Many active metal oxides, such as potassium, sodium, or lithium oxides , can interact with water. In this case, compounds related to hydroxides are found in the reaction products. The properties of these substances, especially the occurrence of chemical processes in which the bases participate, are due to the presence of a hydroxyl group in their molecules. So, in electrolytic dissociation reactions, the bases are split into metal ions and OH - anions. How bases interact with non-metal oxides, acids and salts, we will consider in our article.
The nomenclature and structure of the molecule
To correctly name the base, it is required to add the word hydroxide to the name of the metal element. We give specific examples. Aluminum base refers to amphoteric hydroxides, the properties of which we will consider in the article. The mandatory presence in the base molecules of a hydroxyl group bound to the metal cation by the ionic type of bond can be determined using indicators, for example, phenolphthalein. In an aqueous medium, an excess of OH - ions is determined by a change in the color of the indicator solution: colorless phenolphthalein becomes raspberry. If a metal exhibits several valencies, it may form several bases. For example, iron has two bases in which the valency of the metal is 2 or 3. The first compound is characterized by the signs of basic hydroxides, the second by amphoteric ones. Therefore, the properties of higher hydroxides differ from compounds in which the metal has a lower degree of valency.
Physical characteristic
Bases are heat resistant solids. In relation to water, they are divided into soluble (alkali) and insoluble. The first group is formed by chemically active metals - elements of the first and second groups. Water-insoluble substances are composed of atoms of other metals, whose activity is inferior to sodium, potassium or calcium. Examples of such compounds are iron or copper bases. The properties of hydroxides will depend on which group of substances they belong to. So, alkalis are thermally strong and do not decompose when heated, whereas water-insoluble bases under the influence of high temperature are destroyed, forming oxide and water. For example, a copper base is decomposed as follows:
Cu (OH) 2 = CuO + H 2 O
Chemical properties of hydroxides
The interaction between two of the most important groups of compounds - acids and bases - is called a neutralization reaction in chemistry. This name can be explained by the fact that chemically aggressive hydroxides and acids form neutral products - salts and water. Being, in fact, an exchange process between two complex substances, neutralization is characteristic both for alkalis and for water-insoluble bases. We give the equation of the neutralization reaction between potassium hydroxide and perchloric acid:
KOH + HCl = KCl + H 2 O
An important property of alkali metal bases is their ability to react with acid oxides; as a result, salt and water can be obtained. For example, passing carbon dioxide through sodium hydroxide, you can get its carbonate and water:
2NaOH + CO 2 = Na 2 CO 3 + H 2 O
The ion exchange reactions include the interaction between alkalis and salts, which proceeds with the formation of insoluble hydroxides or salts. So, pouring a solution of sodium hydroxide dropwise into a solution of copper sulfate, you can get a blue jelly-like precipitate. This is a copper base insoluble in water:
CuSO 4 + 2NaOH = Cu (OH) 2 + Na 2 SO 4
The chemical properties of hydroxides that are insoluble in water differ from alkalis in that they lose water with little heating - they dehydrate, turning into the form of the corresponding basic oxide.
Bases exhibiting dual properties
If an element or a complex substance can react with both acids and alkalis, it is called amphoteric. These include, for example, zinc, aluminum and their bases. The properties of amphoteric hydroxides make it possible to write down their molecular formulas both in the form of bases, while isolating the hydroxo group, and in the form of acids. We present several equations for the reactions of an aluminum base with perchloric acid and sodium hydroxide. They illustrate the special properties of hydroxides related to amphoteric compounds. The second reaction occurs with the decomposition of alkali:
2Al (OH) 3 + 6HCl = 2AlCl 3 + 3H 2 O
Al (OH) 3 + NaOH = NaAlO 2 + 2H 2 O
The products of the processes are water and salts: aluminum chloride and sodium aluminate. All amphoteric bases are not soluble in water. They are mined as a result of the interaction of the corresponding salts and alkalis.
Methods of preparation and application
In industry, requiring large volumes of alkalis, they are obtained by electrolysis of salts containing active metal cations of the first and second groups of the periodic system. The raw material for the extraction, for example, sodium hydroxide, is a solution of sodium chloride. The reaction equation will be as follows:
2NaCl + 2H 2 O = 2NaOH + H 2 + Cl 2
The base of inactive metals in the laboratory is obtained by the interaction of alkalis with their salts. The reaction refers to the type of ion exchange and ends with the precipitation of the base. A simple way to produce alkalis is a substitution reaction that takes place between the active metal and water. It is accompanied by heating of the reacting mixture and refers to the exothermic type.
The properties of hydroxides are used in industry. A special role here is played by alkalis. They are used as purifiers for kerosene and gasoline, for soap, natural leather processing, as well as in the technologies for the production of artificial silk and paper.