Chemistry of aluminum. The most important compounds of aluminum The chemical formula of aluminum hydroxide

Inorganic substance, aluminum alkali, formula Al(OH) 3 . Occurs in nature, is part of bauxites.

Properties

It exists in four crystalline modifications and in the form of a colloidal solution, a gel-like substance. The reagent is almost insoluble in water. Does not burn, does not explode, is not poisonous.

In solid form, it is a finely crystalline loose powder, white or transparent, sometimes with a slight gray or pink tinge. The gel-like hydroxide is also white.

The chemical properties of the solid and gel-like modifications are different. The solid substance is quite inert, does not react with acids, alkalis, other elements, but can form metaaluminates as a result of fusion with solid alkalis or carbonates.

The gel-like substance exhibits amphoteric properties, that is, it reacts with both acids and alkalis. In the reaction with acids, aluminum salts of the corresponding acid are formed, with alkalis - salts of another type, aluminates. Does not react with ammonia solution.

When heated, the hydroxide decomposes into oxide and water.

Precautionary measures

The reagent belongs to the fourth hazard class, is considered fireproof and practically safe for humans and the environment. Caution should be exercised only with aerosol particles in the air: dust has an irritating effect on the respiratory system, skin, and mucous membranes.

Therefore, in workplaces where large amounts of aluminum hydroxide dust can be generated, employees should wear respiratory, eye and skin protection. It is necessary to establish control over the content of harmful substances in the air of the working area according to the methodology approved by GOST.

The room should be equipped with supply and exhaust ventilation, and, if necessary, with local aspiration suction.

Store solid aluminum hydroxide in multilayer paper bags or other containers for bulk products.

Application

In industry, the reagent is used to obtain pure aluminum and aluminum derivatives, for example, aluminum oxide, sulfate and aluminum fluoride.
- Aluminum oxide obtained from hydroxide is used to obtain artificial rubies for the needs of laser technology, corundum - for air drying, purification of mineral oils, for the production of emery.
- In medicine, it is used as an enveloping agent and a long-acting antacid to normalize the acid-base balance of the human gastrointestinal tract, to treat gastric and duodenal ulcers, gastroesophageal reflux and some other diseases.
- In pharmacology, it is part of vaccines to enhance the body's immune response to the effects of an introduced infection.
- In water treatment - as an adsorbent that helps to remove various contaminants from water. Hydroxide actively reacts with substances to be removed, forming insoluble compounds.
- In the chemical industry, it is used as an environmentally friendly fire retardant for polymers, silicones, rubbers, paints and varnishes - to worsen their combustibility, flammability, suppress the release of smoke and toxic gases.
- In the production of toothpaste, mineral fertilizers, paper, dyes, cryolite.

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 will require 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 variants of chemical reactions of 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 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).

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 as a result of the 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.

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 the 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 represented as a finely crystalline white powder. The presence of pink and gray shades is acceptable.

The chemical formula of the compound is Al(OH)3. The compound and water form the hydroxide of which is also determined in many respects by the elements that make up its composition. This compound is obtained by carrying out the reaction of the interaction of an aluminum salt and a dilute alkali, while their excess should not be allowed. The precipitate of aluminum hydroxide obtained during this reaction can then react with acids.

Aluminum hydroxide interacts with an aqueous solution of rubidium hydroxide, an alloy of this substance, cesium hydroxide, cesium carbonate. In all cases, water is released.

Aluminum hydroxide has an equal 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 interacts with acids, and as a result of the reactions, medium salts are obtained and water is released. Upon entering into reactions 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 shows acidic and basic properties when interacting with and also with alkalis. In these reactions, when hydroxide is dissolved in acids, hydroxide ions are split off, and when interacting with alkali, a hydrogen ion is split off. To see this, you can, for example, conduct a reaction in which aluminum hydroxide is involved. To carry it out, you need to pour a little aluminum filings into a test tube and pour a small amount of sodium hydroxide, not more than 3 milliliters. The test tube should be tightly closed with a stopper, and slow heating should be started. After that, fixing the test tube on a tripod, it is necessary to collect the released hydrogen in another test tube, after putting 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, in the same case, if air gets into it, cotton will occur.

Aluminum hydroxide is obtained in laboratories in several ways:

By the reaction of the interaction of 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 action of ammonia hydrate on aluminum salts.

Industrial production is associated with the processing of bauxite. Technologies of impact on aluminate solutions with carbonates are also used.

Aluminum hydroxide is used in the manufacture of mineral fertilizers, cryolite, various medical and pharmacological preparations. In chemical production, the substance is used to produce aluminum fluoride and sulfide. The connection is indispensable 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, high acidity of the body, peptic ulcers.

When handling the substance, one should be careful not to inhale its vapors, as they cause severe lung damage. Being a weak laxative, it is dangerous in large doses. Corrosion causes aluminosis.

The substance itself is quite safe, as it does not react with oxidizing agents.

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). The content in the earth's crust is 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 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. You can learn more about the acceptance of aluminum for processing, as well as the current prices for this type of metal. .

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 the 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 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 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 - 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 weight - 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 the 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, with 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.