Properties of salts: physical and chemical
Every day we are confronted with salts and do not even think about the role they play in our life. But without them, the water would not be so tasty, and food would not bring pleasure, and the plants would not grow, and life on earth could not exist if there were no salt in our world. So what are these substances and what properties of salts make them indispensable?
What is salt
In composition, it is the most numerous class, distinguished by diversity. As early as the 19th century, chemist J. Vercelius defined salt as a product of the reaction between an acid and a base, in which a hydrogen atom is replaced by a metallic one. In water, salts are usually dissociated into a metal or ammonium (cation) and an acid residue (anion).
You can get salt in the following ways:
- by the interaction of metal and non-metal, in this case, it will be oxygen-free;
- when a metal interacts with an acid, salt is obtained and hydrogen is released;
- the metal may displace another metal from the solution;
- in the interaction of two oxides of acid and basic (also called non-metal oxide and metal oxide, respectively)
- the reaction of the metal oxide and the acid produces salt and water;
- the reaction between the base and the non-metal oxide also gives salt and water;
- using an ion exchange reaction, various water-soluble substances (bases, acids, salts) can react, but the reaction will occur if gas, water or slightly soluble (insoluble) salts form in water.
The properties of the salts depend only on the chemical composition. But for the beginning we will understand in their classes.
Depending on the composition, the following classes of salts are distinguished:
- on the content of oxygen (oxygen-containing and oxygen-free);
- on interaction with water (soluble, poorly soluble and insoluble).
Such a classification does not fully reflect the diversity of substances. The modern and most complete classification, reflecting not only the composition, but also the properties of salts, is presented in the following table.The salt
|Hydrogen is completely replaced||Hydrogen atoms replaced by metalnot completely||Base groups are replaced by an incomplete acid residue.||Composed of two metals and one acid residue||Composed of one metal and two acid residue||Complex substances consisting of a complex cation and anion or cation and a complex anion|
However wide the class of these substances may be, it is possible to single out the general physical properties of the salts. These are substances of non-molecular structure, with an ionic crystal lattice.
Very high melting and boiling points. Under normal conditions, all salts do not conduct electricity, but most of them are perfectly conductive in solution.
The color can be very different, it depends on the metal ion, which is part of it. Ferrous sulfate (FeSO4) - green, ferric chloride (FeCl3) - dark red, and potassium chromate (K2Cro4) beautiful bright yellow. But most salts are still colorless or white.
Solubility in water also varies and depends on the composition of ions. In principle, all physical properties of salts have a feature. They depend on which metal ion and which acid residue is included in the composition. We continue to consider salt.
Chemical properties of salts
Here, too, there is an important feature. As well as physical, chemical properties of salts depend on their composition. And also on which class they belong to.
But the general properties of salts can still be distinguished:
- many of them decompose when heated to form two oxides: acid and base, and oxygen-free - metal and non-metal;
- salts also interact with other acids, but the reaction proceeds only if the salt contains an acidic residue of a weak or volatile acid, or the result is an insoluble salt;
- interaction with alkali is possible if the cation forms an insoluble base;
- a reaction is possible between two different salts, but only if one of the newly formed salts does not dissolve in water;
- a reaction may occur with the metal, but it is possible only if we take the metal located to the right in the voltage row from the metal contained in the salt.
The chemical properties of normal salts are discussed above, while other classes react with substances in a slightly different way. But the difference is only on the products at the outlet. Basically, all the chemical properties of salts are preserved, as are the requirements for the course of reactions.