Aluminum hydroxide, characteristics, properties and production, chemical reactions. The most important aluminum compounds Signs of the decomposition reaction of aluminum hydroxide

Aluminum hydroxide is a chemical substance that is a combination of aluminum oxide with water. It can be in liquid and solid states. Liquid hydroxide is a jelly-like transparent substance that is very poorly soluble in water. Solid hydroxide is a white crystalline substance that has passive chemical properties and does not react with almost any other element or compound.

Obtaining aluminum hydroxide

The production of aluminum hydroxide occurs due to a chemical exchange reaction. To do this, use an aqueous solution of ammonia and some aluminum salt, most often aluminum chloride. Thus, a liquid substance is obtained. If solid hydroxide is needed, carbon dioxide is passed through the dissolved alkali of sodium tetrahydroxodiquaaluminate. Many lovers of experiments are concerned about the question of how to get aluminum hydroxide at home? To do this, it is enough to purchase the necessary reagents and chemical glassware in a specialized store.

To obtain a solid, you will also need special equipment, so it is better to stop at the liquid version. When carrying out the reaction, it is necessary to use a well-ventilated room, since one of the by-products may be a gas or a substance with a pungent odor, which can adversely affect the well-being and human health. It is worth working in special protective gloves, since most acids cause chemical burns when they come into contact with the skin. It will not be superfluous to take care of eye protection in the form of special glasses. When starting any business, first of all, you need to think about safety!

Freshly synthesized aluminum hydroxide reacts with most active acids and alkalis. That is why ammonia water is used to obtain it in order to keep the formed substance in its pure form. When used to produce acid or alkali, it is necessary to calculate the proportion of elements as accurately as possible, otherwise, in excess, the resulting aluminum hydroxide interacts with the remains of the unabsorbed base and completely dissolves in it. This is due to the high level of chemical activity of aluminum and its compounds.

Basically, aluminum hydroxide is obtained from bauxite ore with a high content of metal oxide. The procedure allows you to quickly and relatively cheaply separate useful elements from waste rock. The reactions of aluminum hydroxide with acids lead to the reduction of salts and the formation of water, and with alkalis - to the production of complex hydroxoaluminum salts. Solid hydroxide is combined with solid alkalis by fusion to form metaaluminates.

Basic properties of matter

Physical properties aluminum hydroxide: density - 2.423 grams per cubic centimeter, solubility in water - low, color - white or transparent. The substance can exist in four polymorphic variants. Under the influence of low temperatures, an alpha hydroxide is formed, called bayerite. Under the influence of heating, gamma hydroxide or gibbsite can be obtained. Both substances have a crystal molecular lattice with hydrogen intermolecular bond types. There are also two more modifications - beta hydroxide or nordstandrite and triclinic gibbsite. The first is obtained by calcining bayerite or gibbsite. The second differs from other types in the triclinic, and not in the monotonous structure of the crystal lattice.

Chemical properties aluminum hydroxide: molar mass- 78 mol, in a liquid state it dissolves well in active acids and alkalis, decomposes when heated, has amphoteric features. In industry, in the overwhelming majority of cases, it is liquid hydroxide that is used, since thanks to high level chemical activity, it is easy to process and does not require the use of catalysts or special conditions the course of the reaction.

The amphoteric nature of aluminum hydroxide is manifested in the duality of its nature. This means that under various conditions it can exhibit acidic or alkaline properties. When the hydroxide reacts as an alkali, a salt is formed in which aluminum is a positively charged cation. Acting as an acid, aluminum hydroxide also forms a salt at the outlet. But in this case, the metal already plays the role of a negatively charged anion. The dual nature opens up wide possibilities for the use of this chemical compound. It is used in medicine for the manufacture of drugs prescribed for violations of the acid-base balance in the body.

Aluminum hydroxide is included in vaccines as a substance that enhances the body's immune response to an irritant. The insolubility of the aluminum hydroxide precipitate in water allows the substance to be used for water treatment purposes. The chemical compound is a very strong adsorbent, which allows you to extract a large amount of harmful elements from the composition of water.

Application in industry

The use of hydroxide in industry is associated with the production of pure aluminum. The technological process begins with the processing of ore containing aluminum oxide, which, upon completion of the process, turns into hydroxide. The yield of products in this reaction is high enough that after completion, almost bare rock remains. Next, the operation of decomposition of aluminum hydroxide is carried out.

The procedure does not require special conditions, since the substance decomposes well when heated to temperatures above 180 degrees Celsius. This step makes it possible to isolate the alumina. This compound is a base or auxiliary material for the manufacture of a large number of industrial and household products. If it is necessary to obtain pure aluminum, the electrolysis process is used with the addition of sodium cryolite to the solution. The catalyst takes oxygen from the oxide, and pure aluminum is deposited on the cathode.

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, 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. Other amphoteric hydroxides, such as iron or beryllium hydroxide, also have the properties described above.

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.

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 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.

Aluminum hydroxide, characteristics, properties and production, chemical reactions.

Aluminum hydroxide - inorganic matter, It has chemical formula Al(OH)3.

Brief characteristic of aluminum hydroxide:

aluminum hydroxide is a white inorganic substance.

Chemical formula of aluminum hydroxide Al(OH)3.

Poorly soluble in water.

It has the ability to adsorb various substances.

Modifications of aluminum hydroxide:

There are 4 known crystalline modifications of aluminum hydroxide: gibbsite, bayerite, doyleite and nordstrandite.

Gibbsite is designated as the γ-form of aluminum hydroxide, and bayerite is designated as the α-form of aluminum hydroxide.

Gibbsite is the most chemically stable form of aluminum hydroxide.

Physical properties of aluminum hydroxide:

Parameter name:	Meaning:
Chemical formula	Al(OH)3
Synonyms and names foreign language for aluminum hydroxide α-form	potassium hydroxide aluminum hydroxide α-form bayerite (rus.)
Synonyms and foreign language names for γ-form aluminum hydroxide	potassium hydroxide aluminum hydroxide aluminum hydroxide hydrargillite gibbsite (rus.) hydrargillite (Russian)
Substance type	inorganic
Appearance of α-form aluminum hydroxide	colorless monoclinic crystals
Appearance of γ-form aluminum hydroxide	white monoclinic crystals
Colour	white, colorless
Taste	—*
Smell	—
Aggregate state (at 20 °C and atmospheric pressure 1 atm.)	solid
Density of γ-form aluminum hydroxide (state of matter - solid, at 20 ° C), kg / m 3	2420
Density of γ-form aluminum hydroxide (state of matter - solid, at 20 ° C), g / cm 3	2,42
Decomposition temperature of α-form aluminum hydroxide, °C	150
Decomposition temperature of γ-form aluminum hydroxide, °C	180
Molar mass, g/mol	78,004

* Note:

- there is no data.

Obtaining aluminum hydroxide:

Aluminum hydroxide is obtained as a result of the following chemical reactions:

1. as a result of the interaction of aluminum chloride and sodium hydroxide :

AlCl 3 + 3NaOH → Al(OH) 3 + 3NaCl.

Aluminum hydroxide is also obtained by the interaction of aluminum salts with aqueous solutions of alkali, avoiding their excess.

2. as a result of the interaction of aluminum chloride, sodium carbonate and water:

2AlCl 3 + 3Na 2 CO 3 + 3H 2 O → 2Al(OH) 3 + 3CO 2 + 6NaCl.

In this case, aluminum hydroxide precipitates in the form of a white gelatinous precipitate.

Aluminum hydroxide is also obtained by the interaction of water-soluble salts aluminum with alkali metal carbonates.

Chemical properties of aluminum hydroxide. Chemical reactions of aluminum hydroxide:

Aluminum hydroxide has amphoteric properties, that is, it has both basic and acidic properties.

The chemical properties of aluminum hydroxide are similar to those of hydroxides of other amphoteric metals. Therefore, it is characterized by the following chemical reactions:

1.reaction of aluminum hydroxide with sodium hydroxide:

Al(OH) 3 + NaOH → NaAlO 2 + 2H 2 O (t = 1000 °C),

Al(OH) 3 + 3NaOH → Na 3,

Al(OH) 3 + NaOH → Na.

As a result of the reaction, in the first case, sodium aluminate and water are formed, in the second, sodium hexahydroxoaluminate, and in the third, sodium tetrahydroxoaluminate. In the third case, as sodium hydroxide

2. reaction of aluminum hydroxide with potassium hydroxide:

Al(OH) 3 + KOH → KAlO 2 + 2H 2 O (t = 1000 °C),

Al(OH) 3 + KOH → K.

As a result of the reaction, in the first case, potassium aluminate and water are formed, in the second, potassium tetrahydroxoaluminate. In the second case, as potassium hydroxide concentrated solution is used.

3. reaction of aluminum hydroxide with nitric acid:

Al(OH) 3 + 3HNO 3 → Al(NO 3) 3 + 3H 2 O.

As a result of the reaction, aluminum nitrate and water.

Aluminum hydroxide reacts similarly with other acids.

4. reaction of aluminum hydroxide with hydrogen fluoride:

Al(OH) 3 + 3HF → AlF 3 + 3H 2 O,

6HF + Al(OH) 3 → H 3 + 3H 2 O.

As a result of the reaction, aluminum fluoride and water are formed in the first case, and hydrogen hexafluoroaluminate and water are formed in the second. In this case, in the first case, hydrogen fluoride is used as a starting material in the form of a solution.

5. reaction of aluminum hydroxide with hydrogen bromide:

Al(OH) 3 + 3HBr → AlBr 3 + 3H 2 O.

The reaction produces aluminum bromide and water.

6. reaction of aluminum hydroxide with hydrogen iodine:

Al(OH) 3 + 3HI → AlI 3 + 3H 2 O.

The reaction produces aluminum iodide and water.

7. reaction of thermal decomposition of aluminum hydroxide:

Al(OH) 3 → AlO(OH) + H 2 O (t = 200 °C),

2Al(OH) 3 → Al 2 O 3 + 3H 2 O (t = 575 °C).

As a result of the reaction, in the first case, aluminum metahydroxide and water are formed, in the second, aluminum oxide and water.

8. reaction of aluminum hydroxide and sodium carbonate:

2Al(OH) 3 + Na 2 CO 3 → 2NaAlO 2 + CO 2 + 3H 2 O.

As a result of the reaction, sodium aluminate, carbon monoxide (IV) and water are formed.

10. reaction of aluminum hydroxide and calcium hydroxide:

Ca (OH) 2 + 2Al (OH) 3 → Ca 2.

The reaction produces calcium tetrahydroxoaluminate.

Applications and uses of aluminum hydroxide:

Aluminum hydroxide is used in water treatment (as an adsorbent), in medicine, as a filler in toothpaste (as an abrasive), plastics and plastics (as a fire retardant).