, does not form salts and has the usual color - silver.
Oxidation state +6 is a very strong oxidizing agent, hygroscopic and very toxic. The chromates of this oxide are yellow and the dichromates are orange.

As a simple substance, it is stable in air. Does not react with sulfuric and nitrous acids. At temperatures over 2000 degrees Celsius, it burns out and forms green chromium oxide.

There are compounds of chromium with boron, carbon, nitrogen and silicon.

Application of chromium

Chromium is used to create stainless alloys. All of us known stainless steel is created using chrome.
Chromium is used as an electroplating coating. You've probably seen chrome metal surfaces. They can be recognized by their beautiful mirror shine. Chrome-plated products are less susceptible to atmospheric corrosion (do not rust).
Various chromium alloys are used to create nozzles for aircraft and rocket engines, as well as for the production of plasma torch nozzles.
Heating elements are made from an alloy of chromium and nickel.
Various dyes are made from chromium compounds, as well as compounds for tanning leather.

If you are interested in the meanings of other terms, visit

Hard metal, bluish-white in color. Chromium is sometimes referred to as ferrous metals. This metal is capable of coloring compounds in different colors, therefore it was named "chrome", which means "paint". Chromium is a trace element necessary for the normal development and functioning of the human body. Its most important biological role is in the regulation of carbohydrate metabolism and blood glucose levels.

See also:

STRUCTURE

Depending on the types of chemical bonds - like all metals, chromium has a metallic type of crystal lattice, that is, a metal atom is located at the lattice sites.
Depending on the spatial symmetry - cubic, body-centered a = 0.28839 nm. A feature of chromium is a sharp change in its physical properties at a temperature of about 37 ° C. The crystal lattice of a metal consists of its ions and mobile electrons. Similarly, the chromium atom in the ground state has an electronic configuration. At 1830 ° C, the transformation into a modification with a face-centered lattice is possible, a = 3.69 Å.

PROPERTIES

Chromium has a Mohs hardness of 9, one of the hardest pure metals (second only to iridium, beryllium, tungsten and uranium). Very pure chrome can be machined fairly well. Stable in air due to passivation. For the same reason, it does not react with sulfuric and nitric acids. Burns at 2000 ° C with the formation of green chromium (III) oxide Cr 2 O 3, which has amphoteric properties. When heated, it reacts with many non-metals, often forming compounds of non-stoichiometric composition, carbides, borides, silicides, nitrides, etc. Chromium forms numerous compounds in various oxidation states, mainly +2, +3, +6. Chromium has all the properties characteristic of metals - it conducts heat well, electricity, has the luster inherent in most metals. It is an antiferromagnet and a paramagnet, that is, at a temperature of 39 ° C, it passes from a paramagnetic state to an antiferromagnetic state (Neel point).

RESERVES AND PRODUCTION

The largest chromium deposits are located in South Africa (1st place in the world), Kazakhstan, Russia, Zimbabwe, Madagascar. There are also deposits in Turkey, India, Armenia, Brazil, the Philippines. The main deposits of chrome ores in the Russian Federation are known in the Urals (Donskoye and Saranovskoye). Explored reserves in Kazakhstan amount to over 350 million tons (2nd place in the world) Chromium occurs in nature mainly in the form of chromium iron ore Fe (CrO 2) 2 (iron chromite). Ferrochrome is obtained from it by reduction in electric furnaces with coke (carbon). To obtain pure chromium, the reaction is carried out as follows:
1) alloy iron chromite with sodium carbonate (soda ash) in air;
2) dissolve sodium chromate and separate it from iron oxide;
3) transfer chromate to dichromate, acidifying the solution and crystallizing the dichromate;
4) pure chromium oxide is obtained by reduction of sodium dichromate with coal;
5) metal chromium is obtained with the help of aluminothermy;
6) using electrolysis, electrolytic chromium is obtained from a solution of chromic anhydride in water containing an additive of sulfuric acid.

ORIGIN

The average content of Chromium in the earth's crust (clarke) is 8.3 · 10 -3%. This element is probably more characteristic of the Earth's mantle, since the ultrabasic rocks, which are believed to be the closest in composition to the Earth's mantle, are enriched in Chromium (2 · 10 -4%). Chromium forms massive and disseminated ores in ultrabasic rocks; the formation of the largest deposits of chromium is associated with them. In basic rocks, the chromium content reaches only 2 · 10 -2%, in acidic rocks - 2.5 · 10 -3%, in sedimentary rocks (sandstones) - 3.5 · 10 -3%, shales - 9 · 10 -3 %. Chromium is a relatively weak water migrant; Chromium content in sea water 0.00005 mg / l.
In general, Chromium is a metal of the deep zones of the Earth; stone meteorites (analogs of the mantle) are also enriched in chromium (2.7 · 10 -1%). More than 20 chromium minerals are known. Only chrome spinels (up to 54% Cr) are of industrial importance; in addition, chromium is contained in a number of other minerals that often accompany chromium ores, but themselves are not of practical value (uvarovite, volkonskoite, kemerite, fuchsite).
There are three main chromium minerals: magnochromite (Mg, Fe) Cr 2 O 4, chromopicotite (Mg, Fe) (Cr, Al) 2 O 4 and alumochromite (Fe, Mg) (Cr, Al) 2 O 4. By appearance they are indistinguishable and are inaccurately called "chromites."

APPLICATION

Chromium is an important component in many alloy steels (in particular, stainless steels), as well as in a number of other alloys. The addition of chromium significantly increases the hardness and corrosion resistance of the alloys. The use of Chromium is based on its heat resistance, hardness and corrosion resistance. Most of all Chromium is used for smelting chromium steels. Aluminum and silicothermic Chromium is used to smelt nichrome, nimonic, other nickel alloys and stellite.
A significant amount of Chromium goes to decorative corrosion-resistant coatings... Chromium powder is widely used in the production of cermet products and materials for welding electrodes. Chromium in the form of Cr 3+ ion is an impurity in ruby, which is used as precious stone and laser material... Chromium compounds are used to etch fabrics during dyeing. Some Chromium salts are used as component tanning solutions in the leather industry; PbCrO 4, ZnCrO 4, SrCrO 4 - as artistic paints. Chromite-magnesite refractory products are made from a mixture of chromite and magnesite.
It is used as a wear-resistant and beautiful electroplated coating (chrome plating).
Chromium is used for the production of alloys: chromium-30 and chromium-90, indispensable for the production of powerful plasma torches nozzles and in the aerospace industry.

Chromium - Cr

National Research Tomsk Polytechnic University

Institute of Natural Resources Geoecology and Geochemistry

Chromium

By discipline:

Chemistry

Completed:

student of group 2G41 Tkacheva Anastasia Vladimirovna 10/29/2014

Checked:

teacher Stas Nikolay Fedorovich

Position in the periodic system

Chromium- an element of a side subgroup of the 6th group of the 4th period of the periodic system of chemical elements of D.I.Mendeleev with atomic number 24. It is designated by the symbol Cr(lat. Chromium). Simple substance chromium- solid metal, bluish-white. Chromium is sometimes referred to as ferrous metals.

Atom structure

17 Cl) 2) 8) 7 - diagram of the structure of the atom

1s2s2p3s3p- electronic formula

The atom is located in the III period, and has three energy levels

The atom is located in VII in the group, in the main subgroup - at the external energy level of 7 electrons

Element properties

Physical properties

Chromium is a white shiny metal with a cubic body-centered lattice, a = 0.28845 nm, characterized by hardness and brittleness, with a density of 7.2 g / cm 3, one of the hardest pure metals (second only to beryllium, tungsten and uranium), with a melting point of 1903 degrees. And with a boiling point of about 2570 degrees. C. In air, the surface of chromium is covered with an oxide film, which protects it from further oxidation. The addition of carbon to chromium further increases its hardness.

Chemical properties

Chromium under normal conditions is an inert metal; when heated, it becomes quite active.

Interaction with non-metals

When heated above 600 ° C, chromium burns out in oxygen:

4Cr + 3O 2 = 2Cr 2 O 3.

It reacts with fluorine at 350 ° С, with chlorine - at 300 ° С, with bromine - at the temperature of red heat, forming chromium (III) halides:

2Cr + 3Cl 2 = 2CrCl 3.

Reacts with nitrogen at temperatures above 1000 ° C with the formation of nitrides:

2Cr + N 2 = 2CrN

or 4Cr + N 2 = 2Cr 2 N.

2Cr + 3S = Cr 2 S 3.

Reacts with boron, carbon and silicon to form borides, carbides and silicides:

Cr + 2B = CrB 2 (formation of Cr 2 B, CrB, Cr 3 B 4, CrB 4 is possible),

2Cr + 3C = Cr 2 C 3 (formation of Cr 23 C 6, Cr 7 B 3 is possible),

Cr + 2Si = CrSi 2 (formation of Cr 3 Si, Cr 5 Si 3, CrSi is possible).

Does not directly interact with hydrogen.

Interaction with water

In a finely divided incandescent state, chromium reacts with water, forming chromium (III) oxide and hydrogen:

2Cr + 3H 2 O = Cr 2 O 3 + 3H 2

5interactions with acids

In the electrochemical series of metal voltages, chromium is up to hydrogen, it displaces hydrogen from solutions of non-oxidizing acids:

Cr + 2HCl = CrCl 2 + H 2;

Cr + H 2 SO 4 = CrSO 4 + H 2.

In the presence of atmospheric oxygen, chromium (III) salts are formed:

4Cr + 12HCl + 3O 2 = 4CrCl 3 + 6H 2 O.

Concentrated nitric and sulfuric acids passivate chromium. Chromium can dissolve in them only with strong heating, chromium (III) salts and acid reduction products are formed:

2Cr + 6H 2 SO 4 = Cr 2 (SO 4) 3 + 3SO 2 + 6H 2 O;

Cr + 6HNO 3 = Cr (NO 3) 3 + 3NO 2 + 3H 2 O.

Interaction with alkaline reagents

In aqueous solutions of alkalis, chromium does not dissolve, slowly reacts with alkali melts with the formation of chromites and the release of hydrogen:

2Cr + 6KOH = 2KCrO 2 + 2K 2 O + 3H 2.

Reacts with alkaline melts of oxidizing agents, for example potassium chlorate, while chromium is converted to potassium chromate:

Cr + KClO 3 + 2KOH = K 2 CrO 4 + KCl + H 2 O.

Recovery of metals from oxides and salts

Chromium is an active metal capable of displacing metals from solutions of their salts: 2Cr + 3CuCl 2 = 2CrCl 3 + 3Cu.

Properties of a simple substance

Stable in air due to passivation. For the same reason, it does not react with sulfuric and nitric acids. Burns at 2000 ° C with the formation of green chromium (III) oxide Cr 2 O 3, which has amphoteric properties.

Compounds of chromium with boron were synthesized (borides Cr 2 B, CrB, Cr 3 B 4, CrB 2, CrB 4 and Cr 5 B 3), with carbon (carbides Cr 23 C 6, Cr 7 C 3 and Cr 3 C 2), with silicon (silicides Cr 3 Si, Cr 5 Si 3 and CrSi) and nitrogen (nitrides CrN and Cr 2 N).

Cr compounds (+2)

The oxidation state +2 corresponds to the basic oxide CrO (black). Cr 2+ salts (blue solutions) are obtained by reduction of Cr 3+ salts or dichromates with zinc in an acidic medium (“with hydrogen at the time of isolation”):

All these Cr 2+ salts are strong reducing agents to the extent that they displace hydrogen from water upon standing. Oxygen in the air, especially in an acidic environment, oxidizes Cr 2+, as a result of which the blue solution quickly turns green.

Brown or yellow hydroxide Cr (OH) 2 precipitates when alkalis are added to solutions of chromium (II) salts.

Chromium dihalides CrF 2, CrCl 2, CrBr 2 and CrI 2 were synthesized

Cr (+3) compounds

The oxidation state +3 corresponds to amphoteric oxide Cr 2 O 3 and hydroxide Cr (OH) 3 (both are green). This is the most stable oxidation state of chromium. Chromium compounds in this oxidation state have a color from dirty lilac (ion 3+) to green (anions are present in the coordination sphere).

Cr 3+ tends to form double sulfates of the type M I Cr (SO 4) 2 12H 2 O (alum)

Chromium (III) hydroxide is obtained by acting with ammonia on solutions of chromium (III) salts:

Cr + 3NH + 3H2O → Cr (OH) ↓ + 3NH

You can use solutions of alkalis, but in their excess, a soluble hydroxo complex is formed:

Cr + 3OH → Cr (OH) ↓

Cr (OH) + 3OH →

By fusing Cr 2 O 3 with alkalis, chromites are obtained:

Cr2O3 + 2NaOH → 2NaCrO2 + H2O

Uncalcined chromium (III) oxide dissolves in alkaline solutions and acids:

Cr2O3 + 6HCl → 2CrCl3 + 3H2O

When chromium (III) compounds are oxidized in an alkaline medium, chromium (VI) compounds are formed:

2Na + 3HO → 2NaCrO + 2NaOH + 8HO

The same happens when chromium (III) oxide is fused with alkali and oxidizing agents, or with alkali in air (the melt thus acquires a yellow color):

2Cr2O3 + 8NaOH + 3O2 → 4Na2CrO4 + 4H2O

Chromium compounds (+4)[

With the careful decomposition of chromium (VI) oxide CrO 3 under hydrothermal conditions, chromium (IV) oxide CrO 2 is obtained, which is ferromagnetic and has metallic conductivity.

Among chromium tetrahalides, CrF 4 is stable, chromium tetrachloride CrCl 4 exists only in vapors.

Chromium compounds (+6)

The oxidation state +6 corresponds to the acidic chromium (VI) oxide CrO 3 and a number of acids, between which there is an equilibrium. The simplest of them are chromic H 2 CrO 4 and two-chromic H 2 Cr 2 O 7. They form two series of salts: yellow chromates and orange dichromates, respectively.

Chromium oxide (VI) CrO 3 is formed by the interaction of concentrated sulfuric acid with dichromate solutions. A typical acidic oxide, when interacting with water, it forms strong unstable chromic acids: chromic H 2 CrO 4, dichromic H 2 Cr 2 O 7 and other isopolyacids with the general formula H 2 Cr n O 3n + 1. An increase in the degree of polymerization occurs with a decrease in pH, that is, an increase in acidity.