Salts in chemistry: types and properties. Salt Formula
In order to answer the question of what salt is, you usually don’t have to think for a long time. This chemical compound is quite common in everyday life. There is no need to talk about ordinary table salt. The detailed internal structure of salts and their compounds is studied by inorganic chemistry.
Salt definition
A clear answer to the question of what salt is can be found in the works of M. V. Lomonosov. He gave this name to fragile bodies that can dissolve in water and do not ignite under the influence of high temperatures or open flames. Later, the definition was derived not from their physical, but from the chemical properties of these substances.
An example of a mixed one is the calcium salt of hydrochloric and hypochlorous acid: CaOCl 2.
Nomenclature
Salts formed by metals with variable valency have an additional designation: after the formula, the valency is written in brackets in Roman numerals. So, there is iron sulfate FeSO 4 (II) and Fe 2 (SO4) 3 (III). In the name of salts there is a prefix hydro-, if there are unsubstituted hydrogen atoms in its composition. For example, potassium hydrogen phosphate has the formula K 2 HPO 4 .
Properties of salts in electrolytes
The theory of electrolytic dissociation gives its own interpretation of chemical properties. In the light of this theory, a salt can be defined as a weak electrolyte that, when dissolved, dissociates (breaks down) in water. Thus, a salt solution can be represented as a complex of positive negative ions, and the first ones are not H + hydrogen atoms, and the second ones are not OH - hydroxo group atoms. There are no ions that would be present in all types of salt solutions, so they do not have any common properties. The lower the charges of the ions that form the salt solution, the better they dissociate, the better the electrical conductivity of such a liquid mixture.
Acid salt solutions
Acid salts in solution decompose into complex negative ions, which are an acid residue, and simple anions, which are positively charged metal particles.
For example, the dissolution reaction of sodium bicarbonate leads to the decomposition of the salt into sodium ions and the rest of HCO 3 -.
The full formula looks like this: NaHCO 3 \u003d Na + + HCO 3 -, HCO 3 - \u003d H + + CO 3 2-.
Solutions of basic salts
The dissociation of basic salts leads to the formation of acid anions and complex cations consisting of metals and hydroxogroups. These complex cations, in turn, are also able to decompose in the process of dissociation. Therefore, in any solution of a salt of the main group, there are OH - ions. For example, the dissociation of hydroxomagnesium chloride proceeds as follows:
Distribution of salts
What is salt? This element is one of the most common chemical compounds. Everyone knows table salt, chalk (calcium carbonate) and so on. Among the carbonate salts, the most common is calcium carbonate. It is an integral part of marble, limestone, dolomite. And calcium carbonate is the basis for the formation of pearls and corals. This chemical compound is essential for the formation of hard integuments in insects and skeletons in chordates.
Salt has been known to us since childhood. Doctors warn against its excessive use, but in moderation it is essential for the implementation of vital processes in the body. And it is needed to maintain the correct composition of the blood and the production of gastric juice. Saline solutions, an integral part of injections and droppers, are nothing more than a solution of table salt.
The solubility table of salts, acids and bases is the foundation, without which it is impossible to fully master chemical knowledge. The solubility of bases and salts helps in teaching not only schoolchildren, but also professional people. The creation of many life products cannot do without this knowledge.
Table of solubility of acids, salts and bases in water
The table of solubility of salts and bases in water is a manual that helps in mastering the basics of chemistry. The following notes will help you understand the table below.
- P - indicates a soluble substance;
- H is an insoluble substance;
- M - the substance is slightly soluble in the aquatic environment;
- RK - a substance can dissolve only when exposed to strong organic acids;
- The dash will say that such a creature does not exist in nature;
- NK - does not dissolve in either acids or water;
- ? - a question mark indicates that today there is no exact information about the dissolution of the substance.
Often, the table is used by chemists and schoolchildren, students for laboratory research, during which it is necessary to establish the conditions for the occurrence of certain reactions. According to the table, it turns out to find out how the substance behaves in a hydrochloric or acidic environment, whether a precipitate is possible. Precipitate during research and experiments indicates the irreversibility of the reaction. This is a significant point that can affect the course of the entire laboratory work.
A salt can be defined as a compound that is formed by the reaction between an acid and a base, but is not water. In this section, those properties of salts that are associated with ionic equilibria will be considered.
salt reactions in water
Somewhat later it will be shown that solubility is a relative concept. However, for the purposes of the following discussion, we can roughly classify all salts into water-soluble and water-insoluble salts.
Some salts, when dissolved in water, form neutral solutions. Other salts form acidic or alkaline solutions. This is due to the occurrence of a reversible reaction between salt ions and water, as a result of which conjugate acids or bases are formed. Whether a salt solution is neutral, acidic, or alkaline depends on the type of salt. In this sense, there are four types of salts.
Salts formed by strong acids and weak bases. Salts of this type, when dissolved in water, form an acidic solution. Let's take ammonium chloride NH4Cl as an example. When this salt is dissolved in water, the ammonium ion acts as
The excess amount of H3O+ ions formed in this process determines the acidic properties of the solution.
Salts formed by a weak acid and a strong base. Salts of this type, when dissolved in water, form an alkaline solution. As an example, let's take sodium acetate CH3COONa1 The acetate ion acts as a base, accepting a proton from water, which in this case acts as an acid:
An excess of OH- ions formed in this process determines the alkaline properties of the solution.
Salts formed by strong acids and strong bases. When salts of this type are dissolved in water, a neutral solution is formed. Let's take sodium chloride NaCl as an example. When dissolved in water, this salt is completely ionized, and, therefore, the concentration of Na+ ions is equal to the concentration of Cl- ions. Since neither ion enters into acid-base reactions with water, there is no formation of an excess amount of H3O + or OH ions in the solution. Therefore, the solution is neutral.
Salts formed by weak acids and weak bases. An example of salts of this type is ammonium acetate. When dissolved in water, the ammonium ion reacts with water as an acid, and the acetate ion reacts with water as a base. Both of these reactions are described above. An aqueous solution of a salt formed by a weak acid and a weak base can be weakly acidic, slightly alkaline, or neutral, depending on the relative concentrations of H3O+ and OH- ions formed as a result of the reactions of cations and anions of the salt with water. It depends on the ratio between the values of the dissociation constants of the cation and anion.
Water is one of the main chemical compounds on our planet. One of its most interesting properties is the ability to form aqueous solutions. And in many areas of science and technology, the solubility of salt in water plays an important role.
Solubility is understood as the ability of various substances to form homogeneous (homogeneous) mixtures with liquids - solvents. It is the volume of the material that is used to dissolve and form a saturated solution that determines its solubility, comparable to the mass fraction of this substance or its amount in a concentrated solution.
According to their ability to dissolve, salts are classified as follows:
- soluble substances include substances that can be dissolved in 100 g of water more than 10 g;
- sparingly soluble are those whose amount in the solvent does not exceed 1 g;
- the concentration of insoluble in 100 g of water is less than 0.01.
In the case when the polarity of the substance used for dissolution is similar to the polarity of the solvent, it is soluble. At different polarities, most likely, it is not possible to dilute the substance.
How dissolution occurs
If we talk about whether salt dissolves in water, then for most salts this is a fair statement. There is a special table according to which you can accurately determine the amount of solubility. Since water is a universal solvent, it mixes well with other liquids, gases, acids and salts.
One of the clearest examples of the dissolution of a solid in water can be observed almost every day in the kitchen, while preparing dishes using table salt. So why does salt dissolve in water?
From the school chemistry course, many remember that the molecules of water and salt are polar. This means that their electrical poles are opposite, which results in a high dielectric constant. Water molecules surround ions of another substance, for example, as in our case, NaCl. In this case, a liquid is formed, which is homogeneous in its consistency.
Temperature effect
There are several factors that affect the solubility of salts. First of all, this is the temperature of the solvent. The higher it is, the greater is the value of the diffusion coefficient of particles in the liquid, and the mass transfer occurs faster.
Although, for example, the solubility of common salt (NaCl) in water practically does not depend on temperature, since its solubility coefficient is 35.8 at t 20 ° C and 38.0 at 78 ° C. But copper sulfate (CaSO4) with increasing temperature water dissolves worse.
Other factors that affect solubility include:
- The size of the dissolved particles - with a larger area of phase separation, the dissolution occurs faster.
- A mixing process that, when performed intensively, contributes to a more efficient mass transfer.
- The presence of impurities: some accelerate the dissolution process, while others, hindering diffusion, reduce the rate of the process.
Video about the mechanism of salt dissolution
