EntranceThe most important compounds of aluminum. Aluminum hydroxide Aluminum hydroxide physical and chemical properties
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. It occurs in nature in the form of various rocks and minerals.
From important properties 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 high surface activity and water-absorbing properties - an effective adsorbent;
3) has high catalytic activity, especially widely used in organic synthesis;
4) used as a carrier for catalysts - nickel, platinum, etc.
In terms of chemical properties, Al 2 O 3 is a typical amphoteric oxide.
It does not dissolve in water and does not interact with it.
I. Dissolves 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 + ZH 2 O = 2Na
Al 2 O 3 + 20H - + ZH 2 O = 2[Al(OH) 4 ] -
II. Fuses with solid alkalis and metal oxides, forming anhydrous metaaluminates:
A 2 O 3 + 2KOH = 2KAlO 2 + H 2 O
A 2 O 3 + MgO = Mg(AlO) 2
Methods for producing Al 2 O 3
1. Extraction from natural bauxite.
2. Combustion of Al powder in a flow of oxygen.
3. Thermal decomposition of Al(OH) 3.
4. Thermal decomposition of some salts.
4Al(NO 3) 3 = 2Al 2 O 3 + 12NO 2 + 3O 2
5. Aluminothermy, for example: Fe 2 O 3 + 2Al = Al 2 O 3 + 2Fe
Aluminum hydroxide Al(OH) 3 is a solid, colorless substance, insoluble in water. When heated, it decomposes:
2Al(OH) 3 = Al 2 O 3 + ZN 2 O
The Al 2 O 3 obtained in this way is called aluminogel.
According to its chemical properties, it is a typical amphoteric hydroxide, soluble in both acids and alkalis:
Al(OH) 3 + 3HCl = AlCl 3 + ZN 2 P
Al(OH) 3 + NaOH = Na sodium tetrahydroxoalumicate
When Al(OH) 3 is fused with solid alkalis, metaaluminates are formed - salts of metahydroxide AlO(OH), which can be considered as salts of metaaluminum acid HAlO 2:
Al(OH) 3 + NaOH = NaAlO 2 + 2H 2 O
Aluminum salts
Due to the amphoteric nature of aluminum hydroxide and the possibility of its existence in ortho- and metaforms, there are different types of 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. Presence in aqueous solution of one type or another of aluminum salts is determined by the pH value of a given solution.
1. Al 3+ salts with strong acid anions (AlCl 3, Al 2 (SO 4) 3, Al(NO 3) 3, AlBr 3) exist in acidified solutions. In a neutral environment, metaaluminates containing aluminum as part of the AlO 2 anion exist in the solid state. Distributed in nature. When dissolved in water they turn into hydroxoaluminates.
2. Hydroxoaluminates containing aluminum as part of the - anion exist in alkaline solutions. In a neutral environment they are highly hydrolyzed.
3. Metaaluminates containing aluminum as part of the AlO 2 anion. They exist in a solid state. Distributed in nature. When dissolved in water they turn into hydroxoaluminates.
Interconversions of aluminum salts are described by the following scheme:
Methods for precipitation (obtaining) Al(OH) 3 from solutions of its salts
I. Precipitation from solutions containing Al 3+ salts:
Al 3+ + ZON - = Al(OH) 3 ↓
a) the effect of strong alkalis added without excess
AlCl 3 + 3NaOH = Al(OH) 3 ↓ + ZH 2 O
b) the effect of aqueous solutions of ammonia (weak base)
AlCl 3 + 3NH 3 + ZH 2 O = Al(OH) 3 ↓ + 3NH 4 Cl
c) the effect of salts of very weak acids, solutions of which, due to hydrolysis, have an alkaline environment (excess OH -)
2AlCl 3 + 3Na 2 CO 3 + 3H 2 O = Al(OH) 3 ↓ + 3CO 2 + 6NaCl
Al 2 (SO 4) 3 + 3K 2 S + 6H 2 O = 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 effect of strong acids added without excess
Na[Al(OH) 4 ] + HCl = Al(OH) 3 ↓ + NaCl + H 2 O
2[Al(OH) 4 ] + H 2 SO 4 = 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 = 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 = Al(OH) 2+ + H +
Al 3+ + 2H 2 O = Al(OH) 2 + + 2H +
Al 3+ + 3H 2 O = Al(OH) 3 + + 3H +
b) irreversible hydrolysis
Al 2 S 3 + 6H 2 O = 2Al(OH) 3 ↓ + 3H 2 S
One of the most widely used substances in industry is aluminum hydroxide. This article will talk about it.
What is hydroxide?
This is a chemical compound that is formed when an oxide reacts with water. There are three types of them: 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, 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 does not dissolve in water.
Aluminum hydroxide - chemical properties
As mentioned above, this is the most striking representative of the group of amphoteric hydroxides. Depending on the reaction conditions, it can exhibit both basic and acid properties. This substance can dissolve in acids, resulting in the formation of salt and water.
For example, if you mix it with perchloric acid in equal quantities, you will get aluminum chloride with water also in equal proportions. Also, another substance that aluminum hydroxide reacts with is sodium hydroxide. This is a typical basic hydroxide. If you mix the substance in question and a solution of sodium hydroxide in equal quantities, you get a compound called sodium tetrahydroxyaluminate. In his chemical structure contains a sodium atom, an aluminum atom, four atoms of oxygen and hydrogen. However, when these substances are fused, the reaction proceeds somewhat differently, and it is no longer this compound that is formed. As a result of this process, it is possible to obtain sodium metaaluminate (its formula includes one atom of sodium and aluminum and two atoms of oxygen) with water in equal proportions, provided that the same amount of dry sodium and aluminum hydroxides is mixed and exposed to high temperature. If you mix it with sodium hydroxide in other proportions, you can get sodium hexahydroxyaluminate, which contains three sodium atoms, one aluminum atom and six each of oxygen and hydrogen. In order for this substance to be formed, you need to mix the substance in question and a solution of sodium hydroxide in proportions of 1:3, respectively. Using the principle described above, compounds called potassium tetrahydroxoaluminate and potassium hexahydroxoaluminate can be obtained. Also, the substance in question is susceptible to decomposition when exposed to very high temperatures. As a result of this kind of chemical reaction, aluminum oxide, which is also amphoteric, and water are formed. If you take 200 g of hydroxide and heat it, you get 50 g of oxide and 150 g of water. In addition to the peculiar chemical properties, this substance also exhibits properties common to all hydroxides. It interacts with metal salts, which have lower chemical activity than aluminum. For example, we can 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 in question also reacts with oxides of similar metals; for example, we can take a compound of the same copper. To carry out the reaction, you will need aluminum hydroxide and cuprum oxide in a ratio of 2:3, resulting in aluminum oxide and copper hydroxide. Other amphoteric hydroxides, such as iron or beryllium hydroxide, also have the properties described above.
What is sodium hydroxide?
As you can see above, there are many options chemical reactions aluminum hydroxide with sodium hydroxide. What kind of substance is this? 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, when mixing sodium hydroxide with perchloric acid in equal quantities, you can get table salt (sodium chloride) and water in a 1:1 ratio. This hydroxide also reacts with metal salts, which have 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 precipitate (the exchange reaction is feasible only if one of the substances resulting from it is a precipitate, gas or water). When adding, for example, zinc oxide to sodium hydroxide, we obtain the latter's hydroxide and water. However, much more specific are the reactions of this hydroxide AlOH, which were described above.
Preparation of AlOH
When we have already considered its main Chemical properties, we 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).
With 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, the resulting substances will be the chemical compound discussed in the article and three times more potassium chloride. There is also a method for producing AlOH, which involves carrying out a chemical reaction between a solution of an aluminum salt and a carbonate of the base metal; let’s take sodium as an example. To obtain aluminum hydroxide, kitchen salt and carbon dioxide in a ratio of 2:6:3, you need 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 use 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 intestines. 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 and sodium aluminates - these processes were discussed above. In addition, it is often used when purifying water from contaminants. This substance is also widely used in the manufacture of cosmetics.
Where are the substances that can be obtained with its help used?
Aluminum oxide, which can be obtained due to the thermal decomposition of hydroxide, is used in the manufacture of ceramics and is used as a catalyst for carrying out various chemical reactions. Sodium tetrahydroxyaluminate finds its use in fabric dyeing technology.
The appearance of the substance aluminum hydroxide is as follows. As a rule, this substance is white, gelatinous in appearance, although there are variants of its presence in a crystalline or amorphous state. For example, when dried, it crystallizes into white crystals that do not dissolve in either acids or alkalis.
Aluminum hydroxide can also be presented as a fine-crystalline white powder. The presence of pink and gray shades is acceptable.
Chemical formula compounds - Al(OH)3. The compound and water form a hydroxide which is also determined largely by the elements included in its composition. This compound is obtained by reacting an aluminum salt and a dilute alkali, but an excess of them should be avoided. The aluminum hydroxide precipitate obtained during this reaction can then react with acids.
Aluminum hydroxide reacts with an aqueous solution of rubidium hydroxide, an alloy of this substance, cesium hydroxide, and cesium carbonate. In all cases, water is released.
Aluminum hydroxide has a value of 78.00 and is practically insoluble in water. The density of the substance is 3.97 grams/cm3. Being an amphoteric substance, aluminum hydroxide reacts with acids, and as a result of the reactions, medium salts are obtained and water is released. When reacting with alkalis, complex salts appear - hydroxoaluminates, for example, K. Metaaluminates are formed if aluminum hydroxide is fused with anhydrous alkalis.
Like all amphoteric substances, aluminum hydroxide simultaneously exhibits acidic and basic properties when interacting with and also with alkalis. In these reactions, when the hydroxide is dissolved in acids, the ions of the hydroxide itself are eliminated, and when interacting with an alkali, a hydrogen ion is eliminated. To see this, you can, for example, carry out a reaction that involves aluminum hydroxide. To carry it out, you need to pour some aluminum sawdust into a test tube and fill it with a small amount of sodium hydroxide, no more than 3 milliliters. The test tube should be tightly capped and slowly heated. After this, having secured the test tube on a stand, you need to collect the released hydrogen into another test tube, having first placed it on a capillary device. After about a minute, the test tube should be removed from the capillary and brought to the flame. If pure hydrogen is collected in a test tube, combustion will occur quietly, but if air gets into it, a bang will occur.
Aluminum hydroxide is obtained in laboratories in several ways:
By reaction between aluminum salts and alkaline solutions;
The method of decomposition of aluminum nitride under the influence of water;
By passing carbon through a special hydrocomplex containing Al(OH)4;
The effect of ammonia hydrate on aluminum salts.
Industrial production associated with the processing of bauxite. Technologies of exposure of aluminate solutions to carbonates are also used.
Aluminum hydroxide is used in the production of mineral fertilizers, cryolite, and various medical and pharmacological preparations. IN chemical production the substance is used to produce aluminum fluoride and sulphide. An indispensable compound in the production of paper, plastics, paints and much more.
Medical use is due to the positive effect of drugs containing this element in the treatment of gastric disorders, increased acidity of the body, and peptic ulcers.
When handling the substance, you should be careful not to inhale its vapors, as they cause severe lung damage. Being a weak laxative, it is dangerous in large doses. When corroded, it causes aluminosis.
The substance itself is quite safe, as it does not react with oxidizing agents.
2s 2p 3s 3p
Electronic configuration aluminum V excited state :
+13Al * 1s 2
2s 2 2p 6 3s 1 3p 2 1s 2s 2p 3s 3p 
Aluminum exhibits paramagnetic properties. Aluminum quickly forms in air durable oxide films, protecting the surface from further interaction, therefore corrosion resistant.
Physical properties
Aluminum– a light metal of silver-white color, easy to form, cast, and machine. 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 abundant among all elements (after oxygen and silicon). Contents in earth's crust- about 8%.
In nature, aluminum occurs in the form of compounds:
Bauxite 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.
Methods of obtaining
Aluminum forms a strong chemical bond with oxygen. Therefore, traditional methods for producing aluminum by reduction from oxide require large amounts of energy. For industrial Aluminum is produced using the Hall-Heroult process. To lower the melting point of aluminum oxide dissolved in molten cryolite(at a temperature of 960-970 o C) Na 3 AlF 6 and then subjected to electrolysis with carbon electrodes. When dissolved in cryolite melt, aluminum oxide breaks down into ions:
Al 2 O 3 → Al 3+ + AlO 3 3-
On cathode is happening reduction of aluminum ions:
K: Al 3+ +3e → Al 0
On anode oxidation occurs aluminate ions:
A: 4AlO 3 3- - 12e → 2Al 2 O 3 + 3O 2
The overall equation for the electrolysis of molten aluminum oxide is:
2Al 2 O 3 → 4Al + 3O 2
Laboratory methodAluminum production involves 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 produces 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 tetrahydroxyaluminate:
Al(OH) 3 + NaOH = Na
note , if we put aluminum salt in excess alkali solution, then a white precipitate of aluminum hydroxide is not formed, because in excess of alkali, aluminum compounds immediately transform into complex:
AlCl 3 + 4NaOH = Na
Aluminum salts can be detected using an aqueous ammonia solution. When soluble aluminum salts interact with an aqueous solution of ammonia, also in A translucent gelatinous precipitate of aluminum hydroxide precipitates.
AlCl 3 + 3NH 3 H 2 O = Al(OH) 3 ↓ + 3 NH 4 Cl
Al 3+ + 3NH 3 H 2 O= Al(OH) 3 ↓ + 3 NH 4 +
Video experience the interaction of aluminum chloride solution with ammonia solution can be seen
Chemical properties
1. Aluminum – strong reducing agent . So he reacts with many non-metals .
1.1. Aluminum reacts 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 o C to form 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 interaction of aluminum with oxygen in the air(combustion of aluminum in air) can be viewed.
2. Aluminum interacts with complex substances:
2.1. Is it responsive? aluminum With water? You can easily find the answer to this question if you delve a little into your memory. Surely at least once in your life you have come across aluminum pans or aluminum cutlery. This is the question I liked to ask students during exams. What is most surprising is that I received different answers - for some, aluminum did react with water. And very, very many people gave up after the question: “Maybe aluminum reacts with water when heated?” When heated, aluminum reacted with water in half of the respondents))
However, it is easy to understand that aluminum is still with water under normal conditions (and even when heated) doesn't interact. And we have already mentioned why: because of education oxide film . But if aluminum is cleaned from the 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 The interaction of aluminum amalgam with water can be viewed.
2.2. Aluminum interacts 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 because of 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.
WITH dilute nitric acid aluminum reacts to form a molecular nitrogen:
10Al + 36HNO 3 (diluted) → 3N 2 + 10Al(NO 3) 3 + 18H 2 O
When aluminum in powder form interacts with very dilute nitric acid may form ammonium nitrate:
8Al + 30HNO 3(highly diluted) → 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 tetrahydroxyaluminate And hydrogen:
2Al + 2NaOH + 6H 2 O → 2Na + 3H 2
Video experience The interaction 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 another form (in the Unified State Examination 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 reducing metals from oxides is called aluminothermy .
For example, aluminum is displacing copper from copper(II) oxide. The reaction is very exothermic:
More example: aluminum restores iron from iron scale, iron (II, III) oxide:
8Al + 3Fe 3 O 4 → 4Al 2 O 3 + 9Fe
Restorative properties aluminum also manifest themselves 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. You can find out more about accepting aluminum for processing, as well as current prices for this type of metal. .
Aluminium oxide
Methods of obtaining
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 interacts 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 are formed salt—aluminates, and in solution - complex salts . In this case, aluminum oxide exhibits acid properties.
For example, aluminum oxide interacts with sodium hydroxide in the melt with the formation sodium aluminate And water:
2NaOH + Al 2 O 3 → 2NaAlO 2 + H 2 O
Aluminium oxide dissolves in excess alkalis with education tetrahydroxyaluminate:
Al 2 O 3 + 2NaOH + 3H 2 O → 2Na
3. Aluminum oxide does not react with water.
4. Aluminum oxide reacts acid oxides (strong acids). In this case, salt aluminum In this case, aluminum oxide exhibits basic properties.
For example, aluminum oxide interacts with sulfur(VI) oxide with education aluminum sulfate:
Al 2 O 3 + 3SO 3 → Al 2 (SO 4) 3
5. Aluminum oxide reacts 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 solid and 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
Methods of obtaining
1. Aluminum hydroxide can be obtained by the action of a solution ammonia on 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 = Al(OH) 3 + 3NH 4 Cl
2. By passing carbon dioxide, sulfur dioxide or hydrogen sulfide through sodium tetrahydroxyaluminate solution:
Na + CO 2 = Al(OH) 3 + NaHCO 3
To understand how this reaction proceeds, you can use a simple technique: mentally break down compound Na into its components: 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 prepared by lack of alkali on excess aluminum salt.
For example, aluminum chloride reacts with potassium hydroxide deficiency with education aluminum hydroxide And potassium chloride:
AlCl 3 + 3KOH (insufficient) = Al(OH) 3 ↓+ 3KCl
4. Also, aluminum hydroxide is formed by the interaction of soluble aluminum salts with soluble carbonates, sulfites and sulfides . Aluminum sulfides, carbonates and sulfites 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 = 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 = 2Al(OH) 3 + 3H 2 S + 6NaCl
Chemical properties
1. Aluminum hydroxide reacts with soluble acids. In this case, 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 reacts with acid oxides of strong acids .
For example, aluminum hydroxide reacts with sulfur(VI) oxide with education aluminum sulfate:
2Al(OH) 3 + 3SO 3 → Al 2 (SO 4) 3 + 3H 2 O
3. Aluminum hydroxide reacts with soluble bases (alkalis).Wherein in the melt are formed salt—aluminates, and in solution - complex salts . In this case, aluminum hydroxide exhibits acid properties.
For example, aluminum hydroxide reacts with potassium hydroxide in the melt with the formation potassium aluminate And water:
2KOH + Al(OH) 3 → 2KAlO 2 + 2H 2 O
Aluminum hydroxide dissolves in excess alkalis with education tetrahydroxyaluminate:
Al(OH) 3 + KOH → K
4. G aluminum hydroxide decomposes when heated:
2Al(OH) 3 → Al 2 O 3 + 3H 2 O
Video experience interaction of aluminum hydroxide with hydrochloric acid And alkalis(amphoteric properties of 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 when heated strongly, it decomposes in a similar way - 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 tetrahydroxyaluminate is broken down into aluminum hydroxide and sodium hydroxide:
Na break it down into NaOH and Al(OH) 3
The properties of the entire complex can be determined as the properties of these individual compounds.
Thus, aluminum hydroxo complexes react with acid oxides .
For example, the hydroxo complex is destroyed under the influence of excess carbon dioxide. In this case, 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, simply precipitates:
Na + CO 2 → Al(OH) 3 ↓ + NaHCO 3
Similarly, potassium tetrahydroxyaluminate reacts with carbon dioxide:
K + CO 2 → Al(OH) 3 + KHCO 3
By the same principle, tetrahydroxoaluminates react with sulfur dioxide SO 2:
Na + SO 2 → Al(OH) 3 ↓ + NaHSO 3
K + SO 2 → Al(OH) 3 + KHSO 3
But under the influence excess strong acid no precipitate forms, 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 A precipitate will still form; there will not be enough acid to dissolve aluminum hydroxide:
Na + HCl (deficiency) → Al(OH) 3 ↓ + NaCl + H 2 O
Same with the disadvantage nitric acid aluminum hydroxide precipitates:
Na + HNO 3 (deficiency) → Al(OH) 3 ↓ + NaNO 3 + H 2 O
The complex is destroyed when interacting with chlorine water (aqueous chlorine solution) Cl 2:
2Na + Cl 2 → 2Al(OH) 3 ↓ + NaCl + NaClO
At the same time, chlorine disproportions.
The complex may also 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, you will be left with the usual aluminate salt:
Na → NaAlO 2 + 2H 2 O
K → KAlO 2 + 2H 2 O
Hydrolysis of aluminum salts
Soluble aluminum salts and strong acids are hydrolyzed by cation. Hydrolysis proceeds stepwise and reversible, i.e. a little:
Stage I: Al 3+ + H 2 O = AlOH 2+ + H +
Stage II: AlOH 2+ + H 2 O = Al(OH) 2 + + H +
Stage III: Al(OH) 2 + + H 2 O = Al(OH) 3 + H +
However sulfides, sulfites, carbonates aluminum and them sour salt hydrolyze irreversibly, fully, i.e. do not exist in aqueous solution, but decomposes with 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 acidic 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.
NaAlO2 break it down into Na 2 O and Al 2 O 3
Then it will become obvious to us that 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 influence of excess water, aluminates transform into complex salts:
KAlO 2 + H 2 O = K
NaAlO 2 + 2H 2 O = Na
Binary compounds
Aluminum sulfide under the influence of nitric acid it is oxidized to sulfate:
Al 2 S 3 + 8HNO 3 → Al 2 (SO 4) 3 + 8NO 2 + 4H 2 O
or to sulfuric acid (under the influence 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 into aluminum hydroxide and methane:
Al 4 C 3 + 12H 2 O → 4Al(OH) 3 + 3CH 4
Aluminum nitride decomposes when exposed to mineral acids on aluminum and ammonium salts:
AlN + 4HCl → AlCl 3 + NH 4 Cl
Also, aluminum nitride decomposes when exposed to water:
AlN + 3H 2 O → Al(OH) 3 ↓ + NH 3
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 solutions of acids gives average aluminum salts, and with solutions of bases - complex salts - metal hydroxyaluminates:
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 produced by the method of reducing metals with aluminum 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 powder - for fire-resistant, chemically resistant and abrasive materials, in the form of crystals - for the production of lasers and synthetic precious stones (rubies, sapphires, etc.), colored with impurities of oxides of other metals - 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 + 3HNO3 = Al(NO3)3 + 3H2O;
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 influence of 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) the action of ammonia hydrate on Al salts; at room temperature Al(OH)3 is formed.
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 and empty spaces in electron orbitals. Elements chromium And molybdenum have an atypical electronic structure - they have one electron in the outer s-orbital (like Nb from the VB subgroup). These elements have 6 electrons in the outer d- and s-orbitals, so all orbitals are half filled, i.e., each has one electron. Having a similar electronic configuration, the element is particularly stable and resistant to oxidation. Tungsten has a stronger metallic bond than molybdenum. The degree of oxidation of elements of the chromium subgroup varies greatly. Under proper conditions, all elements exhibit a positive oxidation number ranging from 2 to 6, with the maximum oxidation number corresponding to the group number. Not all oxidation states of elements are stable; chromium has the most stable one – +3.
All elements form the oxide MVIO3; oxides with lower oxidation states are also known. All elements of this subgroup are amphoteric - they form complex compounds and acids.
Chromium, 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 environment. By removing the film chemically or mechanically, the chemical activity of metals can be increased.
Chromium. The element is obtained from chromite ore Fe(CrO2)2, reducing it with coal: Fe(CrO2)2 + 4C = (Fe + 2Cr) + 4CO?.
Pure chromium is obtained by reduction of Cr2O3 using aluminum or electrolysis of a solution containing chromium ions. By isolating chromium using electrolysis, it is possible to obtain chromium coatings used as decorative and protective films.
Ferrochrome is obtained from chromium, which is used in steel production.
Molybdenum. Obtained from sulfide ore. Its compounds are used in steel production. 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 automobile production.
Tungsten. Obtained from oxide extracted from enriched ore. Aluminum or hydrogen is used as a reducing agent. The resulting tungsten powder is subsequently formed under high pressure and heat treatment (powder metallurgy). In this form, tungsten is used to make filaments and added to steel.