Among the variety of chemical elements and their compounds, it is difficult to single out the most useful substance for mankind. Each is unique in its properties and applications. Technological progress greatly facilitates the research process, but also poses new challenges. Chemical elements, discovered several hundred years ago and studied in all manifestations, receive more technologically advanced uses in the modern world. This trend extends to compounds that exist in nature and created by people.
Oxide
In the earth's crust and in the vastness of the universe, there are many chemical compounds that differ in classes, types, characteristics. One of the most common types of compounds is oxide (oxide, oxide). It includes sand, water, carbon dioxide, i.e. fundamental substances for the existence of mankind and the entire biosphere of the Earth. Oxides are substances that contain oxygen atoms with an oxidation state of -2, while the bond between the elements is binary. Their formation occurs as a result of a chemical reaction, the conditions of which differ depending on the composition of the oxide.
The characteristic features of this substance are three positions: the substance is complex, consists of two atoms, one of them is oxygen. A large number of existing oxides is explained by the fact that many chemical elements form several substances. They are identical in composition, but the atom that reacts with oxygen exhibits several degrees of valency. For example, chromium oxide (2, 3, 4, 6), nitrogen (1, 2, 3, 4, 5), etc. Moreover, their properties depend on the degree of valency of the element entering into the oxidative reaction.
According to the accepted classification, oxides are basic and acidic. An amphoteric species is also distinguished, which exhibits the properties of a basic oxide. Acid oxides are compounds of non-metals or elements with high valence, their hydrates are acids. Basic oxides include all substances that have an oxygen + metal bond, their hydrates are bases.
Chromium
In the 18th century, the chemist I. G. Leman discovered an unknown mineral, which was named red Siberian lead. Vauquelin, a professor at the Paris mineralogical school, carried out a series of chemical reactions with the resulting sample, as a result of which an unknown metal was isolated. The main properties identified by the scientist were its resistance to acidic environments and refractoriness (heat resistance). The name "chromium" (Chromium) arose because of the wide range of colors that characterize the compounds of the element. The metal is quite inert, it is not found in its pure form in natural conditions.
The main minerals containing chromium are: chromite (FeCr 2 O 4), melanochroite, vokelenite, ditzeite, tarapakaite. The chemical element Cr is located in the 6th group of the periodic system of D. I. Mendeleev, has an atomic number of 24. The electronic configuration of the chromium atom allows the element to have a valence of +2, +3, +6, while trivalent metal compounds are the most stable. Reactions are possible in which the oxidation state is +1, +5, +4. Chromium is not chemically active, the metal surface is covered with a film (passivation effect), which prevents reactions with oxygen and water under normal conditions. Chromium oxide, formed on the surface, protects the metal from interaction with acids and halogens in the absence of catalysts. Connections with simple substances (not metals) are possible at a temperature of 300 ° C (chlorine, bromine, sulfur).
When interacting with complex substances, additional conditions are required, for example, the reaction does not occur with an alkali solution, with its melts the process occurs very slowly. Chromium reacts with acids in the presence of high temperature as a catalyst. Chromium oxide can be obtained from various minerals by applying heat. Depending on the future oxidation state of the element, concentrated acids are used. In this case, the chromium valence in the compound varies from +2 to +6 (higher chromium oxide).
Application
Due to the unique anti-corrosion properties and heat resistance, chromium-based alloys are of great practical importance. At the same time, in percentage terms, its share should not exceed half of the total volume. A big disadvantage of chromium is its brittleness, which reduces the possibility of processing alloys. The most common use of metal is the manufacture of coatings (chromium plating). The protective film can be a layer of 0.005 mm, but it will reliably protect the metal product from corrosion and external influences. Chromium compounds are used for the manufacture of heat-resistant structures in the metallurgical industry (melting furnaces). Decorative anti-corrosion coatings (metal-ceramics), special alloyed steel, electrodes for welding machines, alloys based on silicon, aluminum are in demand on world markets. Chromium oxide, due to its low possibility of oxidation and high heat resistance, serves as a catalyst for many chemical reactions occurring at high temperatures (1000 ° C).
Divalent compounds
Chromium oxide (2) CrO (nitrous oxide) is a bright red or black powder. It is insoluble in water, does not oxidize under normal conditions, exhibits pronounced basic properties. The substance is solid, refractory (1550 o C), non-toxic. In the process of heating to 100 about With oxidized to Cr 2 O 3 . It does not dissolve in weak solutions of nitric and sulfuric acids; the reaction occurs with hydrochloric acid.
Getting, applying
This substance is considered the lowest oxide. It has a rather narrow scope. In the chemical industry, chromium oxide 2 is used to purify hydrocarbons from oxygen, which it attracts during oxidation at temperatures above 100 ° C. Divalent chromium oxide can be obtained in three ways:
- Decomposition of carbonyl Cr(CO) 6 in the presence of high temperature as a catalyst.
- Reducing chromium oxide with phosphoric acid 3.
- Chromium amalgam is oxidized with oxygen or nitric acid.
trivalent compounds
For chromium oxides, the +3 oxidation state is the most stable form of the substance. Cr 2 O 3 (chrome green, sesquioxide, escolaide) is chemically inert, insoluble in water, has a high melting point (more than 2000 o C). Chromium oxide 3 - green refractory powder, very hard, has amphoteric properties. The substance is soluble in concentrated acids, the reaction with alkalis occurs as a result of fusion. It can be reduced to pure metal when interacting with a strong reducing agent.
Getting and using
Due to its high hardness (comparable to corundum), the most common use of the substance is in abrasive and polishing materials. Chromium oxide (formula Cr 2 O 3) has a green color, so it is used as a pigment in the manufacture of glasses, paints, and ceramics. For the chemical industry, this substance is used as a catalyst for reactions with organic compounds (ammonia synthesis). Trivalent chromium oxide is used to create artificial gemstones and spinels. Several types of chemical reactions are used to obtain:
- Oxidation of chromium oxide.
- Heating (calcining) ammonium bichromate or chromate.
- Decomposition of trivalent chromium hydroxide or hexavalent oxide.
- Calcination of chromate or mercury dichromate.
Hexavalent compounds
The formula of the highest chromium oxide is CrO 3. The substance is purple or dark red, can exist in the form of crystals, needles, plates. Chemically active, toxic, when interacting with organic compounds there is a danger of spontaneous combustion and explosion. Chromium oxide 6 - chromic anhydride, chromium trioxide - is highly soluble in water, interacts with air under normal conditions (spreads), melting point - 196 ° C. The substance has pronounced acidic characteristics. In a chemical reaction with water, dichromic or chromic acid is formed; without additional catalysts, it interacts with alkalis (yellow chromates). For halogens (iodine, sulfur, phosphorus) is a strong oxidizing agent. As a result of heating above 250 ° C, free oxygen and trivalent chromium oxide are formed.
How is it obtained and where is it used?
Chromium oxide 6 is obtained by treating sodium or potassium chromates (bichromates) with concentrated sulfuric acid or by reacting silver chromate with hydrochloric acid. The high chemical activity of the substance determines the main directions of its application:
- Obtaining pure metal - chromium.
- In the process of chromium plating of surfaces, including by electrolytic method.
- Oxidation of alcohols (organic compounds) in the chemical industry.
- In rocketry, it is used as a propellant igniter.
- In chemical laboratories, it cleans dishes from organic compounds.
- Used in the pyrotechnic industry.
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, H 2 SO 4)
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 an 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, and 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 an ether solution in the presence of H 2 O 2, blue coloring of an 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 and its compounds are actively used in industrial production, in particular, in metallurgy, chemical and refractory industries.
Chromium Cr - a chemical element of the VI group of the periodic system of Mendeleev, atomic number 24, atomic mass 51.996, atomic radius 0.0125, Cr2+ ion radii - 0.0084; Cr3+ - 0.0064; Cr4+ - 6.0056.
Chromium exhibits oxidation states +2, +3, +6, respectively, has valencies II, III, VI.
Chromium is a hard, ductile, rather heavy, malleable steel-gray metal.
Boils at 2469 0 C, melts at 1878 ± 22 0 C. It has all the characteristic properties of metals - it conducts heat well, almost does not resist electric current, and has a luster inherent in most metals. And at the same time, it is resistant to corrosion in air and in water.
Impurities of oxygen, nitrogen and carbon, even in the smallest quantities, dramatically change the physical properties of chromium, for example, making it very brittle. But, unfortunately, it is very difficult to obtain chromium without these impurities.
The structure of the crystal lattice is body-centered cubic. A feature of chromium is a sharp change in its physical properties at a temperature of about 37°C.
6. Types of chromium compounds.
Chromium oxide (II) CrO (basic) is a strong reducing agent, extremely unstable in the presence of moisture and oxygen. Has no practical value.
Chromium oxide (III) Cr2O3 (amphoteric) is stable in air and in solutions.
Cr2O3 + H2SO4 = Cr2(SO4)3 + H2O
Cr2O3 + 2NaOH = Na2CrO4 + H2O
It is formed by heating some chromium (VI) compounds, for example:
4CrO3 2Cr2O3 + 3O2
(NH4)2Cr2O7 Cr2O3 + N2 + 4H2O
4Cr + 3O2 2Cr2O3
Chromium(III) oxide is used to reduce low purity chromium metal with aluminum (aluminothermy) or silicon (silicothermy):
Cr2O3 +2Al = Al2O3 +2Cr
2Cr2O3 + 3Si = 3SiO3 + 4Cr
Chromium oxide (VI) CrO3 (acidic) - dark crimson needle-like crystals.
Obtained by the action of an excess of concentrated H2SO4 on a saturated aqueous solution of potassium dichromate:
K2Cr2O7 + 2H2SO4 = 2CrO3 + 2KHSO4 + H2O
Chromium oxide (VI) is a strong oxidizing agent, one of the most toxic chromium compounds.
When CrO3 is dissolved in water, chromic acid H2CrO4 is formed
CrO3 + H2O = H2CrO4
Acid chromium oxide, reacting with alkalis, forms yellow chromates CrO42
CrO3 + 2KOH = K2CrO4 + H2O
2. Hydroxides
Chromium (III) hydroxide has amphoteric properties, dissolving both in
acids (behaves like a base), and in alkalis (behaves like an acid):
2Cr(OH)3 + 3H2SO4 = Cr2(SO4)3 + 6H2O
Cr(OH)3 + KOH = K
When calcining chromium (III) hydroxide, chromium (III) oxide Cr2O3 is formed.
Insoluble in water.
2Cr(OH)3 = Cr2O3 + 3H2O
3. Acids
Chromium acids corresponding to its +6 oxidation state and differing in the ratio of the number of CrO3 and H2O molecules exist only in the form of solutions. When the acid oxide CrO3 is dissolved, monochromic acid (simply chromic) H2CrO4 is formed.
CrO3 + H2O = H2CrO4
Acidification of a solution or an increase in CrO3 in it leads to acids of the general formula nCrO3 H2O
at n=2, 3, 4, these are, respectively, di, tri, tetrachromic acids.
The strongest of them is dichromic, that is, H2Cr2O7. Chromic acids and their salts are strong oxidizers and poisonous.
There are two types of salts: chromites and chromates.
Chromites with the general formula RCrO2 are salts of chromic acid HCrO2.
Cr(OH)3 + NaOH = NaCrO2 + 2H2O
Chromites vary in color from dark brown to completely black and are usually found in solid masses. Chromite is softer than many other minerals, the melting point of chromite depends on its composition 1545-1730 0 C.
Chromite has a metallic luster and is almost insoluble in acids.
Chromates are salts of chromic acids.
Salts of monochromic acid H2CrO4 are called monochromates (chromates) R2CrO4, salts of dichromic acid H2Cr2O7 dichromates (bichromates) - R2Cr2O7. Monochromats are usually colored yellow. They are stable only in an alkaline environment, and upon acidification they turn into orange-red dichromates:
2Na2CrO4 + H2SO4 = Na2Cr2O7 + Na2SO4 + H2O
] the CrO molecule is assigned numerous R-shaded bands observed in the range of 4800 – 7100 Å in the emission spectrum of an electric arc in air when metallic chromium or Cr 2 Cl 6 salt is placed in it. Vibrational analysis showed that the bands belong to the same system (electronic transition) with a 0-0 band at about 6000 Å, the vibrational constants of the upper and lower electronic states were determined. Bands in the range 7100 – 8400 Å measured in [ 32FER ] are also assigned to the “orange” system. In [55NIN], a partial analysis of the rotational structure of the bands was carried out, on the basis of which the type of electronic transition 5 Π - 5 Π was established. In the handbook [ 84HUG/GER ] the lower state of the system is designated as the ground state of the X 5 Π molecule.
A complete rotational analysis of the five bands of the system (2-0, 1-0, 0-0, 0-1 and 0-2) was performed in [80HOC/MER]. The bands were recorded with high resolution in the emission spectrum of the discharge and in the spectrum of laser excitation of CrO molecules in an inert carrier gas flow. The lower state of the system was confirmed as the ground state of the molecule (the laser excitation spectrum was obtained at a carrier gas temperature slightly below room temperature).
Another weaker system of CrO bands was found in the discharge emission spectrum in the near infrared region [84CHE/ZYR]. The spectrum was obtained using a Fourier spectrometer. Rotational analysis of the 0-0 band, located near 8000 cm -1, showed that the system belongs to the 5 Σ - X 5 Π transition.
The third system of CrO bands, centered at about 11800 cm -1 , was found in the chemiluminescence spectrum during the reaction of chromium atoms with ozone [ 89DEV/GOL ]. The bands of this system are also marked in the atlas [57GAT/JUN]. In [93BAR/HAJ], the 0-0 and 1-1 bands were obtained with high resolution in the laser excitation spectrum. A rotational analysis was carried out, which showed that the system was formed by the 5 Δ - X 5 Π transition.
In the chemiluminescence spectrum [ 89DEV/GOL ] a system of bands was found in the region of 4510 Å (ν 00 = 22163 cm -1), and a vibrational analysis was carried out. The system probably belongs to an electronic transition with charge transfer, since the vibrational interval in the upper state is much smaller than the vibrational intervals in other states of CrO. Pre-electronic transition is designated as C 5 Π - X 5 Π.
The photoelectron spectra of the CrO - anion were obtained in [96WEN/GUN] and [2001GUT/JEN]. The most complete and reliable interpretation of the spectra, based on the MRCI calculation of the anion and molecule, is presented in [2002BAU/GUT]. According to the calculation, the anion has the ground state X 4 Π and the first excited state 6 Σ + . The spectra show one-electron transitions from these states to the ground and 5 excited states of the neutral molecule: X 5 Π ← 6 Σ + (1.12 eV), X 5 Π ← X 4 Π (1.22 eV), 3 Σ – ← X 4 Π (1.82 eV), 5 Σ + ← 6 Σ + (2.13 eV), 3 Π ← X 4 Π (2.28 eV), 5 Δ ← 6 Σ + (2.64 eV), 3 Φ ← X 4 Π (3.03 eV). The energies of the CrO quintet states agree with the data of the optical spectra. The triplet states 3 Σ – (0.6 eV), 3 Π (1.06 eV), and 3 Φ (1.81 eV) were not observed in the optical spectra.
Quantum-mechanical calculations of CrO were performed in [ 82GRO/WAH, 84HUZ/KLO, 85BAU/NEL, 85NEL/BAU, 87AND/GRI, 87DOL/WED, 88JAS/STE, 89STE/NAC, 95BAU/MAI, 96BAK/STI, 2000BRI /ROT, 2000GUT/RAO, 2001GUT/JEN, 2002BAU/GUT, 2003GUT/AND, 2003DAI/DEN, 2006FUR/PER, 2007JEN/ROO, 2007WAG/MIT]. The calculation [85BAU/NEL] showed and confirmed in subsequent calculations that the ground state of the molecule is 5 Π. The energies of excited states are given directly or indirectly (in the form of dissociation energy or electron affinity) in [85BAU/NEL, 85NEL/BAU, 96BAK/STI, 2000BRI/ROT, 2001GUT/JEN, 2002BAU/GUT, 2003DAI/DEN].
The following were included in the calculation of thermodynamic functions: a) the lower component Ω = -1 of the state X 5 Π, as the main state; b) the remaining Ω-components of X 5 Π as separate excited states; c) excited states, the energies of which are determined experimentally or calculated; d) synthetic states that take into account all other states of the molecule with an estimated energy up to 40,000 cm -1 .
The equilibrium constants for the X 5 Π CrO state were obtained in [80HOC/MER]. They are listed in Table Cr.D1 as constants for the lower component X 5 Π –1 , although they refer to the entire state as a whole. Differences in the values of ω e for the components of state X 5 Π are insignificant and are taken into account within an error of ± 1 cm -1 .
The energies of the excited states are given according to the spectroscopic data [ 84CHE/ZYR ] (5 Π 0 , 5 Π 1 , 5 Π 2 , 5 Π 3 , A 5 Σ +), [ 93BAR/HAJ ] ( A΄ 5 Δ), [ 80HOC/MER ] (B 5 Π), [ 89DEV/GOL ] (C 5 Π); interpretation of photoelectron spectra [ 2002BAU/GUT ] (3 Σ - , 3 Π, 3 Φ); according to the calculations [ 2002BAU/GUT ] (5 Σ – , 3 Δ) and [ 2003DAI/DEN ] (3 Σ).
The vibrational and rotational constants of the excited states of CrO were not used in the calculations of thermodynamic functions and are given in Table Cr.D1 for reference. For states A 6 Σ + , A΄ 5 Δ, B 5 Π, C(5 Π) the spectroscopic constants are given according to the data of [84CHE/ZYR, 93BAR/HAJ, 80HOC/MER, 89DEV/GOL], respectively. For the 3 Σ - , 3 Π, 3 Φ states, the values of ω e obtained from the photoelectron spectrum of the anion in [96WEN/GUN] are given. Values ω e for states 5 Σ - , 3 Δ and r e for 3 Σ - , 3 Π, 3 Φ, 5 Σ - , 3 Δ are given according to the results of MRCI calculation [2002BAU/GUT].
The statistical weights of the synthetic states are estimated using the ionic model. The observed and calculated states of CrO are assigned to three ionic configurations: Cr 2+ (3d 4)O 2- , Cr 2+ (3d 3 4s)O 2- and Cr + (3d 5)O - . The energies of other states of these configurations were estimated using the data [71MOO] on the positions of the terms of singly and doubly charged chromium ions. The estimates [2001GUT/JEN] for the energies of the 7 Π, 7 Σ + states of the Cr + (3d 5)O - configuration are also used.
The thermodynamic functions of CrO(g) were calculated using equations (1.3) - (1.6) , (1.9) , (1.10) , (1.93) - (1.95) . Values Q ext and its derivatives were calculated by equations (1.90) - (1.92) taking into account nineteen excited states under the assumption that Q no.vr ( i) = (p i /p X)Q no.vr ( X) . The vibrational-rotational partition function of the X 5 Π -1 state and its derivatives were calculated using equations (1.70) - (1.75) by direct summation over vibrational levels and integration over rotational energy levels using an equation like (1.82) . The calculations took into account all energy levels with values J< J max,v , where J max,v was found from conditions (1.81) . The vibrational-rotational levels of the state X 5 Π -1 were calculated by equations (1.65) , the values of the coefficients Y kl in these equations were calculated using relations (1.66) for the isotopic modification corresponding to the natural mixture of chromium and oxygen isotopes from the molecular constants 52 Cr 16 O given in Table Cr.D1. Coefficient values Y kl , as well as the quantities v max and J lim are given in Table Cr.D2.
At room temperature, the following values are obtained:
C p o (298.15 K) = 32.645 ± 0.26 J × K -1 × mol -1
S o (298.15 K) = 238.481 ± 0.023 J × K -1 × mol -1
H o (298.15 K) - H o (0) = 9.850 ± 0.004 kJ× mol -1
The main contribution to the error of the calculated thermodynamic functions of CrO(g) at temperatures of 298.15 and 1000 K comes from the method of calculation. At 3000 and 6000 K, the error is mainly due to the uncertainty in the energies of the excited electronic states. Errors in the values of Φº( T) at T= 298.15, 1000, 3000 and 6000 K are estimated at 0.02, 0.04, 0.2 and 0.4 J× K -1 × mol -1 , respectively.
Previously, the thermodynamic functions of CrO(g) were calculated for tables by JANAF [85CHA/DAV], Schneider [74SCH] (T = 1000 – 9000 K), Brewer and Rosenblat [69BRE/ROS] (values of Φº( T) for T ≤ 3000 K). Discrepancies between JANAF tables and Table. CrO at low temperatures are due to the fact that the authors of [85CHA/DAV] could not take into account the multiplet splitting of the X 5 Π state; the discrepancy in the values of Φº(298.15) is 4.2 J× K -1 × mol -1 . In the region of 1000 – 3000 K, the discrepancies in the values of Φº( T) do not exceed 1.5 J× K -1 × mol -1 , but by 6000 K they reach 3.1 J× K -1 × mol -1 due to the fact that in [
3.2.1; 3.3.1; 3.7.1; 3.8.1
3.2.1, 3.3.1; 3.4; 3.5
5. The limitation of the validity period was removed according to protocol N 3-93 of the Interstate Council for Standardization, Metrology and Certification (IUS 5-6-93)
6. REPUBLICATION (November 1998) with Amendments No. 1, 2, approved in March 1984, December 1988 (IUS 7-84, 3-89)
This standard applies to chromium (VI) oxide (chromic anhydride), which is dark brown-red acicular or prismatic crystals; soluble in water, hygroscopic.
Formula: CrO.
Molecular weight (according to international atomic masses 1971) - 99.99.
1. TECHNICAL REQUIREMENTS
1. TECHNICAL REQUIREMENTS
1.1. Chromium oxide (VI) must be manufactured in accordance with the requirements of this standard according to the technological regulations approved in the prescribed manner.
(Changed edition, Rev. N 2).
1.2. According to chemical indicators, chromium oxide (VI) must comply with the standards specified in table.1.
Table 1
Name of indicator | ||
Clean for analysis | Pure (h) |
|
1. Mass fraction of chromium oxide (VI) (СrО), %, not less than | ||
2. Mass fraction of substances insoluble in water,%, no more | ||
3. Mass fraction of nitrates (NO),%, no more | Not standardized |
|
4. Mass fraction of sulfates (SO),%, no more | ||
5. Mass fraction of chlorides (Сl), % ,
no more | ||
6. Mass fraction of the sum of aluminum, barium, iron and calcium (Al + Ba + Fe + Ca),% ,
no more | ||
7. Mass fraction of the sum of potassium and sodium (K ± Na),%, no more | ||
2. ACCEPTANCE RULES
2.1. Acceptance rules - according to GOST 3885.
2.2. The determination of the mass fraction of nitrates and the amount of aluminum, barium, iron and calcium is carried out by the manufacturer in every 10th batch.
(Introduced additionally, Rev. N 2).
3. METHODS OF ANALYSIS
3.1a. General instructions for the analysis - according to GOST 27025.
When weighing, laboratory scales are used according to GOST 24104 * 2nd accuracy class with the largest weighing limit of 200 g and 3rd accuracy class with the largest weighing limit of 500 g or 1 kg, or 4th accuracy class with the largest weighing limit of 200 g.
_______________
* Valid GOST 24104-2001. - Note "CODE".
It is allowed to use imported utensils according to the accuracy class and reagents in quality not lower than domestic ones.
3.1. Samples are taken according to GOST 3885.
The mass of the average sample must be at least 150 g.
3.2. Determination of the mass fraction of chromium oxide (VI)
3.1a-3.2. (Changed edition, Rev. N 2).
3.2.1. Reagents, solutions and glassware
Distilled water according to GOST 6709.
Potassium iodide according to GOST 4232, solution with a mass fraction of 30%, freshly prepared.
Hydrochloric acid according to GOST 3118.
Soluble starch according to GOST 10163, solution with a mass fraction of 0.5%.
GOST 27068, concentration solution (NaSO 5HO) = 0.1 mol / dm (0.1 N); prepared according to GOST 25794.2.
Burette with a capacity of 50 ml with a division value of 0.1 cm.
Flask Kn-1-500-29/32 THS according to GOST 25336.
Flask 2-500-2 according to GOST 1770.
Pipettes with a capacity of 2, 10 and 25 ml.
Stopwatch.
Cylinder 1(3)-100 according to GOST 1770.
(Changed edition, Rev. N 1,
3.2.2. Conducting an analysis
About 2.5000 g of the drug is placed in a volumetric flask, dissolved in a small amount of water, the volume of the solution is adjusted to the mark with water and mixed thoroughly.
25 ml of the resulting solution is transferred into a conical flask, 100 ml of water, 5 ml of hydrochloric acid, 10 ml of potassium iodide solution are added, mixed and left in the dark for 10 minutes. Then the stopper is washed off with water, 100 ml of water are added and the released iodine is titrated with a solution of 5-aqueous sodium sulphate, adding 1 ml of starch solution at the end of the titration, until a green color is obtained.
(Changed edition, Rev. N 2).
3.2.3. Results processing
The mass fraction of chromium oxide () as a percentage is calculated by the formula
where is the volume of a solution of 5-aqueous sodium sulphate of concentration exactly (NaSO 5HO) = 0.1 mol / dm (0.1 N) used for titration, cm;
Sample weight, g;
0.003333 - mass of chromium oxide (VI), corresponding to 1 cm3 of a solution of 5-aqueous sodium sulphate concentration exactly (NaSO 5HO) = 0.1 mol / dm (0.1 N), g.
At the same time, a control experiment is carried out with the same amounts of solutions of potassium iodide and hydrochloric acid, and, if necessary, an appropriate correction is made to the result of the determination.
The result of the analysis is taken as the arithmetic mean of the results of two parallel determinations, the absolute discrepancy between which does not exceed the allowable discrepancy of 0.3%.
Permissible absolute total error of the analysis result is ±0.5% at a confidence level =0.95.
(Revised edition, from
m. N 1, 2).
3.3. Determination of the mass fraction of water-insoluble substances
3.3.1. Reagents and glassware
Distilled water according to GOST 6709.
Filtering crucible according to GOST 25336 type TF POR 10 or TF POR 16.
Glass V-1-250 THS according to GOST 25336.
Cylinder 1(3)-250 according to GOST 1770.
3.3.2. Conducting an analysis
30.00 g of the drug is placed in a glass and dissolved in 100 cm3 of water. The beaker is covered with a watch glass and incubated for 1 hour in a water bath. Then the solution is filtered through a filter crucible, previously dried to constant weight and weighed. The result of weighing the crucible in grams is recorded to the fourth decimal place. The residue on the filter is washed with 150 cm3 of hot water and dried in an oven at 105–110°C to constant weight.
The preparation is considered to comply with the requirements of this standard if the mass of the residue after drying does not exceed:
for the drug pure for analysis - 1 mg,
for the drug pure - 3 mg.
Permissible relative total error of the analysis result for the analytical preparation. ± 35%, for the preparation h. ± 20% with a confidence level = 0.95.
3.3.1, 3.3.2. (Changed edition, Rev. N 2).
3.4. Determination of the mass fraction of nitrates
The determination is carried out according to GOST 10671.2. At the same time, 1.50 g of the drug is placed in a flask Kn-2-100-34 (50) TCS (GOST 25336), 100 cm3 of water are added, stirred until dissolved, 1.5 cm3 of concentrated sulfuric acid is added, carefully drop by drop with stirring 2 cm of ethyl alcohol rectified technical top grade (GOST 18300) and heated in a boiling water bath for 15 minutes.
20 cm3 of water are added to the hot solution, and then, with stirring, about 14 cm3 of an ammonia solution with a mass fraction of 10% (GOST 3760) until the chromium is completely precipitated.
The contents of the flask are slowly heated to boiling and boiled for 10 minutes, to avoid ejection, pieces of unglazed porcelain and a glass rod are placed in the flask. Then the liquid is filtered through an ash-free "blue ribbon" filter using a laboratory funnel with a diameter of 75 mm (GOST 25336) (the filter is pre-washed 4-5 times with hot water), the filtrate is collected in a 100 cm3 conical flask with a 60 cm mark. washed three times with hot water, collecting the washings in the same flask. The resulting solution is heated to boiling, boiled for 15 min, cooled, the volume of the solution is adjusted to the mark with water and stirred.
The solution is kept for the determination of chlorides according to clause 3.6.
5 cm3 of the resulting solution (corresponding to 0.125 g of the drug) are placed in a 50 cm3 conical flask, 5 cm3 of water are added, and then the determination is carried out by the method using indigo carmine.
The drug is considered to comply with the requirements of this standard if the color of the analyzed solution observed after 5 minutes is not weaker than the color of the solution prepared at the same time and containing in the same volume:
for the drug pure for analysis 0.005 mg NO,
1 ml of sodium chloride solution, 1 ml of indigo carmine solution and 12 ml of concentrated sulfuric
acids.
3.5. Determination of the mass fraction of sulfates
The determination is carried out according to GOST 10671.5.
At the same time, 0.50 g of the drug is placed in a glass with a capacity of 50 cm3 and dissolved in 5 cm3 of water. The solution is transferred into a separating funnel with a capacity of 50 ml (GOST 25336), 5 ml of concentrated hydrochloric acid, 10 ml of tributyl phosphate are added and shaken.
After separation of the mixture, the aqueous layer is transferred to another identical separating funnel and, if necessary, the treatment of the aqueous layer with 5 ml of tributyl phosphate is repeated. The aqueous layer is separated into a separating funnel and washed with 5 ml of ether for anesthesia. After separation, the aqueous solution is transferred to an evaporating dish (GOST 9147), placed in an electric water bath, and the solution is evaporated to dryness.
The residue is dissolved in 10 cm3 of water, quantitatively transferred into a 50 cm3 conical flask (with a mark of 25 cm3), the volume of the solution is adjusted to the mark with water, mixed, and then the determination is carried out by the visual nephelometric method.
The drug is considered to comply with the requirements of this standard if the observed opalescence of the analyzed solution is not more intense than the opalescence of a solution prepared simultaneously with the analyzed and containing in the same volume:
for the drug pure for analysis - 0.02 mg SO,
for pure preparation - 0.05 mg SO,
1 cm solution of hydrochloric acid with a mass fraction of 10%, 3 cm solution of starch and 3 cm solution of chloride
go barium.
3.6. Determination of the mass fraction of chlorides
The determination is carried out according to GOST 10671.7. In this case, 40 cm3 of the solution obtained according to clause 3.4. (corresponding to 1 g of the drug), placed in a conical flask with a capacity of 100 cm 3 and, if the solution is cloudy, add 0.15 cm optical density of solutions in cuvettes with a thickness of the light-absorbing layer of 100 mm) or by the visual-nephelometric method.
The preparation is considered to comply with the requirements of this standard if the mass of chlorides does not exceed:
for the drug pure for analysis - 0.01 mg,
for the drug pure - 0.02 mg.
At the same time, under the same conditions, a control experiment is carried out to determine the mass fraction of chlorides in the amounts of alcohol and ammonia solution used for analysis, and if they are detected, the analysis results are corrected.
In case of disagreement in the assessment of the mass fraction of chlorides, the determination is carried out by the phototurbidimetric method.
3.4-3.6. (Changed edition, Rev. N 1, 2).
3.7. Determination of the mass fraction of aluminum, barium, iron and calcium
3.7.1. Equipment, reagents and solutions
ISP-30 spectrograph with a three-lens slit illumination system and a three-stage attenuator.
AC arc generator type DG-1 or DG-2.
Rectifier silicon type VAZ-275/100.
Microphotometer type MF-2 or MF-4.
Muffle furnace.
Stopwatch.
Spectroprojector type PS-18.
Organic glass mortars and agate.
Porcelain crucible according to GOST 9147.
Torsion scales VT-500 with a division value of 1 mg or others with a similar accuracy.
Coals graphitized for spectral analysis grade os.ch. 7-3 (carbon electrodes) with a diameter of 6 mm; the upper electrode is sharpened into a cone, the lower one has a cylindrical channel with a diameter of 3 mm and a depth of 4 mm.
Graphite powder, special purity grade, according to GOST 23463.
Spectral photographic plates of the SP-I type with a light sensitivity of 3-5 units. for aluminum, barium and calcium and spectral type SP-III, photosensitivity 5-10 units. for iron.
Ammonium dichromate according to GOST 3763.
Chromium (III) oxide obtained from chromium (VI) oxide according to this standard or ammonium dichromate, with a minimum content of detectable impurities, the determination of which is carried out by the method of additions under the conditions of this method; in the presence of impurities, they are taken into account when constructing a calibration curve.
Aluminum oxide for spectral analysis, chemically pure
Barium oxide grade os.h. 10-1.
Iron (III) oxide, special purity grades 2-4.
Calcium oxide, grade os.h. 6-2.
Ammonium chloride according to GOST 3773.
Distilled water according to GOST 6709.
Hydroquinone (paradioxybenzene) according to GOST 19627.
Potassium bromide according to GOST 4160.
Metol (4-methylaminophenol sulfate) according to GOST 25664.
Sodium sulfite 7-aqueous.
Sodium sulphate (sodium thiosulfate) 5-water according to GOST 27068.
Sodium carbonate according to GOST 83.
Sodium carbonate 10-water according to GOST 84.
Metol hydroquinone developer; prepare as follows: solution A-2 g of metol, 10 g of hydroquinone and 104 g of 7-aqueous sodium sulfite are dissolved in water, the volume of the solution is adjusted to 1 dm with water, stirred and, if the solution is cloudy, it is filtered; solution B-16 g of sodium carbonate (or 40 g of 10-aqueous sodium carbonate) and 2 g of potassium bromide are dissolved in water, the volume of the solution is adjusted to 1 dm with water, mixed and, if the solution is cloudy, it is filtered, then solutions A and B are mixed in equal volumes.
Fast fixer; prepared as follows: 500 g of 5-aqueous sodium sulphate and 100 g of ammonium chloride are dissolved in water, the volume of the solution is adjusted to 2 dm, stirred, and if the solution is cloudy, it is filtered.
Rectified technical ethyl alcohol in accordance with GOST 18300 of the highest grade.
(Changed edition, Rev. N 1, 2).
3.7.2. Preparation for analysis
3.7.2.1. Sample preparation
0.200 g of the drug is placed in a porcelain crucible, dried on an electric stove and calcined in a muffle furnace at 900 °C for 1 hour.
The resulting oxide of chromium (III) is ground in an agate mortar with powdered graphite in a ratio of 1:2.
3.7.2.2. Preparation of samples for building a calibration curve
Samples are prepared on the basis of chromium (III) oxide obtained from chromium (VI) oxide with a minimum content of detectable impurities. To obtain the base, a sample of chromium (VI) oxide is placed in a porcelain crucible, dried on an electric stove, and calcined in a muffle furnace at 900°C for 1 h (it is allowed to prepare samples based on chromium (III) oxide obtained from ammonium dichromate).
The head sample with a mass fraction of each impurity of 0.32% is prepared by grinding 0.0458 g of iron oxide (III), 0.0605 g of aluminum oxide, 0.0448 g of calcium oxide, 0.0357 g of barium oxide and 9.8132 g of chromium oxide (III) in a mortar made of organic glass or agate with 5 cm3 of ethyl alcohol for 1 hour, then dried under an infrared lamp or in an oven, and the mixture is triturated for 30 minutes.
By mixing the appropriate amounts of the head sample or the previous ones with the base, samples with a lower mass fraction of impurities indicated in Table 2 are obtained.
table 2
Sample number | Mass fraction of each impurity (Al, Ba, Fe, Ca) |
Each sample is mixed with powdered graphite in a ratio of 1:2.
3.7.2.1, 3.7.2.2. (Changed edition, Rev. N 2).
3.7.3. Conducting an analysis
The analysis is carried out in a DC arc under the conditions indicated below.
Current strength, A | |
Slot width, mm | |
Diaphragm height on the middle lens of the condenser system, mm | |
exposure, with |
Before taking spectrograms, the electrodes are fired in a DC arc at a current strength of 10–12 A for 30 s.
After firing the electrodes, the analyzed sample or sample is introduced into the channel of the lower electrode (anode) to build a calibration graph. The sample weight is determined by the volume of the channel. The arc is ignited and the spectrogram is taken. The spectra of the analyzed sample and samples are taken on one photographic plate at least three times, each time placing a new pair of electrodes. The slot is opened before the arc is ignited.
The photographic plate with the taken spectra is developed, fixed, washed in running water and dried in air.
3.7.4. Results processing
Photometry of analytical spectral lines of the determined impurities and comparison lines is carried out using a logarithmic scale.
Analytical line | comparison line |
|
Va-233.527 | ||
Cr-391.182 nm |
||
For each analytical pair, the blackening difference () is calculated
where is the blackening of the impurity line;
- blackening of the comparison line or background.
Three values of the blackening difference determine the arithmetic mean value () for each element being determined in the analyzed sample and the sample for constructing a calibration graph.
Based on the values of the samples for constructing calibration graphs, a calibration graph is built for each element to be determined, plotting the concentration logarithms on the abscissa axis, and the arithmetic mean values of the blackening difference on the ordinate axis.
The mass fraction of each impurity is determined from the graph and the result is multiplied by 0.76.
The result of the analysis is taken as the arithmetic mean of the results of three parallel determinations, the relative discrepancy between the most different values of which does not exceed the allowable discrepancy of 50%.
Permissible relative total error of the analysis result is ±20% at a confidence level =0.95.
(Changed edition, Rev. N 2).
3.8. Determination of the mass fraction of the sum of sodium and potassium
3.8.1. Instruments, reagents, solutions and glassware
A flame photometer or a spectrophotometer based on the ISP-51 spectrograph with an FEP-1 attachment, with an appropriate photomultiplier, or a Saturn spectrophotometer. Other instruments providing similar sensitivity and accuracy may be used.
Propane-butane.
Compressed air for power supply of instrumentation.
Burner.
Spray.
Distilled water according to GOST 6709, secondarily distilled in a quartz distiller, or demineralized water.
Solutions containing Na and K; prepared according to GOST 4212, by appropriate dilution and mixing, a solution is obtained with a concentration of Na and K of 0.1 mg / cm - solution A.
Chromium (VI) oxide according to this standard, analytical grade, with the content of Na and K determined by the addition method (solution with a mass fraction of 10%) - solution B.
3.8.2. Preparation for analysis
3.8.2.1. Preparation of analyzed solutions
1.00 g of the drug is dissolved in water, quantitatively transferred into a volumetric flask, the volume of the solution is adjusted to the mark and mixed thoroughly.
3.8.2.2. Preparation of reference solutions
In six volumetric flasks, 10 cm 3 of solution B and the volumes of solution A indicated in Table 3 are introduced.
Table 3
Reference solution number | Volume of solution A, cm | Mass of each element (K, Na) added to 100 ml of reference solution, mg | Mass fraction of each impurity (K, Na) in terms of the preparation, % |
The solutions are mixed, the volume of the solutions is brought to the mark and mixed again.
3.8.2.1, 3.8.2.2. (Changed edition, Rev. N 2).
3.8.3. Conducting an analysis
For analysis take at least two samples of the drug.
The radiation intensity of the resonance lines of sodium 589.0-589.6 nm and potassium 766.5 nm in the gas-air flame spectrum is compared when the analyzed solutions and reference solutions are introduced into it.
After preparing the device for analysis, photometry of the analyzed solutions and reference solutions is carried out in ascending order of the mass fraction of impurities. Then, photometry is carried out in reverse order, starting from the maximum content of impurities, and the arithmetic mean value of the readings for each solution is calculated, taking into account as a correction the reading obtained during photometry of the first reference solution. Spray water after each measurement.
3.8.4. Results processing
Based on the data obtained for reference solutions, a calibration graph is built, plotting the values of the radiation intensity on the ordinate axis, the mass fraction of sodium and potassium impurities in terms of the drug on the abscissa axis.
The mass fraction of sodium and potassium is found according to the schedule.
The result of the analysis is taken as the arithmetic mean of the results of two parallel determinations, the relative discrepancy between which does not exceed the allowable discrepancy of 30%.
Permissible relative total error of the analysis result is ±15% at a confidence level =0.95.
(Changed edition, Rev. N 2).
4. PACKAGING, LABELING, TRANSPORT AND STORAGE
4.1. The drug is packaged and labeled in accordance with GOST 3885.
Type and type of container: 2-4, 2-5, 2-6, 11-6.
Packing group: V, VI, VII.
The product used as a technological raw material is packaged in liners made of a thin polymer film, inserted into metal drums of the BTPB-25, BTPB-50 type (GOST 5044) with a net weight of up to 70 kg.
The container is marked with a danger sign in accordance with GOST 19433 (class 5, subclass 5.1, classification code 5152).
(Changed edition, Rev. N 2).
4.2. The drug is transported by all means of transport in accordance with the rules for the carriage of goods in force on this type of transport.
4.3. The drug is stored in the manufacturer's packaging in covered warehouses.
5. MANUFACTURER WARRANTY
5.1. The manufacturer guarantees the compliance of chromium (VI) oxide with the requirements of this standard, subject to the conditions of transportation and storage.
5.2. Guaranteed shelf life - 3 years from the date of manufacture.
Sec. 5. (Changed edition, Rev. N 2).
6. SAFETY REQUIREMENTS
6.1. Chromium(VI) oxide is poisonous. The maximum permissible concentration in the air of the working area of industrial premises is 0.01 mg / m (1st hazard class). With an increase in concentration, it can cause acute and chronic poisoning with damage to vital organs and systems.
(Changed edition, Rev. N 2).
6.2. When working with the drug, it is necessary to use anti-dust respirators, rubber gloves and goggles, as well as observe the rules of personal hygiene; do not allow the drug to enter the body.
6.3. Maximum sealing of process equipment should be ensured.
6.4. Premises in which work with the drug is carried out should be equipped with general supply and exhaust ventilation, and places of the greatest dust - with shelters with local exhaust ventilation. The analysis of the drug should be carried out in a laboratory fume hood.
(Changed edition, Rev. N 2).
6.5. When analyzing the drug using combustible gases, fire safety rules should be observed.
The text of the document is verified by:
official publication
M.: IPK Standards Publishing House, 1999
