ChemicalBook CAS DataBase List 7440-47-3

7440-47-3

Name	Chromium
CAS	7440-47-3
EINECS(EC#)	231-157-5
Molecular Formula	Cr
MDL Number	MFCD00010944
Molecular Weight	52
MOL File	7440-47-3.mol

Chemical Properties

Appearance	Chromium may exist in one of three valence states in compounds, , , and . The most stable oxidation state is trivalent chromium; Hexavalent chromium is a less stable state. Chromium (element) blue-white to steel-gray, lustrous, brittle, hard, odorless solid. Elemental:
Melting point	1857 °C (lit.)
Boiling point	2672 °C (lit.)
density	7.14 g/mL at 25 °C(lit.)
Fp	50 °F
storage temp.	no restrictions.
solubility	reacts with dilute acid solutions
form	powder
color	Silver-gray
Specific Gravity	7.2
Odor	Odorless
PH	<1 (H2O, 20°C)
Stability:	Stable. Incompatible with carbonates, strong bases, mineral acids, lithium, sulfur dioxide, strong acids.
Resistivity	12.7 μΩ-cm, 20°C
Water Solubility	Insoluble in water.
Merck	13,2252
Exposure limits	TLV-TWA: chromium metal 0.5 mg/m³ (ACGIH and MSHA), 1 mg/m³ (OSHA); Cr(II) and Cr(III) compounds 0.5 mg/m³ (ACGIH); Cr(VI) compounds, water soluble and certain water insoluble, 0.05 mg/m³ (ACGIH).
History	Chromium was discovered in 1797 by Vauquelin, who prepared the metal the next year, chromium is a steel-gray, lustrous, hard metal that takes a high polish. The principal ore is chromite (FeCr2O4), which is found in Zimbabwe, Russia, South Africa, Turkey, Iran, Albania, Finland, Democratic Republic of Madagascar, the Philippines, and elsewhere. The U.S. has no appreciable chromite ore reserves. Chromium is usually produced by reducing the oxide with aluminum. Chromium is used to harden steel, to manufacture stainless steel, and to form many useful alloys. Much is used in plating to produce a hard, beautiful surface and to prevent corrosion. Chromium is used to give glass an emerald green color. It finds wide use as a catalyst. All compounds of chromium are colored; the most important are the chromates of sodium and potassium (K2CrO4) and the dichromates (K2Cr2O7) and the potassium and ammonium chrome alums, as KCr(SO4)2·12H2O. The dichromates are used as oxidizing agents in quantitative analysis, also in tanning leather. Other compounds are of industrial value; lead chromate is chrome yellow, a valued pigment. Chromium compounds are used in the textile industry as mordants, and by the aircraft and other industries for anodizing aluminum. The refractory industry has found chromite useful for forming bricks and shapes, as it has a high melting point, moderate thermal expansion, and stability of crystalline structure. Chromium is an essential trace element for human health. Many chromium compounds, however, are acutely or chronically toxic, and some are carcinogenic. They should be handled with proper safeguards. Natural chromium contains four isotopes. Twenty other isotopes are known. Chromium metal (99.95%) costs about $1000/kg. Commercial grade chromium (99%) costs about $75/kg.
CAS DataBase Reference	7440-47-3(CAS DataBase Reference)
IARC	3 (Vol. Sup 7, 49) 1990
NIST Chemistry Reference	Chromium(7440-47-3)
EPA Substance Registry System	7440-47-3(EPA Substance)

Safety Data

Hazard Codes	F,C,Xn
Risk Statements	R11:Highly Flammable. R20/21/22:Harmful by inhalation, in contact with skin and if swallowed . R34:Causes burns. R40:Limited evidence of a carcinogenic effect. R23:Toxic by inhalation. less more
Safety Statements	S16:Keep away from sources of ignition-No smoking . S26:In case of contact with eyes, rinse immediately with plenty of water and seek medical advice . S36/37/39:Wear suitable protective clothing, gloves and eye/face protection . S45:In case of accident or if you feel unwell, seek medical advice immediately (show label where possible) . S36/37:Wear suitable protective clothing and gloves . S27:Take off immediately all contaminated clothing . less more
RIDADR	UN 2924 3/PG 2
WGK Germany	3
RTECS	GB4200000
Autoignition Temperature	580°C
TSCA	Yes
HS Code	8112 21 90
HazardClass	4.1
PackingGroup	III
Hazardous Substances Data	7440-47-3(Hazardous Substances Data)
IDLA	250 mg Cr/m3

Raw materials And Preparation Products

Hazard Information

General Description

Very hard gray solid with a metallic luster.

Reactivity Profile

CHROMIUM(7440-47-3) reacts violently with NH4NO3, N2O2, Li, NO, KClO3, SO2 . Metal dusts when suspended in atmospheres of carbon dioxide may ignite and explode.

Air & Water Reactions

May be pyrophoric, as dust. Insoluble in water.

Hazard

Hexavalent chromium compounds are questionable carcinogens and corrosive on tissue, resulting in ulcers and dermatitis on prolonged contact.

Potential Exposure

Chromium metal is used in stainless and other alloy steels to impart resistance to corrosion, oxidation, and for greatly increasing the durability of metals; for chrome plating of other metals.

Fire Hazard

Non-combustible, substance itself does not burn but may decompose upon heating to produce corrosive and/or toxic fumes. Some are oxidizers and may ignite combustibles (wood, paper, oil, clothing, etc.). Contact with metals may evolve flammable hydrogen gas. Containers may explode when heated.

First aid

Move victim to fresh air. Call 911 or emergency medical service. Give artificial respiration if victim is not breathing. Do not use mouth-to-mouth method if victim ingested or inhaled the substance; give artificial respiration with the aid of a pocket mask equipped with a one-way valve or other proper respiratory medical device. Administer oxygen if breathing is difficult. Remove and isolate contaminated clothing and shoes. In case of contact with substance, immediately flush skin or eyes with running water for at least 20 minutes. For minor skin contact, avoid spreading material on unaffected skin. Keep victim warm and quiet. Effects of exposure (inhalation, ingestion, or skin contact) to substance may be delayed. Ensure that medical personnel are aware of the material(s) involved and take precautions to protect themselves. Medical observation is recommended for 24 to 48 hours after breathing overexposure, as pulmonary edema may be delayed. As first aid for pulmonary edema, a doctor or authorized paramedic may consider administering a drug or other inhalation therapy.

Shipping

UN3089 Metal powders, flammable, n.o.s., Hazard Class: 4.1; Labels: 4.1-Flammable solid. UN1759 Corrosive solids, n.o.s., Hazard class: 8; Labels: 8-Corrosive material, Technical Name required

Incompatibilities

Dust may be pyrophoric in air. Chromium metal (especially in finely divided or powder form) and insoluble salts reacts violently with strong oxidants, such as hydrogen peroxide, causing fire and explosion hazard. Reacts with diluted hydrochloric and sulfuric acids. Incompatible with alkalis and alkali carbonates

Description

Chromium as a metallic element was first discovered over 200 years ago, in 1797. But the history of chromium really began several decades before this. In 1761, in the Beresof Mines of the Ural Mountains, Johann Gottlob Lehmann obtained samples of an orange-red mineral, which he called ‘Siberian red lead.’ He analyzed this mineral in 1766 and discovered that it contained lead “mineralized with a selenitic spar and iron particles.” The mineral he found was crocoite, a lead chromate (PbCrO4).

Waste Disposal

Recovery and recycling is a viable alternative to disposal for chromium in plating wastes; tannery wastes; cooling tower blowdown water and chemical plant wastes.

Isotopes

There are 26 isotopes of the element chromium; four are stable and foundin nature, and the rest are artificially produced with half-lives from a few microsecondsto a few days. The four stable isotopes and their percentage of contribution to thetotal amount of chromium on Earth are as follows: ⁵⁰Cr = 4.345%, ⁵²Cr = 83.789%,⁵³Cr = 9.501%, and ⁵⁴Cr = 2.365%. Cr-50 is radioactive but has such a long halflife—1.8×10⁺¹⁷ years—that it is considered to contribute about 4% to the total amount ofchromium found on Earth.

Origin of Name

From the Greek word chroma or chromos, meaning “color,” because of the many colors of its minerals and compounds.

Occurrence

Chromium is the 21st most common element found in the Earth’s crust, and chromiumoxide (Cr₂O₃) is the 10th most abundant of the oxide compounds found on Earth. It is notfound in a free metallic state.The first source of chromium was found in the mineral crocoite. Today it is obtained fromthe mineral chromite (FeCr₂O₄), which is found in Cuba, Zimbabwe, South Africa, Turkey,Russia, and the Philippines. Chromite is an ordinary blackish substance that was ignored formany years. There are different grades and forms of chromium ores and compounds, based onthe classification of use of the element. Most oxides of chromium are found mixed with othermetals, such as iron, magnesium, or aluminum.Astronauts found that the moon’s basalt rocks contain several times more chromium thanis found in basalt rocks of Earth.

Characteristics

Chromium is a hard, brittle metal that, with difficulty, can be forged, rolled, and drawn,unless it is in a very pure form, in which case the chromium is easier to work with. It is anexcellent alloying metal with iron. Its bright, silvery property makes it an appropriate metal toprovide a reflective, non-corrosive attractive finish for electroplating.Various compounds of chromium exhibit vivid colors, such as red, chrome green, andchromate yellow, all used as pigments.

Uses

Chromium is used in the manufacture ofits alloys, such as chrome-steel or chromenickel-steel. It is also used for chromeplatingof other metals, for tanning leather,and in catalysts. It occurs in chromite ores(FeO·Cr2O3).

Uses

In manufacture of chrome-steel or chrome-nickel-steel alloys (stainless steel), nonferrous alloys, heat resistant bricks for refractory furnaces. To greatly increase strength, hardness and resistance of metals to abrasion, corrosion and oxidation. For chrome plating of other metals; leather tanning; as pigment and mordant; wood preservative. Use of 51Cr as diagnostic aid see sodium chromate(VI).

Uses

The best-known use of chromium is for the plating of metal and plastic parts to producea shiny, reflective finish on automobile trim, household appliances, and other items where abright finish is considered attractive. It also protects iron and steel from corrosion.It is used to make alloys, especially stainless steel for cookware, and items for whichstrength and protection from rusting and high heat are important.Its compounds are used for high-temperature electrical equipment, for tanning leather, asa mordant (fixes the dyes in textiles so that they will not run), and as an antichalking agentfor paints.Some research has shown that, even though most chromium compounds are toxic, a smalltrace of chromium is important for a healthy diet for humans. A deficiency produces diabeteslike symptoms, which can be treated with a diet of whole-grain cereal, liver, and brewer’s yeast.Chromium’s most important radioisotope is chromium-51, which has a half-life of about27 days. It is used as a radioisotope tracer to check the rate of blood flowing in constrictedarteries.Some chromium compounds (e.g., chromium chloride, chromic hydroxide, chromic phosphate) are used as catalysts for organic chemical reactions.In 1960 the first ruby laser was made from a ruby crystal of aluminum oxide (Al₂O₃). Thesecrystals contain only a small amount of chromium, which stores the energy and is responsiblefor the laser action. A small amount of chromium found in the mineral corundum is responsible for the bright red color of the ruby gemstone.

Definition

chromium: Symbol Cr. A hard silverytransition element; a.n. 24;r.a.m. 52.00; r.d. 7.19; m.p. 1857°C;b.p. 2672°C. The main ore ischromite (FeCr₂O₄). The metal has abody-centred-cubic structure. It is extractedby heating chromite withsodium chromate, from whichchromium can be obtained by electrolysis.Alternatively, chromite can be heated with carbon in an electricfurnace to give ferrochrome, whichis used in making alloy steels. Themetal is also used as a shiny decorativeelectroplated coating and in themanufacture of certain chromiumcompounds.
At normal temperatures the metalis corrosion-resistant. It reacts withdilute hydrochloric and sulphuricacids to give chromium(II) salts.These readily oxidize to the more stablechromium(III) salts. Chromiumalso forms compounds with the +6oxidation state, as in chromates,which contain the CrO4^2- ion. The elementwas discovered in 1797 byVauquelin.

Production Methods

Chromium metal is prepared by reducing the ore in a blast furnace with carbon (coke) or silicon to form an alloy of chromium and iron called ferrochrome, which is used as the starting material for the many iron-containing alloys that employ chromium. Chromium to be used in iron-free alloys is obtained by reduction or electrolysis of chromium compounds.Chromiumisdif?culttoworkinthepuremetalform; it is brittle at low temperatures, and its high melting point makes it dif?cult to cast.

Health Hazard

The toxicity of chromium alloys and compoundsvaries significantly. Chromium metaldoes not exhibit toxicity. Divalent and trivalentcompounds of chromium have a loworder of toxicity. Exposure to the dusts ofchromite or ferrochrome alloys may causelung diseases, including pneumoconiosis andpulmonary fibrosis.
Among all chromium compounds onlythe hexavalent salts are a prime health hazard.Cr⁶⁺ is more readily taken up bycells, than any other valence state of themetal. Occupational exposure to these compoundscan produce skin ulceration, dermatitis,perforation of the nasal septa, and kidneydamage. It can induce hypersensitivityreactions of the skin and renal tubular necrosis.Examples of hexavalent salts are thechromates and dichromates of sodium, potassium,and other metals. The water-solublehexavalent chromium salts are absorbed intothe bloodstream through inhalation. Manychromium(VI) compounds are carcinogenic,causing lung cancers in animals and humans.The carcinogenicity may be attributed tointracellular conversion of Cr⁶⁺ to Cr³⁺,which is biologically more active. The trivalentCr³⁺ ion can bind with nucleic acid andthus initiate carcinogenesis.
Paustenbach et al. (1996) reported a casestudy on the uptake and elimination ofCr(VI) in drinking water on a male volunteerwho ingested 2 L/day of water containing2 mg/L Cr(VI) for 17 consecutivedays. The total chromium was measured inurine, plasma and red blood cells. The eliminationhalf-life in plasma was 36 hoursand the bioavailability was estimated as 2%.The steady-state chromium concentrations inurine and blood were achieved after sevendays of Cr(VI) ingestion. This study furthermorerevealed that Cr(VI) in drinkingwater at concentrations below 10 mg/L couldbe completely reduced to Cr(III) prior tosystemic distribution. In a follow-up study,Kergen et al. (1997) examined the magnitudeof absorption, distribution and excretionof Cr(VI) in drinking water in human volunteersfollowing oral exposures to singleand repeated doses at 5 and 10 mg Cr(VI)/L.The data obtained from this study indicatedthat virtually all (> 99.7%) of the ingestedCr(VI) was reduced to Cr(III) before enteringthe blood stream. No toxicity was observed.The endogenous reducing agents within theupper GI tract and the blood were attributedto reduce hexavalent chromium into its trivalentstate and, thus, prevented any systemicuptake of Cr(VI). Such reduction appearedto be effective even under the fasting conditions.
Wise et al. (2002) investigated the cytotoxicityand clastogenicity of both water-insolubleand water-soluble Cr(VI) compounds in primaryhuman bronchial fibroblasts and foundthat they were overall cytotoxic and genotoxicto human lung cells. Although the genotoxicmechanisms of both may be mediated bysoluble Cr(VI) ions the water-insoluble saltsapparently are the potent carcinogens comparedto the water-soluble salts (Wise et al.2004). Exposure to Cr(VI) enhanced the bindingof polycyclic aromatic hydrocarbons toDNA in human lung cells (Feng et al. 2003).Hexavalent chromium has been found to besynergistic to benzo a pyrene diol epoxide onmutagenesis and cell transformation.
The catalytic effect of iron on enhancingthe rate of reduction of Cr(VI) byhuman microsomes has been reported earlier(Myers and Myers 1998). Various formsof exogenous iron markedly enhanced bothliver and lung microsomal rates of Cr(VI)reduction. Small increases in intracellulariron have shown to cause large increases inin the rate and extent of Cr(VI) reduction.Thus, individuals exposed simultaneously toCr(VI) and agents that may increase intracellulariron could, therefore, be at potentiallygreater risk for toxicity and carcinogenicityof Cr(VI).

Industrial uses

An elementary metal, chromium (symbol Cr)is used in stainless steels, heat-resistant alloys,high-strength alloy steels, electrical-resistancealloys, wear-resistant and decorative electroplating,and, in its compounds, for pigments,chemicals, and refractories. The specific gravityis 6.92, melting point 1510°C, and boiling point2200°C. The color is silvery white with a bluishtinge. It is an extremely hard metal; the electrodepositedplates have a hardness of 9 Mohs.It is resistant to oxidation, is inert to HNO3, butdissolves in HCl and slowly in H2SO4. At temperaturesabove 816°C, it is subject to intergranularcorrosion.
Chromium occurs in nature only in combination.Its chief ore is chromite, from which itis obtained by reduction and electrolysis. It ismarketed for use principally in the form of masteralloys with iron or copper.Most pure chromium is used for alloyingpurposes such as the production of Ni–Cr orother nonferrous alloys where the use of thecheaper ferrochrome grades of metal is not possible.In metallurgical operations such as theproduction of low-alloy and stainless steels, thechromium is added in the form of ferrochrome,an electric-arc furnace product that is the formin which most chromium is consumed.
Its bright color and resistance to corrosion makechromium highly desirable for plating plumbingfixtures, automobile radiators and bumpers,and other decorative pieces. Unfortunately,chrome plating is difficult and expensive. Itmust be done by electrolytic reduction ofdichromate in H2SO4 solution. It is customary,therefore, to first plate the object with copper,then with nickel, and finally, with chromium.

Veterinary Drugs and Treatments

Chromium supplementation may be useful in the adjunctive treatment of diabetes mellitus or obesity, particularly in cats; there is controversy whether this treatment is beneficial. It does not appear to be useful in dogs with diabetes mellitus.

Carcinogenicity

Exposure to chromium compounds over a prolonged period has been observed in manyepidemiologicalstudiestoenhancetheriskofcancerof the respiratory organs among the exposed. The relationshipbetweenemploymentinindustriesproducingchromium compounds from chromite ore and enhanced risk of lungcancer iswell established.There isagreement inseveral studies that long-term exposure to some chromium-based pigments enhance the risk of lung cancer. An association has alsobeenobservedbetweenexposuretochromicacidinhard plating and lung cancer, but that association is not strong. Somestudieshaveweaklyindicatedexcessesofcancerofthe GItract,buttheresultsareinconsistentandarenotcon?rmed inwell-designedstudies.Thereisnoindicationthatchromite ore does have an associated enhanced risk of cancer. Although it has not yet been identi?ed which chromium compound (or compounds) is (are) responsible for enhanced risk of cancer in respiratory organs, there is general agreementthatitisthechromium(6+)speciesthatareresponsible for the elevated cancer risks and that the chromium species are not.

Environmental Fate

Chromium is distributed to the air, water, and soil from natural and anthropogenic sources. The environmental fate of chromium is dependent on the oxidation state and solubility of the compound and the environmental conditions affecting reduction or oxidation, such as pH. Oxidizing conditions favor the formation of Cr(VI) compounds, particularly at higher temperatures, while reducing conditions favor the formation of Cr(III) compounds. Chemical manufacturing and natural gas, oil, and gas combustion are the primary sources of chromium in the atmosphere.Most of the chromium in air eventually ends up in water or soil. Electroplating, textile manufacturing, cooling water, and leather tanning are major sources of chromium in wastewater discharges to surface waters.
Chromium(III) is the predominant oxidation state of chromium in many soils. Cr(III) binds to soil and has low mobility. A lower soil pH favors the reduction of Cr(VI) to Cr(III). Runoff from soil and industrial processes may transport chromium to surface water.Cr(VI) compounds may leach into groundwater. The pH of the soil and aquatic environment is an important factor in chromium mobility, bioavailability, and toxicity. The chromate form predominates in most natural surface waters that are basic or neutral. The hydrochromate concentration increases in more acidic conditions.

storage

Color Code—Green (metal, not powder): Generalstorage may be used. Prior to working with chromium youshould be trained on its proper handling and storage. A regulated, marked area should be established where this chemical is handled, used, or stored in compliance with OSHAStandard 1910.1045. Store in tightly closed containers in acool, well-ventilated area. Chromium must be stored toavoid contact with strong oxidizers (such as chlorine, bromine, and fluorine) since violent reactions occur. Sources ofignition, such as smoking and open flames, are prohibitedwhere chromium is used, handled, or stored in a mannerthat could create a potential fire or explosion hazard

Structure and conformation

Two types of chromium crystals, α and β, are obtained depending on the growth method. The β type is semi-stable. It changes to a type above 800℃. The space lattice of β-Cr belongs to the hexagonal system, and its closely-packed hexagonal lattice has lattice constants of a=0.272 nm and c=0.442 nm. The space lattice of α-Cr belongs to the cubic system, and its body-centered cubic lattice has a lattice constant of a=0.28796 nm (18℃).

Toxicity evaluation

Chromium enters the air, water, and soil mostly in the chromium( III) and chromium(VI) forms. In air, chromium compounds are present mostly as fine dust particles, which eventually settle over land and water. Chromium can strongly attach to sediment and soil, and only a small amount is expected to dissolve in water and leach though the soil to groundwater. Fish do not accumulate much chromium in their bodies.
Most chromium exposure in the general population is through ingestion of the chemical in food containing chromium( II), although exposure is also possible as a result of drinking contaminated well water, or living near uncontrolled hazardous waste sites containing chromium or industries that use chromium. Inhalation of chromium dust and skin contact during use in the workplace are the main routes of occupational exposure.

Material Safety Data Sheet(MSDS)

Questions And Answer

Introduction
Chromium occurs in the minerals chromite, FeO•Cr2O3 and crocoite, PbCrO4. The element is never found free in nature. Its abundance in earth's crust is estimated in the range 0.01% and its concentration in sea water is 0.3 μg/L. The element was discovered by Vaquelin in 1797.
The most important application of chromium is in the production of steel. High-carbon and other grades of ferro-chomium alloys are added to steel to improve mechanical properties, increase hardening, and enhance corrosion resistance. Chromium also is added to cobalt and nickel-base alloys for the same purpose.

Refractory bricks composed of oxides of magnesium, chromium, aluminum and iron and trace amounts of silica and calcium oxide are used in roofs of open hearths, sidewalls of electric furnaces and vacuum apparatus and copper converters. Such refractories are made in an arc furnace by fusing mixtures of magnesite and chrome ore.
Chromium coatings are applied on the surface of other metals for decorative purposes, to enhance resistance, and to lower the coefficient of friction. Radioactive chromium–51 is used as a tracer in the diagnosis of blood volume. ;
Chemical Properties
Chromium occurs in oxidation states from Cr^-2 through Cr⁺⁶ but exists mainly in the Cr(III) and Cr(VI) states; Cr(III) is the most stable. Hexavalent chromium compounds have varying physical and chemical properties. Most Cr(VI) compounds are solids; chromyl chloride is a liquid. Their properties include corrosion-resistance, durability, and hardness. Sodium dichromate is the most common chromium chemical from which other Cr(VI) compounds are produced. Examples of other Cr(VI) compounds include sodium chromate, potassium dichromate, potassium chromate, ammonium dichromate, and chromic oxide.
The reduction of Cr(VI) to Cr(III) and the oxidation of Cr(III) to Cr(VI) are important sampling considerations when determining Cr(VI) levels in workplace air (Ashley et al., 2003). Factors that affect the reduction of Cr(VI) or oxidation of Cr(III) include the presence of other compounds in the sample (e.g., iron), the ratio of Cr(VI) to Cr(III) concentrations in the sample, and solution pH. The reduction of Cr(VI) is favored in acidic conditions while Cr(VI) is stabilized in basic conditions. ;
Physical Properties
Hard blue-white metal; body-centered cubic crystal; density 7.19 g/cm3; melts at 1,875°C; vaporizes at 2,199°C; electrical resistivity at 20°C, 12.9 microhm–cm; magnetic susceptibility at 20°C, 3.6x10–6 emu; standard electrode potential 0.71 V (oxidation state 0 to +3). ;
Reactions
Chromium is oxidized readily in air forming a thin, adherent, transparent coating of Cr2O3.
Chromium forms both the chromous (Cr²⁺) and chromic (Cr³⁺) compounds that are highly colored.
Chromium metal reacts readily with dilute acids forming a blue Cr2+ (aq) solution with the evolution of hydrogen:
Cr + 2HCl → CrCl2 + H2
Chromium in metallic form and as Cr2+ ion are reducing agents. The Cr2+ reduces oxygen within minutes, forming violet Cr3+ ion:
4Cr2+(aq) + O2(g) + 4H+ (aq) → 4Cr3+ + 2H2O (l)
The standard redox potential for the overall reaction is 1.64V.
Cr3+ ion forms many stable complex ions. In the aqueous medium, it forms the violet Cr(H2O)63+ ion which is slightly basic. Chromium(III) ion is amphoteric, exhibiting both base and acid behavior.
Chromium reaction in an aqueous solution with a base produces a pale blue-violet precipitate having composition: Cr(H2O)3(OH)3.
Cr(H2O)6³⁺ (aq) + 3OH– (aq) → Cr(H2O)3(OH)3 (s) + H2O
The above precipitate redissolves in excess base:
Cr(H2O)3(OH)3 (s) + H+ (aq) → Cr(H2O)4(OH)2+ (aq) + H2O
Chromium forms chromium(VI) oxide in which the metal is in +6 oxidation state. In acid medium it yields yellow chromate ion, CrO42–, and the redorange dichromate ion, Cr2O₇^2–.
Chromium is oxidized in nitric, phosphoric or perchloric acid forming a thin oxide layer on its surface, thus making the metal even more unreactive to dilute acids.
Elemental chromium reacts with anhydrous halogens, hydrogen fluoride, and hydrogen chloride forming the corresponding chromium halides. At elevated temperatures in the range 600 to 700°C, chromium reacts with hydrogen sulfide or sulfur vapor, forming chromium sulfides.
Chromium metal reacts at 600 to 700°C with sulfur dioxide and caustic alkalis. It combines with phosphorus at 800°C. Reaction with ammonia at 850°C produces chromium nitride, CrN. Reaction with nitric oxide forms chromium nitride and chromium oxide.
5Cr + 3NO → 3CrN + Cr2O3 ;
Production
Chromium metal is produced by thermal reduction of chromium(III) oxide, Cr2O3 by aluminum, silicon or carbon. The starting material in all these thermal reduction processes are Cr2O3 which is obtained from the natural ore chromite after the removal of iron oxide and other impurities. In the aluminum reduction process, the oxide is mixed with Al powder and ignited in a refractory-lined vessel. The heat of reaction is sufficient to sustain the reaction at the required high temperature. Chromium obtained is about 98% pure, containing traces of carbon, sulfur and nitrogen.
Cr2O3 + 2Al→ 2Cr + Al2O3
The carbon reduction process is carried out at 1,300 to 1,400°C at low pressure in a refractory reactor:
Cr2O3 + 3C→ 2Cr + 3CO
The silicon reduction process is not thermally self-sustaining and, therefore, is done in an electric arc furnace:
2Cr2O3 + 3Si → 4Cr + 3 SiO2
Chromium may be produced from high-carbon ferrochrome by electrolytic process. Alternatively, the metal may be obtained by electrolysis of chromic acid, H2CrO4.
High-carbon ferrochromium alloys are made by the reduction of chromite ore with carbon in an arc furnace. On the other hand, low-carbon ferrochromium is obtained by silicon reduction of the ore. The carbon content of ferrochromium can be reduced further by heating high-carbon alloys with ground quartzite or by oxidation in vacuum and removal of carbon monoxide formed. Ferrochromium alloys are used in the manufacture of stainless steel. ;
Toxicity
While chromium metal or trivalent chromium is not very toxic, hexavalent chromium (Cr⁶⁺) is carcinogenic and moderately toxic. Cr⁶⁺ is corrosive to skin and causes denaturation and precipitation of tissue proteins. Inhalation of Cr⁶⁺ dust or mist can cause perforation of the nasal septum, lung irritation, and congestion of the respiratory passsages. Chronic exposure may produce cancer of the respiratory tract. ;

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Isotopes

Origin of Name

Occurrence

Characteristics

Uses

Uses

Uses

Definition

Production Methods

Health Hazard

Industrial uses

Veterinary Drugs and Treatments

Carcinogenicity

Environmental Fate

storage

Structure and conformation

Toxicity evaluation

Material Safety Data Sheet(MSDS)

Questions And Answer

Introduction

Chemical Properties

Physical Properties

Reactions

Production

Toxicity

Well-known Reagent Company Product Information

Supplier

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