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Aluminum
The second element of group III A is aluminum. Since the atomic radius of aluminum is larger than that of aluminum, the ionization energy is smaller, so the metallic properties of aluminum are stronger than those of boron. is an amphoteric element. Compounds of A1 found in nature.. — bauxite (corundum), Me [2si2o8; Me5 [AL2Si2O 10 ] ; KAI 2 [AISi3 O10 ] (OH)2 – muscovite, ( NA, k)2 [AL2 Si2 O8 ] – nepheline, AI4 [SI4 O10] (OH)8 – kaolinite, Na3 [AIF6]-crolite. It is 5,5% of the total amount of AI in the land postlog. only the compound holiday is found in nature.
Obtainable. Aluminum, mainly bauxite AL2 o3 . Obtained from H2o by electrolysis. Fluorides CaF3, MgF3, AIF3 are added to lower the bauxite liquefaction temperature, the electrolysis process proceeds as follows;
A1 2 o 3 – AI + +AIO-33 (liquefaction)
At cathode: AI+3+3e-AI0
At the anode: 4AIO-3 3 – 12e-2AI2o3+o0
The electrolyzer bridge acts as a cathode. In it, aluminum is released in a liquid state. (T liquid = 66 0 C). At the graphite anode, oxygen is released and oxidizes the graphite to carbon oxides.
Properties Ai-ok, silvery, plastic (soft), good conductor of light electricity, metal that oxidizes in air. In terms of chemical properties, it is directly different from alkaline-earth metals in terms of activity, but it is considered a passive metal due to the formation of an oxide film on its surface. AI – Metallasma enters the raksha:
2AI + 3 SI 2 = 2 ALSI 3
Alkali metals such as aluminum have the property of forming hydrides, which are free of simple and complex hydrides.
2AI+N2 =2AIN
AISI 3 + 4 LIN = LI [ AI N 4] +3 LISI
3 LI [ AIN 4] + AISI 3 = 4 AIN 3 = 3 LISI
AIN 3 + NAH = NA [ AIH 4]
NA [ AIH 4 ] = 2 NAH = NA 3 [ AIH 6]
Aluminum reacts with both acids and bases due to its amphoteric nature.
2AI+6HCI=2AICI3+3H2
2AI+2NAOH+2H2O=2NAAIO3+3H
It also forms a cation complex and an ion complex:
2AI +6H+6H2O=2[AI(OH2)6]3 ++ 3 H2, e0 = — 1,66 B
2AI+ 6 H2O + 6OH-= 2[AI (OH) 6 ] 3 + 3H 2, E= -2 ,35B
2AI + NAOH + 6H2O = 2NA 3 [AI( OH ) 6 ]+3H2
The resulting complex is called salt-sodium hexahydroxyaluminate. Al-metal reacts more easily with alkalis than with acids, because the oxidation potential value of aluminum in an acidic environment is greater than in an alkaline environment. If the upper oxide layer of aluminum is removed with a sharp tool or by forming an amalgam, aluminum dissolves rapidly in water.
2ai+6h2o——-à2ai(oh)3+3h2
When aluminum is exposed to nitric and sulfuric acids, an oxide film forms on its surface, and this oxide acts as a protective layer. Therefore, aluminum metal is more difficult to react with these acids, it does not react in cold solutions.
Aluminum oxide-AI2O3 is a white, water-insoluble substance. It exists in amorphous and crystalline state and dissolves in acids and alkalis. A substance resistant to high temperature. It is called AI203-boxide in nature. It is often obtained by thermal decomposition of AI(0H)3.
2AI (0H)3 —à AI2O3 + 3H2o
AI2O3 obtained by this method is called alumina. Aluminum oxide is soluble in acids and alkalis due to its amphoteric oxidation state:
AI2O3+3H2SO 4 = AI2 ( SO4 )3 + 3H2O (GETS HARD)
AI2 O 3 + 2NAOH= 2NaA IO2 + H2O (EASY TO BE)
NaAAOI2 + 2H2O = NA [ AI( OH) 4 ]
Aluminum hydroxide - AI (OH) 3 is an amphoteric white amorphous substance insoluble in water (PH=7). But if the solution environment changes sharply, it dissolves under the influence of (Ph<7) acids and (Ph>7) alkalis.
AI(OH )3 + 3 H CI= AICI3 + 3H2O
AI(OH)3 +3H+—à AI 3 + + 3H2O = [ AI (H2O) 6] 3+
AI( OH) 3 + NaOH= NA { AI (OH) 4 ]
AI(OH )3 + OH- à [AI(OH)4]-
All water-insoluble hydroxides, such as aluminum hydroxide and aluminum salts, are obtained by the action of alkali:
AICI 3 + 3NAOH = AI (OH) 3 à +3 NACI
The reagents taken for the reaction must be in a strictly equimolar ratio of salt: alkali = 1: 3. This reaction proceeds as follows. When AI - salts are dissolved in water, the AI3 + ion is in the hydrated form [AI(H2O)6 ] 3= and this ion participates in the reaction:
[AI (H2O)6]3++ OH- = [AI(H2O) 5 OH]2++H2O
[AI (H2O)5OH] 2 ++ OH- = [AI(H2O) 4 )OH]2++H2O
[AI (H2O)4(OH)2 ] ++ OH- = [AI(H2O) 3 (OH)3]+H2O
The resulting compound [AI(OH)3-(H2O)3 has a polymer structure and corresponds to the composition AI (OH)3-XH2O. can be explained by the following general (schematic) equation.
N[ AI ( OH2 )6]3= à [ AI ( OH )3]n à n [ AI ( oh )6]3-
[ H3AI3] n
Aluminum crystal hydrates from mostly acidic (pH<7) solutions in this equation;
AI2(SO4)3. 18H3O, AI(NO3)3. 9H2O, AI CI 3 . 6H2O is obtained. Alkaline ( p H>7), various aluminate salts NA [AI(OH)4(H2O) 2], NA3 [AI(OH)6] are obtained from the solutions.
Aluminum salts are hydrolyzed. Hygrolysis reactions proceed in stages. Let's consider this in the example of salt AI2 (SO4)5:
Step 1: H2O
[ AI ( H2O )6]+3 à [ AI ( OH ) ( H2O )5]2+ + ( Ph< 7 )
The resulting complex ion - pentacavo-hygroxaaluminate ion continues to hygrolyze depending on the pH, temperature and salt concentration of the solution.
Phase II:
H2o
[ AI ( OH )( H2O )5]2+ à [ AI ( OH)2 ( H2O )4] + + H= ( Ph<7 )
Phase III:
H2o
[ AI ( OH )2( H2O )4]+ à [ AI ( OH)3 ( H2O )3] + H +
But the last stage occurs at a very low level. usually, hydrolysis stops at the I-II stages, and hydroxo salts of aluminum: [ AI (OH) (H2O) 5] SO4 ; [ AI ( OH)2 ( H2O)4]2 SO4 is formed. If the hydrolysis was complete, AI(OH)3 . x H2O would form a substance that is almost insoluble in water. But AI 3= most salts form clear solutions. The reason for this is that the hydrolysis of aluminum salts does not go to the end.
The dehydrated form of aluminum hydroxide is used as an adsorbent in the "aluminum gel" technique. The reason for the mechanical and chemical stability of the aluminum gel is
AI (OH) 3 . x in H2O (> AI – O à AI <) 'oxol'
|
H
Its bonds are very stable under the influence of temperature (> AI – O à AI <) — it turns into "oxal" bonds.
The aluminum series produces hydroxy, intermediate and double salts. Of these, galangal, sulfate, nitrate, and acetate salts are well soluble in water.
The use of aluminum compounds. The naturally occurring crystalline form of aluminum oxide AI2O3 is called corundum. Fine corundum mixed with sand is called "jilvir". Corundum crystals with a small addition of chromium are called 'ruby'.
Aluminum is widely used in the aviation industry. 2/3 of airplanes are made of aluminum and aluminum alloys. That's why aluminum is also called wing metal. Cables and wires are made of aluminum. The mass of aluminum products, which have a very close electrical conductivity to copper, is twice as light as that of copper products.
Since aluminum does not corrode, it is used for various parts in machine building, containers for transporting nitric acid. The bodies of buses, trolleybuses and wagons are made of aluminum. Various dishes and kettles are made from aluminum in the food industry.
Aluminum and its alloys are also used in the military field in tank construction, artillery, explosives, lighting and incendiary projectiles.
In order to keep iron objects from corrosion, their surface is covered with silvery paint made of aluminum powder.
In metallurgy, many metals are extracted using aluminum. It removes oxygen from the oxides of most metals. The process of recovering metals from their oxides using aluminum is called aluminothermy:
2AI + Cr2O3 à AI2 O3 + 2 C r
Chrome , manganese, vanadium, titanium and other metals from their oxides, aluminothermy method is used to obtain special steels. If aluminum powder FE 3O 4 is mixed with iron soot in equimolar proportions and coated on a metal (iron) wire, an electrode in electric welding is formed. The alloy on the metal surface is called thermite. In electric welding, the following reaction takes place.
8 AI + 3 FE 3 O 4 à 4 AI 2 O 3 + 9 FE.
In this reaction, the heat released in the amount of ^ H= — 3300 kJ causes the iron wire to become liquid and settle on the surface of another iron object.
CHROMIUM AND ITS COMPOUNDS.
Chromium – Cr ( Z = 24 ) is an element of the Vi b group, which also has Mo ( molybdenum ) and W ( 5d 4 6s 2 ). These metals are called corrosion (Cr) and refractory metals (Mo and W) because they are chemically passive and liquefiable at high temperatures. Since the properties of the compounds are similar and widely used, we will focus only on the contributions of chromium and its compounds.
Chromium exhibits various physical and chemical properties. The reason why they are different or similar to other d-metals is explained by the position of chromium element in the periodic system and the electronic structure of its atom.
-3e 0 -3e +6 0 0
Cr 0 ( Ar ) 3 D 5 4s à cR 3 + ( Ar ) 3D 3 4s à Cr ( Ar ) 3D 4S
0
It can be seen that the number of odd electrons in chromium (Cr) metal (atom) is 6, more than in all other elements. therefore chromium alloys have magnetic properties. When moving to Cr3 + compounds, the number of odd electrons decreases, but the magnetic (paramagnetic, ferromagnetic) properties do not disappear, but since the number of main orbitals 3s, 4p, 4d- increases in the Cr3+ ion, its complex formation and the number of compounds of the octahedrite structure increase. . Cr6+ has no odd electrons, therefore it has no magnetic properties, axaryate compounds form a tetrahedral compound due to sp3-hybridization.
Meeting in nature. This metal is mainly found in oxide compounds Fe ( Cro 2 ) 2- chromite, chrome ironstone: PbCro4 – croken holiday.
Obtainable. a) chromium is mainly obtained by aluminothermy method:
Cr 2 O 3 + 2AI =2Cr+ AI2 O 3 ^ G 298 = -510 k J \ MOL
-
b) in most cases, chromium is obtained from an alloy of iron with chromite briquette - chromite, which is heated back with carbon in an electric furnace:
t
Fe ( CrO 2 ) 2 + C == Fe + 2Cr + 4 CO
Common compounds: In the Cr-Mo-W series, the hardness and refractoriness of these metals are second to none. The reason for this is that the stability of the Me-Me covalent bond in the crystal lattice of metals is increased due to d-electrons. At the same time, the chemical activity of these elements decreases. This increases their corrosion resistance.
Properties of chromium group metals.
Properties element |
Cr ( z=24 ) |
Mo ( z=42 ) |
W ( z=74 ) |
Outer electron structure |
3d5 4 s1 |
4d5 5s1 |
5d4 6s2 |
Density, g/ cm3 |
7,2 |
10,2 |
19,3 |
Atomic radius, A |
1,17 |
1,37 |
1,40 |
E+ radius, A |
0,35 |
0,65 |
0,65 |
t liquid 0 C |
1890 |
2620 |
3380 |
t birch 0 C |
3390 |
4800 |
5900 |
Electrical conductivity |
7,1 |
20,2 |
19,3 |
Spread of land postlog ( at% ) |
2 * 10-2 |
3 * 10-4 |
1 * 10-4 |
Characteristic oxidation state |
0;( +2 ); +3; +6 |
0;+2;=4;+6 |
Chromium dissolves in HCI and dilute H 2 SO 4 solutions:
Cr = H 2SO 4 = Cr SO 4 + H2 à
Concentrated HNO 3 and H 2 SO 4 passivate chromium. The reason is the formation of an oxide film Cr2 o 3 on its surface.
Very fine Cr is oxidized under the influence of oxygen and is free of Cr( II ), Cr( III ), and Cr( VI ) compounds in the form of oxides, oxides, acids, hydroxides, salts, and complex compounds.
Oxides. Cr (OH) 2 (basic), Cr (OH) 3 (amphoteric) and H 2 CrO 4 (chromate acid). It can be seen that as the oxidation level of chromium in compounds increases, the basic property weakens and the acidic property increases: Sk (OH)2+ H2SO4= CrSO4 + 2 H2O ( reacts only with acid). Cr 2 o 3 and Cr ( OH ) 3 are amphoteric substances. Cr 2 o 3 dissolves in acids and alkalis:
Cr2 O3 + 6HCI= 2CrCI3 +3H2O
Cr2O3 + 6NAOH (fold) =Na3 CrO3 + 3H2O
The amphotericity of Cr (OH):
[H+] [H+]
[ Cr ( H2O )6]3+ (solution) à Cr ( OH )3( solution) à
[OH]
H3CrO3
[ Cr(OH)6]3-(solution)
Compounds of Cr (II) are reducing agents. Its oxidation potential (E 0 = — 0,4 v ) allows rapid oxidation in aqueous and acidic solutions.
CrCi2 + 2H2O= 2Cr(OH)CI2+H2
4[Cr(H2O)6+2 O2 +4H+= 4[Cr(H2O)6]3+2 H2O
Compounds of Cr (II) have different colors depending on their composition. This also applies to its complex compounds and crystalline solids. The aquacomplex ion [ Cr ( H 2O ) 6 ] 3 = bluish purple, while CrCI3 6H 2 O has a purple color.
Among the common compounds of chromium (III) are sulfated double salts - chromium bitters.
Ulatga K2 SO 4 . Cr 2 ( SO4 ) 3 . 12 H2 O (potassium chromite), (NH4) 2 SO 4 . An example is Cr2 ( SO4) 3 6 H2O (chromic ammonium caustic). They are formed and separated in solution according to the following reaction.
K 2 SO 4 + Cr 2 ( SO 4 ) 3 + 12 H 2 O = K 2 SO 4 . Cr2 ( SO4 ) 3 . 12 H2O
These salts, like other nitrates, chlorides and acetates of chromium, are characterized by good solubility in water. They are hydrolyzed in aqueous solutions and in the melting process. Since the resulting chromium hydroxide ions are a weak base, in most cases these solutions have an acidic environment (pH<7).
Cr ( NO3)3 + 6H2O à [Cr( OH ) ( H2O ) 5 ] (HO3)2 +HNO3
Cr=3 + 6H2O à [Cr (OH) (H2O) 5]2 +H +
The resulting hydroxopentaaquachrome (II) is a complex ion, and its structure is a dimer or polymer holiday. OH – and anions of acid residue act as bridges between Cr 3 + ions. The use of Cr ( III ) compounds as additives in the leather industry is based on the formation of such complex compounds. In them, water molecules are often replaced by the amino acid residue of collagen, which is a part of the skin, and the formed chromium complex plays the role of a binder that sews skin tissues together, dramatically increases its strength, and ensures that the skin turns into leather.
Carbonate and sulphide salts of chromium (III) do not exist in solid form. Because during their extraction, these salts are formed in solution and quickly hydrolyze to form Cr (oh) 3 and CO 2 or H 2 S gases.
2CrCI3 + 3Na2S+6H2O = 2Cr (OH )3 (precipitate) =3H2S (gas) + 6NACI
2Cr+ 3+ 3S2 -+ = 2Cr (OH )3 (precipitate) = 3H2S (gas)
Chromium + 6 oxidation state compounds Cro 3 is a crystalline substance with red color, low solubility in water, good solubility in sulfuric acid, and oxidizing properties. A solution of sulfuric acid is called chromic. H 2 CrO 4 (chrome) or H 2 Cr 2 O 7 (bichromate) acids are holiday in the solution. Therefore, CrO3 is also called chromate anhydride.
H 2 O + CrO 3 = H 2 CrO 4
Chromic acid is a moderately strong acid that is ionized.
H2CrO4 à H+HCrO4 K1= 2*10-1
H2CrO4 à H+HCrO4-2 (chromate anion)
Chromate and dichromate ions NA +, K + , NH 44 + ions form salts that are well soluble in water. Solutions of these salts have strong oxidizing properties:
K2cRo7 + 3 na2 so3 + 4h2so4=cR2(so4)3+ k2so4+4h2o+2na2so4
Oxidizer 2Cr+6 + 2* 3e à 2Cr+3 6 1
Reversible S+4 – 2e à S+6 2 3
Oxidizing property of Cr ( VI ) ion in solutions of common acids
Cr 2 O 7-2 + 14H = = 6 YO à Cr =3 = 7 H2O ( E0 =+1,33v)
It is explained by the reaction. In aqueous solutions, chromates change to dichromates (and vice versa). It depends on the environment (pH) of the solution. if acid solutions (pH<7) are added to the (yellow) solution of chromates, it turns into a reddish-yellow solution (Cr 7 0 7 -2). If H 2 O (a lot) or an alkali solution is added to the bichromate solution, it turns pale yellow, in which Cro 12 4
2 CrO 2 4 + 2H + = Cr2 O 2 7 + H 2O
2 CrO 2 7 + 2H + = 2Cr2 O 4 2 + H 2O
2 CrO 2 forms yellow, yellow-red precipitates with Va (II), Pb (II), Ag (i) ions. It is used as a qualitative reaction to chromate and Va ( II ) ions.
Va2 + = 2 CrO 2 4- = Va Cro 4
If the amount of H=- ions (acid) is increased from chromate solutions, trichromate (K 2 Cr 3 o 10) and tetrachromate (K 2 Cr 4 O13) are formed, in addition to bichromates. The peculiarity of these compounds is that CrO 2 has a 4-group tetrahedral structure, and they form trimer and tetrameric substances by connecting through opposite oxygen atoms.
Chromium and its compounds are used in the following areas. Chrome-preserved alloys are used in holiday special corrosion-resistant steels. That is, chromium acts as an alloying metal. Chrome-plated details are resistant to mechanical wear and work for a long time. Cr ( III ) salts are used as additives in the leather and fur industry, and Cr ( VI ) compounds are used as oxidizing agents. All compounds of chromium are toxic!
Iron and its compounds.
The elements of group VIII V of the periodic table differ greatly from all other groups in terms of structure and arrangement of elements in it. Because the elements included in this group show horizontal similarity instead of vertical similarity, the 9 elements are divided into three families, i.e. triad.
They are as follows: iron triad ( Fe, Co, Ni ), palladium triad ( Ru, Rh, Pd ) and platinum triad ( Os, Ir, Pt ). From these triads, we will get to know the elements of the iron family.
Distribution in nature. Of the elements of the iron family, only iron can be found in nature (celestial bodies) in free form (meteorites). After aluminum, iron is the most common element in nature and exists as oxides and sulfides: Fe3 o 4 e (magnetic emerald), Fe 2 o 3 (red ironstone), 2 Fe 2 O 3 #h2o (brown ironstone). ,Fe CO 3 (ironstone with spar), FeS 2 (iron colchedene or pyrite).
Obtainable. Transferring from iron sulfide oxides to oxides, the oxides are recovered using coke CO gas:
4 FeS2 + 11O 2 = 2Fe2 O3 + 8 SO2
3 Fe 2 O 3 + C = 2Fe3O4 + CO
Fe 3O 4 + 4 CO = 3 Fe + 4 CO 2
Properties element |
Fe (Z=26) |
Co ( Z=22 ) |
Ni ( Z=28 ) |
Electron formula |
(Ar)3d6 4s2 |
(Ar)3d7 4s2 |
(Ar)3d8 4s2 |
Atomic radius, A |
1,26 |
1,25 |
1,24 |
r ion e+2,AE+5, A |
0,800,67 |
0,780,64 |
0,74— |
t 0 boil 0C |
1539 |
1493 |
1453 |
t 0 boil 0C |
2870 |
3100 |
2900 |
Density, g/cm 3 |
7,87 |
8,84 |
8,91 |
E, v(e-2eàE=2) |
-0,44 |
-0,277 |
-0,250 |
Distribution in the Earth's crust, at % |
1,5 |
1 * 10-9 |
3 * 10-9 |