2s 2p 3s 3p
Electronic configuration aluminum in excited state :
+13Al * 1s 2
2s 2 2p 6 3s 1 3p 2 1s 2s 2p 3s 3p 
Aluminum exhibits paramagnetic properties. Aluminum in air quickly forms strong oxide films, protecting the surface from further interaction, therefore corrosion resistant.
Physical properties
Aluminum- light metal of silver-white color, easily molded, cast, machined. It has high thermal and electrical conductivity.
Melting point 660 o C, boiling point 1450 o C, aluminum density 2.7 g/cm 3 .
Being in nature
Aluminum- the most common metal in nature, and the 3rd most common among all elements (after oxygen and silicon). Content in earth's crust- about 8%.
In nature, aluminum occurs in the form of compounds:
Bauxites Al 2 O 3 H 2 O(with impurities SiO2, Fe 2 O 3 , CaCO 3)- aluminum oxide hydrate
Corundum Al 2 O 3 . Red corundum is called ruby, blue corundum is called sapphire.
How to get
Aluminum forms a strong chemical bond with oxygen. Therefore, traditional methods for obtaining aluminum by reduction from oxide proceed require large amounts of energy. For industrial aluminum is produced using the Hall-Héroult process. To lower the melting point of alumina dissolved in molten cryolite(at a temperature of 960-970 about C) Na 3 AlF 6 and then subjected to electrolysis with carbon electrodes. When dissolved in a cryolite melt, aluminum oxide decomposes into ions:
Al 2 O 3 → Al 3+ + AlO 3 3-
On the cathode going on reduction of aluminum ions:
K: Al 3+ + 3e → Al 0
On the anode oxidation occurs aluminate ions:
A: 4AlO 3 3- - 12e → 2Al 2 O 3 + 3O 2
The overall equation for the electrolysis of alumina melt:
2Al 2 O 3 → 4Al + 3O 2
laboratory methodthe production of aluminum consists in the reduction of aluminum from anhydrous aluminum chloride with potassium metal:
AlCl 3 + 3K → 4Al + 3KCl
Qualitative reactions
Qualitative reaction to aluminum ions - interaction excessaluminum salts with alkalis . This forms a white amorphous sediment aluminum hydroxide.
For example , aluminum chloride interacts with sodium hydroxide:
With further addition of alkali, amphoteric aluminum hydroxide dissolves to form tetrahydroxoaluminate:
Al(OH) 3 + NaOH = Na
note , if we place an aluminum salt in excess alkali solution, then a white precipitate of aluminum hydroxide is not formed, because in an excess of alkali, aluminum compounds immediately pass into complex:
AlCl 3 + 4NaOH = Na
Aluminum salts can be detected using an aqueous solution of ammonia. In the interaction of soluble aluminum salts with an aqueous solution of ammonia, also in a translucent gelatinous precipitate of aluminum hydroxide precipitates.
AlCl 3 + 3NH 3 H 2 O \u003d Al (OH) 3 ↓ + 3 NH 4 Cl
Al 3+ + 3NH 3 H 2 O\u003d Al (OH) 3 ↓ + 3 NH 4 +
video experience interactions of an aluminum chloride solution with an ammonia solution can be viewed
Chemical properties
1. Aluminum - strong reducing agent . So he reacts with many non-metals .
1.1. Aluminum react with halogens with education halides:
1.2. aluminum reacts with sulfur with education sulfides:
2Al + 3S → Al 2 S 3
1.3. aluminum reactWith phosphorus. In this case, binary compounds are formed - phosphides:
Al + P → AlP
Aluminum does not react with hydrogen .
1.4. With nitrogen aluminum reacts when heated to 1000 ° C with the formation nitride:
2Al +N 2 → 2AlN
1.5. aluminum reacts with carbon with education aluminum carbide:
4Al + 3C → Al 4 C 3
1.6. Aluminum interacts with oxygen with education oxide:
4Al + 3O 2 → 2Al 2 O 3
video experience interactions of aluminum with oxygen in the air(combustion of aluminum in air) can be viewed.
2. Aluminum interacts with complex substances:
2.1. Does the aluminum With water? You can easily find the answer to this question if you dig a little in your memory. Surely at least once in your life you have met with aluminum pans or aluminum cutlery. This is a question I like to ask students in exams. What is most surprising, I received different answers - for someone, aluminum did react with water. And very, very many gave up after the question: “Maybe aluminum reacts with water when heated?” When heated, aluminum reacted with water already in half of the respondents))
However, it is easy to understand that aluminum is still with water under normal conditions (and even when heated) does not interact. And we already mentioned why: because of education oxide film . But if aluminum is cleaned of an oxide film (for example, amalgamate), then it will interact with water very active with education aluminum hydroxide and hydrogen:
2Al 0 + 6H 2 + O → 2Al +3 ( OH) 3 + 3H 2 0
Aluminum amalgam can be obtained by keeping pieces of aluminum in a solution of mercury (II) chloride:
video experience interactions of aluminum amalgam with water can be viewed.
2.2. Aluminum interact with mineral acids (with hydrochloric, phosphoric and dilute sulfuric acid) with an explosion. This produces salt and hydrogen.
For example, aluminum reacts violently with hydrochloric acid :
2.3. Under normal conditions, aluminum does not react With concentrated sulfuric acid due to passivation– formation of a dense oxide film. When heated, the reaction proceeds, forming sulfur(IV) oxide, aluminum sulfate and water:
2Al + 6H 2 SO 4 (conc.) → Al 2 (SO 4) 3 + 3SO 2 + 6H 2 O
2.4. Aluminum does not react with concentrated nitric acid also due to passivation.
FROM dilute nitric acid aluminum reacts to form a molecular nitrogen:
10Al + 36HNO 3 (diff) → 3N 2 + 10Al(NO 3) 3 + 18H 2 O
In the interaction of aluminum in powder form with very dilute nitric acid may form ammonium nitrate:
8Al + 30HNO 3(very dil.) → 8Al(NO 3) 3 + 3NH 4 NO 3 + 9H 2 O
2.5. Aluminum - amphoteric metal, so it interacts with alkalis. When aluminum interacts with solution alkali is formed tetrahydroxoaluminate and hydrogen:
2Al + 2NaOH + 6H 2 O → 2Na + 3H 2
video experience interactions of aluminum with alkali and water can be viewed.
Aluminum reacts with melt alkali with the formation aluminate and hydrogen:
2Al + 6NaOH → 2Na 3 AlO 3 + 3H 2
The same reaction can be written in a different form (in the exam I recommend writing the reaction in this form):
2Al + 6NaOH → NaAlO 2 + 3H 2 + Na 2 O
2.6. aluminum restores less active metals from oxides . The process of recovering metals from oxides is called aluminothermy .
For example, aluminum displaces copper from copper(II) oxide. The reaction is very exothermic:
More example: aluminum restores iron from iron oxide, iron oxide (II, III):
8Al + 3Fe 3 O 4 → 4Al 2 O 3 + 9Fe
Restorative properties aluminum also manifest itself when it interacts with strong oxidizing agents: sodium peroxide, nitrates and nitrites in an alkaline environment permanganates, chromium compounds(VI):
2Al + 3Na 2 O 2 → 2NaAlO 2 + 2Na 2 O
8Al + 3KNO 3 + 5KOH + 18H 2 O → 8K + 3NH 3
10Al + 6KMnO 4 + 24H 2 SO 4 → 5Al 2 (SO 4) 3 + 6MnSO 4 + 3K 2 SO 4 + 24H 2 O
2Al + NaNO 2 + NaOH + 5H 2 O → 2Na + NH 3
Al + 3KMnO 4 + 4KOH → 3K 2 MnO 4 + K
4Al + K 2 Cr 2 O 7 → 2Cr + 2KAlO 2 + Al 2 O 3
Aluminum is a valuable industrial metal that can be recycled. Learn more about the acceptance of aluminum for processing, as well as the current prices for this species metal can .
Aluminium oxide
How to get
Aluminium oxidecan be obtained by various methods:
1. burning aluminum in air:
4Al + 3O 2 → 2Al 2 O 3
2. decomposition aluminum hydroxidewhen heated:
3. Aluminum oxide can be obtained decomposition of aluminum nitrate :
Chemical properties
Aluminum Oxide - Typical amphoteric oxide . Interacts with acidic and basic oxides, acids, alkalis.
1. When aluminum oxide reacts with basic oxides salts are formed aluminates.
For example, aluminum oxide interacts with oxide sodium:
Na 2 O + Al 2 O 3 → 2NaAlO 2
2. Aluminium oxide interacts Wherein in the melt formed salt—aluminates, and in solution - complex salts . At the same time, aluminum oxide exhibits acid properties.
For example, aluminum oxide interacts with sodium hydroxide in the melt to form sodium aluminate and water:
2NaOH + Al 2 O 3 → 2NaAlO 2 + H 2 O
Aluminium oxide dissolves in excess alkalis with education tetrahydroxoaluminate:
Al 2 O 3 + 2NaOH + 3H 2 O → 2Na
3. Aluminum oxide does not interact with water.
4. Aluminum oxide interacts acid oxides (strong acids). At the same time, they form salt aluminum. At the same time, aluminum oxide exhibits basic properties.
For example, aluminum oxide interacts with sulfur oxide (VI) with education aluminum sulfate:
Al 2 O 3 + 3SO 3 → Al 2 (SO 4) 3
5. Aluminum oxide interacts with soluble acids with education medium and acid salts.
For example sulfuric acid:
Al 2 O 3 + 3H 2 SO 4 → Al 2 (SO 4) 3 + 3H 2 O
6. Aluminum oxide exhibits weak oxidizing properties .
For example, aluminum oxide reacts with calcium hydride with education aluminum, hydrogen and calcium oxide:
Al 2 O 3 + 3CaH 2 → 3CaO + 2Al + 3H 2
Electricity restores aluminum from oxide (aluminum production):
2Al 2 O 3 → 4Al + 3O 2
7. Aluminum oxide is a solid, non-volatile. And therefore he displaces more volatile oxides (usually carbon dioxide) from salts during fusion.
For example, from sodium carbonate:
Al 2 O 3 + Na 2 CO 3 → 2NaAlO 2 + CO 2
aluminum hydroxide
How to get
1. Aluminum hydroxide can be obtained by the action of a solution ammonia on the aluminum salts.
For example, aluminum chloride reacts with aqueous ammonia solution with education aluminum hydroxide and ammonium chloride:
AlCl 3 + 3NH 3 + 3H 2 O \u003d Al (OH) 3 + 3NH 4 Cl
2. By passing carbon dioxide , sour gas or hydrogen sulfide through a solution of sodium tetrahydroxoaluminate:
Na + CO 2 \u003d Al (OH) 3 + NaНCO 3
To understand how this reaction proceeds, you can use a simple trick: mentally break complex substance Na into its constituent parts: NaOH and Al(OH) 3 . Next, we determine how carbon dioxide reacts with each of these substances, and record the products of their interaction. Because Al (OH) 3 does not react with CO 2, then we write Al (OH) 3 on the right without change.
3. Aluminum hydroxide can be obtained by the action lack of alkali on the excess aluminum salt.
For example, aluminum chloride reacts with lack of potassium hydroxide with education aluminum hydroxide and potassium chloride:
AlCl 3 + 3KOH (deficient) \u003d Al (OH) 3 ↓ + 3KCl
4. Aluminum hydroxide is also formed by the interaction of soluble aluminum salts with soluble carbonates, sulfites and sulfides . Sulfides, carbonates and sulfites of aluminum in aqueous solution.
For example: aluminum bromide reacts with sodium carbonate. In this case, a precipitate of aluminum hydroxide precipitates, carbon dioxide is released and sodium bromide is formed:
2AlBr 3 + 3Na 2 CO 3 + 3H 2 O \u003d 2Al (OH) 3 ↓ + CO 2 + 6NaBr
aluminum chloride reacts with sodium sulfide with the formation of aluminum hydroxide, hydrogen sulfide and sodium chloride:
2AlCl 3 + 3Na 2 S + 6H 2 O \u003d 2Al (OH) 3 + 3H 2 S + 6NaCl
Chemical properties
1. Aluminum hydroxide reacts with soluble acids. At the same time, they form medium or acid salts, depending on the ratio of reagents and the type of salt.
For example nitric acid with education aluminum nitrate:
Al(OH) 3 + 3HNO 3 → Al(NO 3) 3 + 3H 2 O
Al(OH) 3 + 3HCl → AlCl 3 + 3H 2 O
2Al(OH) 3 + 3H 2 SO 4 → Al 2 (SO 4) 3 + 6H 2 O
Al(OH) 3 + 3HBr → AlBr 3 + 3H 2 O
2. Aluminum hydroxide interacts with acid oxides of strong acids .
For example, aluminum hydroxide interacts with sulfur oxide (VI) with education aluminum sulfate:
2Al(OH) 3 + 3SO 3 → Al 2 (SO 4) 3 + 3H 2 O
3. Aluminum hydroxide interacts with soluble bases (alkalis).Wherein in the melt formed salt—aluminates, and in solution - complex salts . At the same time, aluminum hydroxide exhibits acid properties.
For example, aluminum hydroxide reacts with potassium hydroxide in the melt to form potassium aluminate and water:
2KOH + Al(OH) 3 → 2KAlO 2 + 2H 2 O
aluminum hydroxide dissolves in excess alkalis with education tetrahydroxoaluminate:
Al(OH) 3 + KOH → K
4. G aluminum hydroxide decomposing when heated:
2Al(OH) 3 → Al 2 O 3 + 3H 2 O
video experience interactions of aluminum hydroxide with hydrochloric acid and alkalis (amphoteric properties aluminum hydroxide) can be viewed.
aluminum salts
Aluminum nitrate and sulfate
aluminum nitrate when heated, it decomposes into aluminium oxide, nitric oxide (IV) and oxygen:
4Al(NO 3) 3 → 2Al 2 O 3 + 12NO 2 + 3O 2
aluminum sulfate under strong heating, it decomposes similarly - into aluminium oxide, sulphur dioxide and oxygen:
2Al 2 (SO 4) 3 → 2Al 2 O 3 + 6SO 2 + 3O 2
Complex aluminum salts
To describe the properties of complex aluminum salts - hydroxoaluminates, it is convenient to use the following technique: mentally break tetrahydroxoaluminate into two separate molecules - aluminum hydroxide and alkali metal hydroxide.
For example, sodium tetrahydroxoaluminate is divided into aluminum hydroxide and sodium hydroxide:
Na split into NaOH and Al(OH) 3
The properties of the entire complex can be defined as the properties of these individual compounds.
Thus, aluminum hydroxocomplexes react with acid oxides .
For example, the hydroxocomplex is destroyed under the action of excess carbon dioxide. At the same time, NaOH reacts with CO 2 to form an acid salt (with an excess of CO 2), and amphoteric aluminum hydroxide does not react with carbon dioxide, therefore, it simply precipitates:
Na + CO 2 → Al(OH) 3 ↓ + NaHCO 3
Similarly, potassium tetrahydroxoaluminate reacts with carbon dioxide:
K + CO 2 → Al(OH) 3 + KHCO 3
By the same principle, tetrahydroxoaluminates react with sour gas SO2:
Na + SO 2 → Al(OH) 3 ↓ + NaHSO 3
K + SO 2 → Al(OH) 3 + KHSO 3
But under the action too much strong acid the precipitate does not fall out, because amphoteric aluminum hydroxide reacts with strong acids.
For example, With hydrochloric acid:
Na + 4HCl (excess) → NaCl + AlCl 3 + 4H 2 O
True, under the influence of a small amount ( lack ) strong acid the precipitate will still fall out, there will not be enough acid to dissolve aluminum hydroxide:
Na + HCl (lack) → Al(OH) 3 ↓ + NaCl + H 2 O
Same with disadvantage nitric acid aluminum hydroxide precipitates:
Na + HNO 3 (deficiency) → Al(OH) 3 ↓ + NaNO 3 + H 2 O
The complex is destroyed upon interaction with chlorine water (aqueous chlorine solution) Cl 2:
2Na + Cl 2 → 2Al(OH) 3 ↓ + NaCl + NaClO
At the same time, chlorine disproportionate.
Also, the complex can react with excess aluminum chloride. In this case, a precipitate of aluminum hydroxide precipitates:
AlCl 3 + 3Na → 4Al(OH) 3 ↓ + 3NaCl
If you evaporate water from a solution of a complex salt and heat the resulting substance, then the usual aluminate salt will remain:
Na → NaAlO 2 + 2H 2 O
K → KAlO 2 + 2H 2 O
Hydrolysis of aluminum salts
Soluble salts of aluminum and strong acids are hydrolyzed by cation. Hydrolysis proceeds stepwise and reversible, i.e. a little bit:
Stage I: Al 3+ + H 2 O \u003d AlOH 2+ + H +
Stage II: AlOH 2+ + H 2 O \u003d Al (OH) 2 + + H +
Stage III: Al (OH) 2 + + H 2 O \u003d Al (OH) 3 + H +
However sulfides, sulfites, carbonates aluminum and them sour salt hydrolyzed irreversibly, fully, i.e. do not exist in aqueous solution, but decompose by water:
Al 2 (SO 4) 3 + 6NaHSO 3 → 2Al (OH) 3 + 6SO 2 + 3Na 2 SO 4
2AlBr 3 + 3Na 2 CO 3 + 3H 2 O → 2Al(OH) 3 ↓ + CO 2 + 6NaBr
2Al(NO 3) 3 + 3Na 2 CO 3 + 3H 2 O → 2Al(OH) 3 ↓ + 6NaNO 3 + 3CO 2
2AlCl 3 + 3Na 2 CO 3 + 3H 2 O → 2Al(OH) 3 ↓ + 6NaCl + 3CO 2
Al 2 (SO 4) 3 + 3K 2 CO 3 + 3H 2 O → 2Al(OH) 3 ↓ + 3CO 2 + 3K 2 SO 4
2AlCl 3 + 3Na 2 S + 6H 2 O → 2Al(OH) 3 + 3H 2 S + 6NaCl
Aluminates
Salts in which aluminum is an acid residue (aluminates) are formed from aluminum oxide at fusion with alkalis and basic oxides:
Al 2 O 3 + Na 2 O → 2NaAlO 2
To understand the properties of aluminates, it is also very convenient to break them down into two separate substances.
For example, we mentally divide sodium aluminate into two substances: aluminum oxide and sodium oxide.
NaAlO 2 split into Na 2 O and Al 2 O 3
Then it will become obvious to us that the aluminates react with acids to form aluminum salts :
KAlO 2 + 4HCl → KCl + AlCl 3 + 2H 2 O
NaAlO 2 + 4HCl → AlCl 3 + NaCl + 2H 2 O
NaAlO 2 + 4HNO 3 → Al(NO 3) 3 + NaNO 3 + 2H 2 O
2NaAlO 2 + 4H 2 SO 4 → Al 2 (SO 4) 3 + Na 2 SO 4 + 4H 2 O
Under the action of excess water, aluminates are converted into complex salts:
KAlO 2 + H 2 O = K
NaAlO 2 + 2H 2 O \u003d Na
Binary connections
aluminum sulfide oxidized to sulfate by the action of nitric acid:
Al 2 S 3 + 8HNO 3 → Al 2 (SO 4) 3 + 8NO 2 + 4H 2 O
or to sulfuric acid (under the action of hot concentrated acid):
Al 2 S 3 + 30HNO 3 (conc. horizon) → 2Al(NO 3) 3 + 24NO 2 + 3H 2 SO 4 + 12H 2 O
aluminum sulfide decomposes water:
Al 2 S 3 + 6H 2 O → 2Al(OH) 3 ↓ + 3H 2 S
aluminum carbide also decomposes with water when heated to aluminum hydroxide and methane:
Al 4 C 3 + 12H 2 O → 4Al (OH) 3 + 3CH 4
aluminum nitride decomposes under the action mineral acids on aluminum and ammonium salts:
AlN + 4HCl → AlCl 3 + NH 4 Cl
Aluminum nitride also decomposes under the action of water:
AlN + 3H 2 O → Al(OH) 3 ↓ + NH 3
Aluminum oxide Al 2 O 3 (alumina) is the most important aluminum compound. In its pure form, it is a white, very refractory substance, it has several modifications, of which the most stable are crystalline - Al 2 O 3 and amorphous y - Al 2 O 3. In nature, it occurs in the form of various rocks and minerals.
Of the important properties of Al 2 O 3, the following should be noted:
1) a very hard substance (second only to diamond and some boron compounds);
2) amorphous Al 2 O 3 has a high surface activity and water-absorbing properties - an effective adsorbent;
3) has a high catalytic activity, especially widely used in organic synthesis;
4) is used as a catalyst carrier - nickel, platinum, etc.
According to chemical properties, Al 2 O 3 is a typical amphoteric oxide.
It does not dissolve in water and does not interact with it.
I. Soluble in acids and alkalis:
1) Al 2 O 3 + 6HCl = 2AlCl 3 + ZN 2 O
Al 2 O 3 + 6Н + = 2Al 3+ + ЗН 2 O
2) Al 2 O 3 + 2NaOH + ZN 2 O \u003d 2Na
Al 2 O 3 + 20Н - + ЗН 2 O \u003d 2 [Al (OH) 4] -
II. Alloys with solid alkalis and metal oxides, forming anhydrous metaaluminates:
A 2 O 3 + 2KOH \u003d 2KAlO 2 + H 2 O
A 2 O 3 + MgO \u003d Mg (AlO) 2
Methods for obtaining Al 2 O 3
1. Extraction from natural bauxites.
2. Combustion of Al powder in an oxygen flow.
3. Thermal decomposition of Al(OH) 3 .
4. Thermal decomposition of some salts.
4Al(NO 3) 3 \u003d 2Al 2 O 3 + 12NO 2 + 3O 2
5. Aluminothermy, for example: Fe 2 O 3 + 2Al \u003d Al 2 O 3 + 2Fe
Aluminum hydroxide Al(OH) 3 is a colorless solid, insoluble in water. When heated, it decomposes:
2Al(OH) 3 \u003d Al 2 O 3 + ZN 2 O
Al 2 O 3 obtained in this way is called alumina gel.
According to its chemical properties, it is a typical amphoteric hydroxide, it dissolves in both acids and alkalis:
Al(OH) 3 + 3HCl \u003d AlCl 3 + ZH 2 R
Al(OH) 3 + NaOH = Na sodium tetrahydroxoaluminate
When Al (OH) 3 is fused with solid alkalis, metaaluminates are formed - salts of AlO (OH) metahydroxide, which can be considered as salts of metaaluminum acid HAlO 2:
Al (OH) 3 + NaOH \u003d NaAlO 2 + 2H 2 O
aluminum salts
Due to the amphoteric nature of aluminum hydroxide and the possibility of its existence in ortho- and metaform, there are different types salts. Since Al(OH) 3 exhibits very weak acidic and very weak basic properties, all types of salts in aqueous solutions are highly susceptible to hydrolysis, which ultimately results in the formation of insoluble Al(OH) 3 . The presence of one or another type of aluminum salts in an aqueous solution is determined by the pH value of this solution.
1. Al 3+ salts with anions of strong acids (AlCl 3, Al 2 (SO 4) 3, Al(NO 3) 3, AlBr 3) exist in acidified solutions. In a neutral medium, metaaluminates containing aluminum as part of the AlO 2 anion exist in the solid state. Widespread in nature. When dissolved in water, they transform into hydroxoaluminates.
2. Hydroxoaluminates containing aluminum as an anion - exist in alkaline solutions. In a neutral environment, they are strongly hydrolyzed.
3. Metaaluminates containing aluminum in the composition of the AlO 2 anion. They exist in the solid state. Widespread in nature. When dissolved in water, they transform into hydroxoaluminates.
Interconversions of aluminum salts are described by the scheme:
Methods for precipitation (obtaining) Al (OH) 3 from solutions of its salts
I. Precipitation from solutions containing Al 3+ salts:
Al 3+ + ZONE - \u003d Al (OH) 3 ↓
a) the action of strong alkalis added without excess
AlCl 3 + 3NaOH \u003d Al (OH) 3 ↓ + ZN 2 O
b) the action of aqueous solutions of ammonia (weak base)
AlCl 3 + 3NH 3 + ZN 2 O \u003d Al (OH) 3 ↓ + 3NH 4 Cl
c) the action of salts of very weak acids, the solutions of which, due to hydrolysis, have an alkaline environment (excess OH -)
2AlCl 3 + 3Na 2 CO 3 + 3H 2 O \u003d Al (OH) 3 ↓ + ZSO 2 + 6NaCl
Al 2 (SO 4) 3 + 3K 2 S + 6H 2 O \u003d 2Al (OH) 3 ↓ + 3K 2 SO 4 + 3H 2 S
II. Precipitation from solutions containing hydroxoaluminates:
[Al(OH) 4] - + H + = Al(OH) 3 ↓+ H 2 O
a) the action of strong acids added without excess
Na [Al (OH) 4] + HCl \u003d Al (OH) 3 ↓ + NaCl + H 2 O
2[Al (OH) 4] + H 2 SO 4 \u003d 2Al (OH) 3 ↓ + Na 2 SO 4 + 2H 2 O
b) the action of weak acids, for example, the passage of CO 2
Na [Al (OH) 4] + CO 2 \u003d Al (OH) 3 ↓ + NaHCO 3
III. Precipitation as a result of reversible or irreversible hydrolysis of Al 3+ salts (intensifies when the solution is diluted with water and when heated)
a) reversible hydrolysis
Al 3+ + H 2 O \u003d Al (OH) 2+ + H +
Al 3+ + 2H 2 O \u003d Al (OH) 2 + + 2H +
Al 3+ + 3H 2 O \u003d Al (OH) 3 + + 3H +
b) irreversible hydrolysis
Al 2 S 3 + 6H 2 O \u003d 2Al (OH) 3 ↓ + 3H 2 S
Aluminum- element of the 13th (III) group of the periodic table of chemical elements with atomic number 13. It is designated by the symbol Al. Belongs to the group of light metals. Most common metal and third most common chemical element in the earth's crust (after oxygen and silicon).
Aluminium oxide Al2O3- in nature, it is common as alumina, a white refractory powder, close to diamond in hardness.
Aluminum oxide is a natural compound that can be obtained from bauxites or by thermal decomposition of aluminum hydroxides:
2Al(OH)3 = Al2O3 + 3H2O;
Al2O3 is an amphoteric oxide, chemically inert due to its strong crystal lattice. It does not dissolve in water, does not interact with solutions of acids and alkalis, and can only react with molten alkali.
At about 1000°C, it intensively interacts with alkalis and alkali metal carbonates to form aluminates:
Al2O3 + 2KOH = 2KAlO2 + H2O; Al2O3 + Na2CO3 = 2NaAlO2 + CO2.
Other forms of Al2O3 are more active, can react with solutions of acids and alkalis, α-Al2O3 interacts only with hot concentrated solutions: Al2O3 + 6HCl = 2AlCl3 + 3H2O;
The amphoteric properties of aluminum oxide are manifested when interacting with acidic and basic oxides with the formation of salts:
Al2O3 + 3SO3 = Al2(SO4)3 (basic properties), Al2O3 + Na2O = 2NaAlO2 (acidic properties).
Aluminum hydroxide, Al(OH)3- connection of aluminum oxide with water. White gelatinous substance, poorly soluble in water, has amphoteric properties. Obtained by the interaction of aluminum salts with aqueous solutions of alkali: AlCl3 + 3NaOH \u003d Al (OH) 3 + 3NaCl
Aluminum hydroxide is a typical amphoteric compound, freshly obtained hydroxide dissolves in acids and alkalis:
2Al(OH)3 + 6HCl = 2AlCl3 + 6H2O. Al(OH)3 + NaOH + 2H2O = Na.
When heated, it decomposes, the dehydration process is rather complicated and can be schematically represented as follows:
Al(OH)3 = AlOOH + H2O. 2AlOOH = Al2O3 + H2O.
Aluminates - salts formed by the action of alkali on freshly precipitated aluminum hydroxide: Al (OH) 3 + NaOH \u003d Na (sodium tetrahydroxoaluminate)
Aluminates are also obtained by dissolving metallic aluminum (or Al2O3) in alkalis: 2Al + 2NaOH + 6H2O = 2Na + ZH2
Hydroxoaluminates are formed by the interaction of Al (OH) 3 with an excess of alkali: Al (OH) 3 + NaOH (wt) = Na
aluminum salts. Almost all aluminum salts can be obtained from aluminum hydroxide. Almost all aluminum salts are highly soluble in water; aluminum phosphate is poorly soluble in water.
In an aluminum salt solution, an acid reaction is shown. An example is the reversible effect of aluminum chloride with water:
AlCl3 + 3H2O "Al (OH) 3 + 3HCl
Many aluminum salts are of practical importance. For example, anhydrous aluminum chloride AlCl3 is used in chemical practice as a catalyst in oil refining
Aluminum sulfate Al2(SO4)3 18H2O is used as a coagulant in the purification of tap water, as well as in the production of paper.
Double aluminum salts are widely used - alum KAl (SO4) 2 12H2O, NaAl (SO4) 2 12H2O, NH4Al (SO4) 2 12H2O, etc. - have strong astringent properties and are used in skin tanning, as well as in medical practice as a hemostatic agent.
Application- Due to the complex of properties, it is widely used in thermal equipment. - Aluminum and its alloys retain their strength at ultra-low temperatures. Due to this, it is widely used in cryogenic technology. - Aluminum is an ideal material for the manufacture of mirrors. - In the production of building materials as a gas-forming agent. - Aluminizing gives corrosion and scale resistance to steel and other alloys. development of foam aluminum as a particularly strong and lightweight material.
As a restorer- As a component of thermite, mixtures for aluminothermy - In pyrotechnics. - Aluminum is used to restore rare metals from their oxides or halides. (Aluminothermy)
Aluminothermy.- a method for obtaining metals, non-metals (as well as alloys) by reducing their oxides with metallic aluminum.
One of the most widely used substances in industry is aluminum hydroxide. This article will talk about him.
What is hydroxide?
This is a chemical compound that is formed when an oxide reacts with water. There are three varieties: acidic, basic and amphoteric. The first and second are divided into groups depending on their chemical activity, properties and formula.
What are amphoteric substances?
Oxides and hydroxides can be amphoteric. These are substances that tend to exhibit both acidic and basic properties, depending on the reaction conditions, the reagents used, etc. Amphoteric oxides include two types of iron oxide, oxide of manganese, lead, beryllium, zinc, and aluminum . The latter, by the way, is most often obtained from its hydroxide. Amphoteric hydroxides include beryllium hydroxide, iron hydroxide, and aluminum hydroxide, which we will consider today in our article.
Physical properties of aluminum hydroxide
This chemical compound is a white solid. It doesn't dissolve in water.
Aluminum hydroxide - chemical properties
As mentioned above, this is the brightest representative of the group of amphoteric hydroxides. Depending on the reaction conditions, it can exhibit both basic and acidic properties. This substance is able to dissolve in acids, while forming salt and water.
For example, if you mix it with perchloric acid in equal amounts, then we get aluminum chloride with water in the same proportions. Also, another substance with which aluminum hydroxide reacts is sodium hydroxide. This is a typical basic hydroxide. If we mix in equal quantities the substance in question and a solution of sodium hydroxide, we get a compound called sodium tetrahydroxoaluminate. Its chemical structure contains a sodium atom, an aluminum atom, four atoms of oxygen and four hydrogen atoms. However, when these substances are fused, the reaction proceeds somewhat differently, and this compound is no longer formed. As a result of this process, sodium metaaluminate can be obtained (its formula includes one atom of sodium and aluminum and two atoms of oxygen) with water in equal proportions, provided that you mix the same amount of dry sodium and aluminum hydroxides and act on them with high temperature. If you mix it with sodium hydroxide in other proportions, you can get sodium hexahydroxoaluminate, which contains three sodium atoms, one aluminum atom and six oxygen and hydrogen. In order to form this substance, it is necessary to mix the substance in question and a solution of sodium hydroxide in proportions of 1: 3, respectively. According to the principle described above, compounds called potassium tetrahydroxoaluminate and potassium hexahydroxoaluminate can be obtained. Also, the substance in question is subject to decomposition when exposed to very high temperatures. Due to this kind of chemical reaction, aluminum oxide is formed, which is also amphoteric, and water. If we take 200 g of hydroxide and heat it, we get 50 g of oxide and 150 g of water. In addition to the peculiar chemical properties, this substance also exhibits the properties common to all hydroxides. It interacts with metal salts, which have a lower chemical activity than aluminum. For example, consider the reaction between it and copper chloride, for which you need to take them in a ratio of 2:3. In this case, water-soluble aluminum chloride and a precipitate in the form of cuprum hydroxide will be released in proportions of 2:3. The substance under consideration also reacts with oxides of similar metals, for example, we can take a compound of the same copper. The reaction requires aluminum hydroxide and cuprum oxide in a ratio of 2:3, resulting in aluminum oxide and copper hydroxide. The properties described above also apply to other amphoteric hydroxides, such as iron or beryllium hydroxide.
What is sodium hydroxide?
As seen above, there are many options chemical reactions aluminum hydroxide with sodium hydroxide. What is this substance? It is a typical basic hydroxide, that is, a reactive, water-soluble base. It has all the chemical properties that are characteristic of basic hydroxides.
That is, it can dissolve in acids, for example, by mixing sodium hydroxide with perchloric acid in equal amounts, you can get edible salt (sodium chloride) and water in a 1: 1 ratio. Also, this hydroxide reacts with metal salts, which have a lower chemical activity than sodium, and their oxides. In the first case, a standard exchange reaction occurs. When, for example, silver chloride is added to it, sodium chloride and silver hydroxide are formed, which precipitates (the exchange reaction is feasible only if one of the substances obtained as a result of it is a precipitate, gas or water). When added to sodium hydroxide, for example, zinc oxide, we get the hydroxide of the latter and water. Much more specific, however, are the reactions of this AlOH hydroxide, which have been described above.
Getting AlOH
When we have already considered the main Chemical properties, you can talk about how it is mined. The main way to obtain this substance is to carry out a chemical reaction between an aluminum salt and sodium hydroxide (potassium hydroxide can also be used).
In this kind of reaction, AlOH itself is formed, which precipitates into a white precipitate, as well as a new salt. For example, if you take aluminum chloride and add three times more potassium hydroxide to it, then the resulting substances will be the chemical compound considered in the article and three times more potassium chloride. There is also a method for obtaining AlOH, which involves a chemical reaction between an aluminum salt solution and a base metal carbonate, let's take sodium as an example. To obtain aluminum hydroxide, kitchen salt and carbon dioxide in proportions of 2:6:3, it is necessary to mix aluminum chloride, sodium carbonate (soda) and water in a ratio of 2:3:3.
Where is aluminum hydroxide used?
Aluminum hydroxide finds its application in medicine.
Due to its ability to neutralize acids, preparations containing it are recommended for heartburn. It is also prescribed for ulcers, acute and chronic inflammatory processes of the intestine. In addition, aluminum hydroxide is used in the manufacture of elastomers. It is also widely used in the chemical industry for the synthesis of aluminum oxide, sodium aluminates - these processes were discussed above. In addition, it is often used during water purification from pollution. Also, this substance is widely used in the manufacture of cosmetics.
Where are the substances that can be obtained with it used?
Aluminum oxide, which can be obtained by thermal decomposition of hydroxide, is used in the manufacture of ceramics, and is used as a catalyst for various chemical reactions. Sodium tetrahydroxoaluminate finds its use in textile dyeing technology.
Aluminum oxide - Al2O3. Physical properties: aluminum oxide is a white amorphous powder or very hard white crystals. Molecular weight = 101.96, density - 3.97 g / cm3, melting point - 2053 ° C, boiling point - 3000 ° C.
Chemical properties: aluminum oxide exhibits amphoteric properties - the properties of acidic oxides and basic oxides, and reacts with both acids and bases. Crystalline Al2O3 is chemically passive, amorphous is more active. Interaction with acid solutions gives average aluminum salts, and with base solutions - complex salts - metal hydroxoaluminates:
When aluminum oxide is fused with solid metal alkalis, double salts are formed - metaaluminates(anhydrous aluminates):
Aluminum oxide does not interact with water and does not dissolve in it.
Receipt: aluminum oxide is obtained by the method of aluminum reduction of metals from their oxides: chromium, molybdenum, tungsten, vanadium, etc. - metallothermy, open Beketov:
Application: aluminum oxide is used for the production of aluminum, in the form of a powder - for refractory, chemically resistant and abrasive materials, in the form of crystals - for the manufacture of lasers and synthetic precious stones (rubies, sapphires, etc.), colored with impurities of other metal oxides - Cr2O3 ( red), Ti2O3 and Fe2O3 (blue).
Aluminum hydroxide - A1 (OH) 3. Physical properties: aluminum hydroxide - white amorphous (gel-like) or crystalline. Almost insoluble in water; molecular mass- 78.00, density - 3.97 g / cm3.
Chemical properties: a typical amphoteric hydroxide reacts:
1) with acids, forming medium salts: Al(OH)3 + 3НNO3 = Al(NO3)3 + 3Н2О;
2) with alkali solutions, forming complex salts - hydroxoaluminates: Al(OH)3 + KOH + 2H2O = K.
When Al(OH)3 is fused with dry alkalis, metaaluminates are formed: Al(OH)3 + KOH = KAlO2 + 2H2O.
Receipt:
1) from aluminum salts under the action of an alkali solution: AlCl3 + 3NaOH = Al(OH)3 + 3H2O;
2) decomposition of aluminum nitride with water: AlN + 3H2O = Al(OH)3 + NH3?;
3) passing CO2 through a solution of the hydroxo complex: [Al(OH)4]-+ CO2 = Al(OH)3 + HCO3-;
4) action on Al salts with ammonia hydrate; Al(OH)3 is formed at room temperature.
62. General characteristics of the chromium subgroup
Elements chromium subgroups occupy an intermediate position in the series of transition metals. They have high melting and boiling points, free places in electronic orbitals. Elements chromium and molybdenum have an atypical electronic structure - they have one electron in the outer s-orbital (as in Nb from the VB subgroup). These elements have 6 electrons in the outer d- and s-orbitals, so all orbitals are half-filled, that is, each has one electron. With such an electronic configuration, the element is particularly stable and resistant to oxidation. Tungsten has a stronger metallic bond than molybdenum. The oxidation state of the elements of the chromium subgroup varies greatly. Under proper conditions, all elements exhibit a positive oxidation state from 2 to 6, the maximum oxidation state corresponding to the group number. Not all oxidation states of the elements are stable, chromium has the most stable - +3.
All elements form the MVIO3 oxide; oxides with lower oxidation states are also known. All elements of this subgroup are amphoteric - they form complex compounds and acids.
Chrome, molybdenum and tungsten in demand in metallurgy and electrical engineering. All metals under consideration are covered with a passivating oxide film when stored in air or in an oxidizing acid medium. By removing the film by chemical or mechanical means, it is possible to increase the chemical activity of metals.
Chromium. The element is obtained from chromite ore Fe(CrO2)2 by reducing with coal: Fe(CrO2)2 + 4C = (Fe + 2Cr) + 4CO?.
Pure chromium is obtained by reducing Cr2O3 with aluminum or by electrolysis of a solution containing chromium ions. By recovering chromium by electrolysis, chromium plating can be obtained, which is used as decorative and protective films.
Chromium is used to produce ferrochromium, which is used in the production of steel.
Molybdenum. Obtained from sulfide ore. Its compounds are used in the production of steel. The metal itself is obtained by reducing its oxide. By calcining molybdenum oxide with iron, ferromolybdenum can be obtained. Used for the manufacture of threads and tubes for winding furnaces and electrical contacts. Steel with the addition of molybdenum is used in the automotive industry.
Tungsten. Received from the oxide extracted from the enriched ore. Aluminum or hydrogen is used as a reducing agent. The resulting tungsten in the powder idea is subsequently molded under high pressure and heat treatment (powder metallurgy). In this form, tungsten is used to make filaments, added to steel.