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Double salts: examples and names

Salts are divided into medium, acidic, basic, double and mixed. All of them are widely used in everyday life, but even more - in industry. Understanding the classification of salts makes it possible to understand the basics of chemistry.

How to classify salts

To begin with, let us define salts. They are chemical compounds in which a metal atom is connected to the acid residue. Unlike other classes of substances, ionic chemical bonds are characteristic for salts.

Representatives of this class are divided into several groups that have specific features.

Normal salts

The average salts in their composition have only cations of a certain metal and an acid residue. As an example of such compounds, mention may be made of sodium chloride, potassium sulfate. It is this group that is considered the most common in the earth's crust. Among the methods for their preparation, we note the neutralization process carried out between the acid and the base.

Acid Salts

This group of compounds consists of metal, hydrogen, and also an acid residue. Polybasic acids form such compounds : phosphoric, sulfuric, and coal. As an example of acidic salt, which is widely used in everyday life, it is possible to mention sodium bicarbonate (baking soda). Such substances are obtained by the interaction between the middle salt and the acid.

Basic salts

In these compounds, metal cations, a hydroxyl group, and anions of the acid residue are present. An example of a basic salt is calcium hydroxochloride.

Mixed salts

Double salts imply the presence of two metals that replace hydrogen in acid. The formation of substances of a similar composition is characteristic of polybasic acids. For example, in potassium carbonate, two active metals are present at once. Double mixed salts are important for the chemical industry, widely used in everyday life.

Features of mixed salts

Double salts of potassium and sodium are found in nature in the form of sylvinite. Also, potassium is able to form mixed salts with aluminum.

Mixed (double) salts are compounds that consist of different anions or cations. For example, bleach in its composition has an anion of hypochlorous and hydrochloric acid.

Of particular interest are the double ammonium salts. Most of the substances obtained are used as mineral fertilizers.

The production of double ammonium salts is carried out by the interaction of ammonia with polybasic acids. Diammonium phosphates are in demand in the manufacture of fire retardants (flame retardants). Double salts that do not contain impurities are necessary in the pharmaceutical and food industries.

Ammonium zinc, magnesium phosphates are of industrial importance. Due to insubstantial solubility in water, such salts serve as fire retardants in paints and plastics.

These double salts are suitable for impregnating fabrics and wood, protecting the surfaces from high humidity. Iron and aluminum ammonium phosphates are an excellent tool for protecting metal structures from natural corrosion processes.

Examples of double salts having technical significance can be cited for iron and zinc. They are a breeding ground for growing yeast, are in demand in the manufacture of matches, the production of insulating materials, and mica.


Double ammonium salts are obtained by thermal saturation of phosphoric acid with ammonia and a certain alkali. Industrial interest is dimmonium phosphate. It is produced by heat treatment with ammonia phosphoric acid. For the successful course of the process, a temperature of about 70 degrees Celsius is required. The technology assumes the formation in the form of precipitation of aluminum and iron phosphates, which also find their industrial application.

Some complications arise with the names of double salts due to the fact that they contain both acidic residue and two cations.

Magnesium ammonium phosphate is in demand in the chemical industry, therefore the technology of its creation has certain features. The extraction phosphoric acid, which is mixed with magnesium phosphate, is neutralized with gaseous ammonia.

Complex compounds

Between complex and double salts there are certain differences. Let's try to find out the features of complex salts. In their composition, the presence of a complex ion is envisaged, which consists of square brackets. In addition, in such compounds there is a complexing agent (central ion). It is surrounded by particles called ligands. For complex salts, stepwise dissociation is characteristic. The first stage is the formation of a complex ion in the form of a cation or anion. Further, there is a partial dissociation of the complex ion into a cation and ligands.

Features of the nomenclature of salts

Considering that there are many different types of salts, their nomenclature is of interest. For medium salts, the name is formed on the basis of an anion (chloride, sulfate, nitrate), to which the Russian name of the metal is added. For example, CaCO3 is calcium carbonate.

For acid salts, the addition of a hydro-. For example, KHCO3-potassium hydrogen carbonate.

The nomenclature of basic salts implies the use of the prefix hydroxy-. Thus, the salt Al (OH) 2Cl is called aluminum dihydroxychloride.

When the name of double salts containing two cations is given, it is first necessary to give the name to the anion, then to list both metals entering the compound.

More complex names are characteristic of complex compounds. In chemistry, there is a special section that deals with the study of such salts.

If we analyze the physical properties of different representatives of double salts, it can be noted that they differ significantly in their ability to dissolve in water. Among the double salts are examples of substances that have good solubility, for example, sodium chloride, potassium. Among the sparingly soluble compounds, double salts of phosphoric and silicic acid can be cited.

By chemical properties, double salts are analogous to normal (average), capable of interacting with acids, other salts.

Nitrates and ammonium salts undergo thermal decomposition, forming several reaction products.

In the case of electrolytic dissociation of such compounds, it is possible to obtain residue anions and metal cations. For example, in the decomposition of alumokalic alum into ions , aluminum and potassium cations, as well as sulfate ions, can be found in the solution.

Separation of a mixture of salts

Considering that two metals are contained in natural minerals, there is a need for their separation. Among the many methods that allow the separation of salt mixtures, it is possible to isolate fractional crystallization. This method involves pre-melting the double salt, then dividing it into different compounds, then crystallizing. Such an option for the separation of mixtures is related to the physical characteristics of the substances. When the mixture is separated by chemical methods, reagents are selected that are qualitative for certain cations or anions. After precipitation of some parts of double salt, the precipitate is removed.

If it is necessary to separate the three-component system, in which there is a solid phase, and also emulsions are present, centrifugation is carried out.


Double salts differ from the other types of salts by the presence of two metals in the formula. In pure form, such compounds are rarely used, mainly they are initially separated by physical or chemical methods, and only then are they used in various spheres of industrial production. Double salts are also used in the chemical industry as a source of obtaining a lot of demanded chemicals.

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