Melting chromium. Chromium is a refractory but very useful metal in construction. I. Repetition of the material of the previous lesson

And fat.

Scientists claim that cholesterol levels are affected by chromium. Element It is considered biogenic, that is, it is necessary for the body, not only for humans, but for all mammals.

With a lack of chromium, their growth slows down and cholesterol “jumps”. The norm is 6 milligrams of chromium from the total mass of a person.

Ions of the substance are found in all tissues of the body. You should be getting 9 micrograms per day.

You can take them from seafood, pearl barley, beets, liver and duck meat. While you are buying products, we will talk about other uses and properties of chromium.

Chromium Properties

Chromium is a chemical element pertaining to metals. The color of the substance is silver-blue.

The element is under the 24th ordinal, or, as they say, atomic number.

The number indicates the number of protons in the nucleus. As for the electrons revolving near it, they have special property- fail.

This means that one or two particles can move from one sublevel to another.

As a result, the 24th element is able to half fill the 3rd sublevel. This results in a stable electronic configuration.

The failure of electrons is a rare phenomenon. In addition to chromium, perhaps only,, and are remembered.

Like the 24th substance, they are chemically inactive. Not then does the atom come to a stable state in order to react with everyone in a row.

At normal conditions chromium is an element of the periodic table, which can only be "stirred up".

The latter, being the antipode of the 24th substance, is maximally active. The reaction produces fluoride chrome.

Element, properties which are discussed, does not oxidize, is not afraid of moisture and refractory materials.

The latter characteristic "delays" the reactions that are possible during heating. So, interaction with water vapor starts only at 600 degrees Celsius.

It turns out chromium oxide. The reaction with is also started, giving the nitride of the 24th element.

At 600 degrees, several compounds with and the formation of sulfide are also possible.

If you bring the temperature up to 2000, chromium will ignite on contact with oxygen. The result of combustion will be a dark green oxide.

This precipitate easily reacts with solutions and acids. The result of the interaction is chloride and chromium sulfide. All compounds of the 24th substance, as a rule, are brightly colored.

In its purest form, the main characteristics of the element chromium- toxicity. Metal dust irritates lung tissue.

Dermatitis, that is, allergic diseases, may appear. Accordingly, it is better not to exceed the norm of chromium for the body.

There is a norm for the content of the 24th element in the air. On cubic meter atmosphere should account for 0.0015 milligrams. Exceeding the standard is considered pollution.

At metallic chrome high density- more than 7 grams per cubic centimeter. This means that the substance is quite heavy.

The metal is also quite high. It depends on the electrolyte temperature and current density. In fungi and mold, this, apparently, commands respect.

If wood is impregnated with a chromium composition, microorganisms will not undertake to destroy it. Builders use it.

They are also satisfied with the fact that the treated wood burns worse, because chromium is a refractory metal. How and where else it can be applied, we will tell further.

Application of chromium

Chromium is an alloying element when smelted. Remember that under normal conditions, the 24th metal does not oxidize, does not rust?

The basis of steels -. It cannot boast of such properties. Therefore, chromium is added to increase corrosion resistance.

In addition, the addition of the 24th substance lowers the critical cooling rate point.

Silicothermal chromium is used for smelting. This is a duet of the 24th element with nickel.

Silicon, are used as additives. Nickel is responsible for ductility, while chromium is responsible for its oxidation resistance and hardness.

Connect chromium and with. It turns out superhard stellite. Additives to it - molybdenum and.

The composition is expensive, but necessary for surfacing machine parts in order to increase their wear resistance. Stellite is also sprayed onto working machines,.

In decorative corrosion-resistant coatings, as a rule, chromium compounds.

The bright range of their colors comes in handy. In cermets, color is not needed, therefore, powder chromium is used. It is added, for example, for strength to the lower layer of crowns for.

Chromium formula- component . This is a mineral from the group, but it does not have the usual color.

Uvarovite is a stone, and it is chromium that makes it so. It's no secret that they are used.

The green variety of stone is no exception, moreover, it is valued higher than the red one, because it is rare. Still, uvarovit a little standard.

This is also a plus, because mineral inserts are harder to scratch. The stone is faceted faceted, that is, forming corners, which increases the play of light.

Chromium mining

Extracting chromium from minerals is unprofitable. Most with the 24th element are used in their entirety.

In addition, the chromium content in, as a rule, is low. The substance is extracted, in the ground, from the ores.

One of them is associated opening chrome. It was found in Siberia. Crocoite was found there in the 18th century. It is red lead ore.

Its basis is, the second element is chromium. It was discovered by a German chemist named Lehman.

At the time of the discovery of the crocoite, he was visiting St. Petersburg, where he conducted experiments. Now, the 24th element is obtained by electrolysis of concentrated aqueous solutions of chromium oxide.

Electrolysis of sulfate is also possible. These are 2 ways to get the cleanest chrome. Molecule oxide or sulfate is destroyed in the crucible, where the original compounds are ignited.

The 24th element is separated, the rest goes to slag. It remains to smelt chromium in an arc. This is how the purest metal is extracted.

There are other ways to get chromium element, for example, reduction of its oxide with silicon.

But, this method gives a metal with a large amount of impurities and, moreover, is more expensive than electrolysis.

Chrome price

In 2016, the price of chromium is still declining. January began with 7450 dollars per ton.

By mid-summer, only 7,100 conventional units are asked for per 1,000 kilograms of metal. Data provided by Infogeo.ru.

That is, Russian prices are considered. The world price of chromium reached almost $9,000 per ton.

The lowest mark of summer differs from the Russian one by only 25 dollars upwards.

If not the industrial sector is considered, for example, metallurgy, but the benefits of chromium for the body, you can study the offers of pharmacies.

So, "Picolinate" of the 24th substance costs about 200 rubles. For "Kartnitin Chrome Forte" they ask for 320 rubles. This is the price tag for a pack of 30 tablets.

Turamine Chromium can also make up for the deficiency of the 24th element. Its cost is 136 rubles.

Chromium, by the way, is part of the tests for the detection of drugs, in particular, marijuana. One test costs 40-45 rubles.

Chromium is 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). The simple substance chromium is a bluish-white hard metal.

Chemical properties of chromium

Under normal conditions, chromium reacts only with fluorine. At high temperatures (above 600°C) it interacts with oxygen, halogens, nitrogen, silicon, boron, sulfur, and phosphorus.

4Cr + 3O 2 – t° →2Cr 2 O 3

2Cr + 3Cl 2 – t° → 2CrCl 3

2Cr + N 2 – t° → 2CrN

2Cr + 3S – t° → Cr 2 S 3

In a hot state, it reacts with water vapor:

2Cr + 3H 2 O → Cr 2 O 3 + 3H 2

Chromium dissolves in dilute strong acids(HCl, H2SO4)

In the absence of air, Cr 2+ salts are formed, and in air, Cr 3+ salts are formed.

Cr + 2HCl → CrCl 2 + H 2

2Cr + 6HCl + O 2 → 2CrCl 3 + 2H 2 O + H 2

The presence of a protective oxide film on the surface of the metal explains its passivity in relation to concentrated solutions of acids - oxidizing agents.

Chromium compounds

Chromium(II) oxide and chromium(II) hydroxide are basic.

Cr(OH) 2 + 2HCl → CrCl 2 + 2H 2 O

Chromium (II) compounds are strong reducing agents; pass into chromium (III) compounds under the action of atmospheric oxygen.

2CrCl 2 + 2HCl → 2CrCl 3 + H 2

4Cr(OH) 2 + O 2 + 2H 2 O → 4Cr(OH) 3

Chromium oxide (III) Cr 2 O 3 is a green, water-insoluble powder. It can be obtained by calcining chromium (III) hydroxide or potassium and ammonium dichromates:

2Cr(OH) 3 – t° → Cr 2 O 3 + 3H 2 O

4K 2 Cr 2 O 7 – t° → 2Cr 2 O 3 + 4K 2 CrO 4 + 3O 2

(NH 4) 2 Cr 2 O 7 - t ° → Cr 2 O 3 + N 2 + 4H 2 O (volcano reaction)

amphoteric oxide. When Cr 2 O 3 is fused with alkalis, soda and acid salts, chromium compounds are obtained with an oxidation state (+3):

Cr 2 O 3 + 2NaOH → 2NaCrO 2 + H 2 O

Cr 2 O 3 + Na 2 CO 3 → 2NaCrO 2 + CO 2

When fused with a mixture of alkali and an oxidizing agent, chromium compounds are obtained in the oxidation state (+6):

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

Chromium (III) hydroxide C r (OH) 3 . amphoteric hydroxide. Grey-green, decomposes on heating, losing water and forming green metahydroxide CrO(OH). Does not dissolve in water. It precipitates from solution as a gray-blue and bluish-green hydrate. Reacts with acids and alkalis, does not interact with ammonia hydrate.

It has amphoteric properties - it dissolves in both acids and alkalis:

2Cr(OH) 3 + 3H 2 SO 4 → Cr 2 (SO 4) 3 + 6H 2 O Cr(OH) 3 + ZH + = Cr 3+ + 3H 2 O

Cr (OH) 3 + KOH → K, Cr (OH) 3 + ZON - (conc.) \u003d [Cr (OH) 6] 3-

Cr (OH) 3 + KOH → KCrO 2 + 2H 2 O Cr (OH) 3 + MON \u003d MCrO 2 (green) + 2H 2 O (300-400 ° C, M \u003d Li, Na)

Cr(OH) 3 →(120 o C – H 2 O) CrO(OH) →(430-1000 0 С –H 2 O) Cr2O3

2Cr(OH) 3 + 4NaOH (conc.) + ZN 2 O 2 (conc.) \u003d 2Na 2 CrO 4 + 8H 2 0

Receipt: precipitation with ammonia hydrate from a solution of chromium(III) salts:

Cr 3+ + 3(NH 3 H 2 O) = WITHr(OH) 3 ↓+ ЗНН 4+

Cr 2 (SO 4) 3 + 6NaOH → 2Cr(OH) 3 ↓+ 3Na 2 SO 4 (in excess of alkali - the precipitate dissolves)

Salts of chromium (III) have a purple or dark green color. By chemical properties, they resemble colorless aluminum salts.

Cr(III) compounds can exhibit both oxidizing and reducing properties:

Zn + 2Cr +3 Cl 3 → 2Cr +2 Cl 2 + ZnCl 2

2Cr +3 Cl 3 + 16NaOH + 3Br 2 → 6NaBr + 6NaCl + 8H 2 O + 2Na 2 Cr +6 O 4

Hexavalent chromium compounds

Chromium(VI) oxide CrO 3 - bright red crystals, soluble in water.

Prepared from potassium chromate (or dichromate) and H 2 SO 4 (conc.).

K 2 CrO 4 + H 2 SO 4 → CrO 3 + K 2 SO 4 + H 2 O

K 2 Cr 2 O 7 + H 2 SO 4 → 2CrO 3 + K 2 SO 4 + H 2 O

CrO 3 - acidic oxide, forms yellow chromates CrO 4 2- with alkalis:

CrO 3 + 2KOH → K 2 CrO 4 + H 2 O

In an acidic environment, chromates turn into orange dichromates Cr 2 O 7 2-:

2K 2 CrO 4 + H 2 SO 4 → K 2 Cr 2 O 7 + K 2 SO 4 + H 2 O

IN alkaline environment this reaction proceeds in the opposite direction:

K 2 Cr 2 O 7 + 2KOH → 2K 2 CrO 4 + H 2 O

Potassium dichromate is an oxidizing agent in an acidic environment:

K 2 Cr 2 O 7 + 4H 2 SO 4 + 3Na 2 SO 3 \u003d Cr 2 (SO 4) 3 + 3Na 2 SO 4 + K 2 SO 4 + 4H 2 O

K 2 Cr 2 O 7 + 4H 2 SO 4 + 3NaNO 2 = Cr 2 (SO 4) 3 + 3NaNO 3 + K 2 SO 4 + 4H 2 O

K 2 Cr 2 O 7 + 7H 2 SO 4 + 6KI = Cr 2 (SO 4) 3 + 3I 2 + 4K 2 SO 4 + 7H 2 O

K 2 Cr 2 O 7 + 7H 2 SO 4 + 6FeSO 4 = Cr 2 (SO 4) 3 + 3Fe 2 (SO 4) 3 + K 2 SO 4 + 7H 2 O

Potassium chromate K 2 Cr About 4 . Oksosol. Yellow, non-hygroscopic. Melts without decomposition, thermally stable. Highly soluble in water yellow the color of the solution corresponds to the CrO 4 2- ion, slightly hydrolyzes the anion. In an acidic environment, it passes into K 2 Cr 2 O 7. Oxidizing agent (weaker than K 2 Cr 2 O 7). Enters into ion exchange reactions.

Qualitative reaction on the ion CrO 4 2- - precipitation of a yellow precipitate of barium chromate, decomposing in a strongly acidic environment. It is used as a mordant for dyeing fabrics, a leather tanning agent, a selective oxidizing agent, a reagent in analytical chemistry.

Equations of the most important reactions:

2K 2 CrO 4 + H 2 SO 4 (30%) = K 2 Cr 2 O 7 + K 2 SO 4 + H 2 O

2K 2 CrO 4 (t) + 16HCl (conc., horizon) \u003d 2CrCl 3 + 3Cl 2 + 8H 2 O + 4KCl

2K 2 CrO 4 +2H 2 O+3H 2 S=2Cr(OH) 3 ↓+3S↓+4KOH

2K 2 CrO 4 +8H 2 O+3K 2 S=2K[Сr(OH) 6]+3S↓+4KOH

2K 2 CrO 4 + 2AgNO 3 \u003d KNO 3 + Ag 2 CrO 4 (red) ↓

Qualitative response:

K 2 CrO 4 + BaCl 2 \u003d 2KSl + BaCrO 4 ↓

2ВаСrO 4 (t) + 2НCl (razb.) = ВаСr 2 O 7(p) + ВаС1 2 + Н 2 O

Receipt: sintering of chromite with potash in air:

4(Cr 2 Fe ‖‖)O 4 + 8K 2 CO 3 + 7O 2 = 8K 2 CrO 4 + 2Fe 2 O 3 + 8СO 2 (1000 °С)

Potassium dichromate K 2 Cr 2 O 7 . Oksosol. technical name chrompeak. Orange-red, non-hygroscopic. Melts without decomposition, decomposes on further heating. Highly soluble in water orange the color of the solution corresponds to the ion Cr 2 O 7 2-). In an alkaline medium, it forms K 2 CrO 4 . A typical oxidizing agent in solution and when fused. Enters into ion exchange reactions.

Qualitative reactions- blue coloring of the ether solution in the presence of H 2 O 2, blue coloring aqueous solution under the action of atomic hydrogen.

It is used as a leather tanning agent, a mordant for dyeing fabrics, a component of pyrotechnic compositions, a reagent in analytical chemistry, a metal corrosion inhibitor, mixed with H 2 SO 4 (conc.) - for washing chemical dishes.

Equations of the most important reactions:

4K 2 Cr 2 O 7 \u003d 4K 2 CrO 4 + 2Cr 2 O 3 + 3O 2 (500-600 o C)

K 2 Cr 2 O 7 (t) + 14HCl (conc) \u003d 2CrCl 3 + 3Cl 2 + 7H 2 O + 2KCl (boiling)

K 2 Cr 2 O 7 (t) + 2H 2 SO 4 (96%) ⇌2KHSO 4 + 2CrO 3 + H 2 O (“chromium mixture”)

K 2 Cr 2 O 7 +KOH (conc) \u003d H 2 O + 2K 2 CrO 4

Cr 2 O 7 2- + 14H + + 6I - \u003d 2Cr 3+ + 3I 2 ↓ + 7H 2 O

Cr 2 O 7 2- + 2H + + 3SO 2 (g) \u003d 2Cr 3+ + 3SO 4 2- + H 2 O

Cr 2 O 7 2- + H 2 O + 3H 2 S (g) \u003d 3S ↓ + 2OH - + 2Cr 2 (OH) 3 ↓

Cr 2 O 7 2- (conc) + 2Ag + (razb.) \u003d Ag 2 Cr 2 O 7 (so red) ↓

Cr 2 O 7 2- (razb.) + H 2 O + Pb 2+ \u003d 2H + + 2PbCrO 4 (red) ↓

K 2 Cr 2 O 7 (t) + 6HCl + 8H 0 (Zn) \u003d 2CrCl 2 (syn) + 7H 2 O + 2KCl

Receipt: treatment of K 2 CrO 4 with sulfuric acid:

2K 2 CrO 4 + H 2 SO 4 (30%) = K 2Cr 2 O 7 + K 2 SO 4 + H 2 O

Chromium is a refractory, very hard metal with extraordinary resistance to corrosion. These unique qualities provided him with such a high demand in industry and construction.

The consumer is most often familiar not with chrome products, but with objects coated with a thin layer of metal. The dazzling mirror shine of such a coating is attractive in itself, but it also has a purely practical significance. Chrome is resistant to corrosion and is able to protect alloys and metals from rust.

And today we will answer questions about whether chromium is a metal or non-metal, and if it is a metal, then which one: black or non-ferrous, heavy or light. We will also tell you in what form chromium occurs in nature, and what are the differences between chromium and other similar metals.

To begin with, let's talk about what chromium looks like, what metals it contains, and what is the peculiarity of such a substance. Chromium is a typical silver-bluish metal, heavy, exceeds in density, and also belongs to the category of refractory - its melting and boiling points are very high.

The element chromium is placed in the secondary subgroup of the 6th group in the 4th period. It is close in properties to molybdenum and tungsten, although it also has noticeable differences. The latter usually show only the highest degree oxidation, while chromium exhibits a valency of two, and three, and six. This means that the element forms many different compounds.

It was the compounds that gave the name to the element itself - from the Greek paint, color. The fact is that its salts and oxides are painted in a wide variety of bright colors.

This video will tell you what chrome is:

Features and differences compared to other metals

In the study of metal, two properties of a substance aroused the greatest interest: hardness and refractoriness. Chromium is one of the hardest metals - it ranks fifth and is inferior to uranium, iridium, tungsten and beryllium. However, this quality turned out to be unclaimed, since the metal had properties that were more important for industry.

Chromium melts at 1907 C. It is inferior to tungsten or molybdenum in this indicator, but still belongs to refractory substances. True, impurities strongly influence its melting point.

Like many corrosion-resistant metals, chromium forms a thin and very dense oxide film in air. The latter covers the access of oxygen, nitrogen and moisture to the substance, which makes it invulnerable. The peculiarity is that he transfers this quality to his alloy with: in the presence of an element, the potential of the a-phase of iron increases and, as a result, the steel in air is also covered with a dense oxide film. This is the secret to the durability of stainless steel.
Being a refractory substance, the metal also increases the melting point of the alloy. Heat-resistant and heat-resistant steels necessarily include a proportion of chromium, and sometimes very large - up to 60%. The addition of both and chromium has an even stronger effect.
Chromium forms alloys with its brothers in the group - molybdenum and tungsten. They are used for coating parts where particularly high wear resistance at high temperatures is required.

The advantages and disadvantages of chromium are described below.

Chrome as metal (photo)

Advantages

Like any other substance, metal has its advantages and disadvantages, and their combination determines its use.

An unconditional plus of the substance is corrosion resistance and the ability to transfer this property to its alloys. Chrome stainless steels are of great importance because they decided at once whole line problems in the construction of ships, submarines, building frames and so on.
Corrosion resistance is provided in another way - they cover the object with a thin layer of metal. The popularity of this method is very high, today there are at least a dozen ways of chrome plating in different conditions and to obtain different results.
The chromium layer creates a bright mirror shine, so chrome plating is used not only to protect the alloy from corrosion, but also to obtain an aesthetic appearance. Moreover, modern chromium plating methods make it possible to create a coating on any material - not only on metal, but also on plastic and ceramics.
Obtaining heat-resistant steel with the addition of chromium should also be attributed to the advantages of the substance. There are many areas where metal parts must work at high temperatures, and iron itself does not have such resistance to stress at temperature.
Of all the refractory substances, it is the most resistant to acids and bases.
The advantage of the substance can be considered its prevalence - 0.02% in earth's crust, and a relatively simple way to mine and obtain. Of course, it requires energy consumption, but it cannot be compared with a complex one, for example.

Flaws

The disadvantages include qualities that do not allow full use of all the properties of chromium.

First of all, this is a strong dependence of physical, and not only chemical properties from impurities. Even the melting point of the metal was difficult to establish, since in the presence of an insignificant fraction of nitrogen or carbon, the indicator changed noticeably.
Despite the higher electrical conductivity compared to, chromium is much less used in electrical engineering and its cost is quite high. It is much more difficult to make something from it: the high melting point and hardness significantly limit the application.
Pure chromium is a malleable metal, containing impurities becomes very hard. To obtain at least a relatively ductile metal, it has to be subjected to additional processing, which, of course, increases the cost of manufacturing.

metal structure

The chromium crystal has a body-centered cubic lattice, a=0.28845 nm. Above a temperature of 1830 C, a modification with a face-centered cubic lattice can be obtained.

At a temperature of +38 C, a second-order phase transition is recorded with an increase in volume. In this case, the crystal lattice of the substance does not change, but its magnetic properties become completely different. Up to this temperature - the Neel point, chromium exhibits the properties of an antiferromagnet, that is, it is a substance that is almost impossible to magnetize. Above the Neel point, the metal becomes a typical paramagnet, that is, it exhibits magnetic properties in the presence of a magnetic field.

Properties and characteristics

IN normal conditions the metal is quite inert - both thanks to the oxide film and simply by its nature. However, when the temperature rises, it reacts with simple substances, and with acids, and with bases. Its compounds are very diverse and are used very widely. physical characteristics metals, as mentioned, strongly depend on the amount of impurities. In practice, they deal with chromium with a purity of up to 99.5%. are:

melting temperature- 1907 C. This value serves as the boundary between refractory and ordinary substances;
boiling temperature- 2671 C;
Mohs hardness – 5;
electrical conductivity– 9 106 1/(Ohm m). According to this indicator, chromium is second only to silver and gold;
resistivity–127 (Ohm mm2)/m;
thermal conductivity substances is 93.7 W / (m K);
specific heat–45 J/(g K).

The thermophysical characteristics of the substance are somewhat anomalous. At the Neel point, where the volume of the metal changes, its coefficient of thermal expansion sharply increases and continues to grow with increasing temperature. The thermal conductivity also behaves abnormally - it drops at the Neel point and decreases when heated.

The element is among the necessary: in the human body, chromium ions are participants in carbohydrate metabolism and the process of regulating insulin release. The daily dose is 50-200 mcg.

Chromium is non-toxic, although in the form of a metal powder it can cause irritation to the mucous membranes. Its trivalent compounds are also relatively safe and are even used in the food and sports industries. But hexavalent for humans are poison, cause severe damage to the respiratory tract and gastrointestinal tract.

We will talk further about the production and price of chromium metal per kg today.

This video will show if the finish is chrome:

Production

In a large number of different minerals - often accompanies and. However, its content is insufficient to be of industrial importance. Only rocks containing at least 40% of the element are promising, so there are few minerals suitable for extraction, mainly chromium iron ore or chromite.

The mineral is mined by the mine and quarry method, depending on the depth of occurrence. And since the ore initially contains a large proportion of the metal, it is almost never enriched, which, accordingly, simplifies and reduces the cost of the production process.

About 70% of the mined metal is used for alloying steel. Moreover, it is often used not in its pure form, but in the form of ferrochrome. The latter can be obtained directly in a shaft electric furnace or a blast furnace - this is how carbon ferrochromium is obtained. If a low carbon compound is required, the aluminothermic method is used.

This method produces both pure chromium and ferrochrome. To do this, a charge is loaded into the smelting shaft, including chromium iron ore, chromium oxide, sodium nitrate and. The first portion, the ignition mixture, is ignited, and the rest of the charge is loaded into the melt. At the end, a flux is added - lime, to facilitate the extraction of chromium. Melting takes about 20 minutes. After some cooling, the shaft is tilted, slag is released, returned to its original position and tilted again, now both chromium and slag are removed into the mold. After cooling, the resulting block is separated.
Another method is also used - metallothermic melting. It is carried out in an electric furnace in a rotating shaft. The charge here is divided into 3 parts, each differs in composition. This method allows you to extract large quantity chromium, but, most importantly, reduces consumption.
If it is required to obtain a chemically pure metal, they resort to a laboratory method: crystals are planted by electrolysis of chromate solutions.

The cost of chromium metal per 1 kg fluctuates markedly, since it depends on the volume of rolled metal produced - the main consumer of the element. In January 2017, 1 ton of metal was valued at $7,655.

Application

Chrome plating

Chrome plating can be divided into 2 categories:

functional- its purpose is to prevent corrosion of the product. The layer thickness is greater here, so the chrome plating process takes longer - sometimes up to 24 hours. In addition to the fact that the chromium layer will prevent rusting, it significantly increases the wear resistance of the part;
decorative- Chrome creates a mirror-shiny surface. Car enthusiasts and motorcycle racers rarely turn down the opportunity to decorate their car with chrome parts. The decorative coating layer is much thinner - up to 0.0005 mm.

Chrome plating is actively used in modern construction and in the manufacture of furniture. Mirrored fittings, bathroom and kitchen accessories, kitchen utensils, furniture parts - chrome-plated products are extremely popular. And since thanks to modern method chromium plating, a coating can be created literally on any object, and somewhat atypical methods of application have appeared. So, for example, chrome-plated plumbing cannot be attributed to trivial solutions.

Chromium is a metal with very unusual properties, and its qualities are in demand in industry. For the most part, its alloys and compounds are of interest, which only increases the importance of the metal for the national economy.

The video below will tell about the removal of chrome from metal:

DEFINITION

Chromium- twenty-fourth element Periodic table. Designation - Cr from the Latin "chromium". Located in the fourth period, VIB group. Refers to metals. The core charge is 24.

Chromium is contained in the earth's crust in an amount of 0.02% (wt.). In nature, it occurs mainly in the form of iron chromium FeO×Cr 2 O 3 .

Chromium is a solid shiny metal (Fig. 1), melting at 1890 o C; its density is 7.19 g / cm 3. At room temperature, chromium is resistant to both water and air. Dilute sulfuric and hydrochloric acids dissolve chromium, releasing hydrogen. in cold concentrated nitric acid chromium is insoluble and becomes passive after treatment with it.

Rice. 1. Chrome. Appearance.

Atomic and molecular weight of chromium

DEFINITION

Relative molecular weight of a substance(M r) is a number showing how many times the mass of a given molecule is greater than 1/12 of the mass of a carbon atom, and relative atomic mass of an element(A r) - how many times the average mass of atoms chemical element more than 1/12 of the mass of a carbon atom.

Since chromium exists in the free state in the form of monatomic Cr molecules, the values of its atomic and molecular masses are the same. They are equal to 51.9962.

Isotopes of chromium

It is known that chromium can occur in nature in the form of four stable isotopes 50Cr, 52Cr, 53Cr, and 54Cr. Their mass numbers are 50, 52, 53, and 54, respectively. The nucleus of the atom of the chromium isotope 50 Cr contains twenty-four protons and twenty-six neutrons, and the remaining isotopes differ from it only in the number of neutrons.

There are artificial isotopes of chromium with mass numbers from 42 to 67, among which the most stable is 59 Cr with a half-life of 42.3 minutes, as well as one nuclear isotope.

Chromium ions

On the outer energy level of the chromium atom, there are six electrons that are valence:

1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 4s 1 .

As a result of chemical interaction, chromium gives up its valence electrons, i.e. is their donor, and turns into a positively charged ion:

Cr 0 -2e → Cr 2+;

Cr 0 -3e → Cr 3+;

Cr 0 -6e → Cr 6+.

Molecule and atom of chromium

In the free state, chromium exists in the form of monatomic Cr molecules. Here are some properties that characterize the atom and molecule of chromium:

Chromium alloys

Chromium metal is used for chromium plating, and also as one of the most important components of alloy steels. The introduction of chromium into steel increases its resistance to corrosion both in aqueous media at ordinary temperatures and in gases at elevated temperatures. In addition, chromium steels have increased hardness. Chromium is a part of stainless acid-resistant, heat-resistant steels.

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

Exercise

Chromium oxide (VI) weighing 2 g was dissolved in water weighing 500 g. Calculate the mass fraction of chromic acid H 2 CrO 4 in the resulting solution.

Solution

Let's write the reaction equation for obtaining chromic acid from chromium (VI) oxide:

CrO 3 + H 2 O \u003d H 2 CrO 4.

Find the mass of the solution:

m solution \u003d m (CrO 3) + m (H 2 O) \u003d 2 + 500 \u003d 502 g.

n (CrO 3) \u003d m (CrO 3) / M (CrO 3);

n (CrO 3) \u003d 2/100 \u003d 0.02 mol.

According to the reaction equation n(CrO 3) :n(H 2 CrO 4) = 1:1, then

n (CrO 3) \u003d n (H 2 CrO 4) \u003d 0.02 mol.

Then the mass of chromic acid will be equal to ( molar mass- 118 g/mol):

m (H 2 CrO 4) \u003d n (H 2 CrO 4) × M (H 2 CrO 4);

m (H 2 CrO 4) \u003d 0.02 × 118 \u003d 2.36 g.

The mass fraction of chromic acid in solution is:

ω = msolute / msolution × 100%;

ω (H 2 CrO 4) \u003d m solute (H 2 CrO 4) / m solution × 100%;

ω (H 2 CrO 4) \u003d 2.36 / 502 × 100% \u003d 0.47%.

Answer

The mass fraction of chromic acid is 0.47%.

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 are used in paints and pigments. The red color of a 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) for cleaning laboratory glassware. In addition, chromium oxide (VI) 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 named it "Siberian red lead". Although it was erroneously 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 croconte mineral.

In 1770, Peter Simon Pallas visited the place where Leman found a red lead mineral that had very useful pigment properties in paints. The use of Siberian red lead as a paint fast development. In addition, bright yellow from croconte has become fashionable.

In 1797, Nicolas-Louis Vauquelin obtained samples of red By mixing croconte with hydrochloric acid he received the oxide CrO 3 . Chromium as a chemical element was isolated in 1798. Vauquelin obtained it by heating oxide with charcoal. He was also able to detect traces of chromium in gemstones 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 is used in the 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", because of the many colored compounds that can be obtained from it.

Mining and production

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

Deposits of native chromium metal 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 helped form pure chromium and diamonds.

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

In 2000, approximately 15 Mt of chromite ore was mined and processed into 4 Mt of ferrochromium, 70% chromium-iron, with an estimated 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. Included in the VI group. It melts at a temperature of 1907 °C. In the presence of oxygen, chromium quickly forms a thin layer of oxide, which protects the metal from further interaction with oxygen.

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

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

isotopes

Isotopes of chromium have atomic weights from 43 to 67. Typically, this chemical element consists of three stable forms: 52 Cr, 53 Cr and 54 Cr. Of these, 52 Cr is the most common (83.8% of all natural chromium). In addition, 19 radioisotopes have been described, of which 50 Cr is the most stable, with a half-life exceeding 1.8 x 10 17 years. 51 Cr has a half-life of 27.7 days, and for all other radioactive isotopes it does not exceed 24 hours, and for most of them it lasts less than one minute. The element also has two metastates.

Chromium isotopes in the earth's crust, as a rule, accompany manganese isotopes, which finds application in geology. 53 Cr is formed during the radioactive decay of 53 Mn. The Mn/Cr isotope ratio reinforces other information about early history solar system. Changes in the ratios of 53 Cr/ 52 Cr and Mn/Cr 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 oxide (III) 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. The oxide can dissolve in acids, forming salts, and in molten alkali, chromites.

Potassium bichromate

K 2 Cr 2 O 7 is a powerful oxidizing agent and is preferred as a cleaning agent for 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 process of oxidation of organic compounds, converting primary alcohol into aldehyde, and then into carbon dioxide.

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

Chromic acid

The compound has the hypothetical structure H 2 CrO 4 . Neither chromic nor dichromic acids are found in nature, but their anions are found in various substances. "Chromic acid", which can be found on sale, is actually its acid anhydride - CrO 3 trioxide.

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 under the name "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 whose properties have provided it with many different uses, some of which are listed below.

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

Chromium is a catalyst for various reactions. It is used to make molds for firing bricks. Its salts tan the skin. Potassium bichromate is used to oxidize organic compounds such as alcohols and aldehydes, as well as to clean laboratory glassware. It serves as a fixing agent for dyeing fabric and is also used in photography and photo printing.

CrO 3 is used to make magnetic tapes (for example, for audio recording), which have better characteristics than iron oxide films.

Role in biology

Trivalent chromium is a chemical element essential 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 not generally 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. With chronic exposure, chromium(VI) compounds can cause eye damage if not properly treated. In addition, it is 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 allowable concentration of Cr (VI) in drinking water is 0.05 mg per litre.

Because chromium compounds are used in dyes and leather tanning, they are often found in the soil and groundwater of abandoned industrial sites that require environmental cleanup and remediation. Primer containing Cr(VI) is still widely used in the aerospace and automotive industries.

Element properties

Main physical properties chrome 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 .

Chemical properties of chromium

Chromium compounds

Features and differences compared to other metals

Advantages

Flaws

metal structure

Properties and characteristics

Production

Application

Categories

Chrome plating

Atomic and molecular weight of chromium

Isotopes of chromium

Chromium ions

Molecule and atom of chromium

Chromium alloys

Examples of problem solving

Discovery and etymology

Mining and production

Main characteristics

isotopes

Chemical element chromium: properties, formula of compounds

Potassium bichromate

Chromic acid

Lead(II) chromate

Cr and pentavalent bond

Application

Role in biology

Precautionary measures

Element properties

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