Every day we come across salts and do not even think about the role they play in our lives. But without them, and the water would not be so delicious, and the food would not bring pleasure, and the plants did 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 irreplaceable?
What are salts?
By its composition this is the most numerous class, which is distinguished by its diversity. Back in the 19th century, the chemist J. Werzelius defined the salt as the reaction product between an acid and a base, in which the hydrogen atom is replaced by a metal atom. In water, salts are usually dissociated into a metal or ammonium (cation) and an acid residue (anion).
You can obtain salts in the following ways:
- by the interaction of metal and non-metal, in this case it will be anoxic;
- when the metal interacts with an acid, a salt is obtained and hydrogen is liberated;
- metal can displace another metal from the solution;
- in the interaction of two oxides - acid and basic (they are also called nonmetal oxide and metal oxide, respectively);
- the reaction of metal oxide and acid produces salt and water;
- the reaction between the base and the non-metal oxide also gives salt and water;
- with the help of the ion exchange reaction, different water-soluble substances (bases, acids, salts) can react, but the reaction will proceed if a gas, water or salts are formed that are slightly soluble (insoluble) in water.
Only the chemical composition of the properties of salts and depend. But first, we'll figure it out 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 the interaction with water (soluble, poorly soluble and insoluble).
Such a classification reflects the whole variety of substances not completely. The current and most complete classification, reflecting not only the composition, but also the properties of salts, is presented in the following table.
No matter how wide the class of these substances, but the general physical properties of salts can be distinguished. These are substances of a non-molecular structure, with an ionic crystal lattice.
Very high melting points and boiling points. Under normal conditions all salts do not conduct electricity, but in solution most of them perfectly conduct current.
Color can be very different, it depends on the metal ion, which is part of its composition. Ferrous sulfate (FeSO4 ) - green, ferric chloride (FeCl3 ) - dark red, and potassium chromate (K2 CrO4 ) of a beautiful bright yellow color. But most of the salts are still colorless or white.
The solubility in water also varies and depends on the composition of the ions. In principle, all physical properties of salts have a feature. They depend on the ion of which metal and what acid residue are included in the composition. Let's continue to consider the salts.
Chemical properties of salts
Here too, there is an important feature. Like physical, chemical properties of salts depend on their composition. And also on what class they belong to.
But the general properties of salts can still be distinguished:
- many of them decompose on heating with the formation of two oxides: acid and basic, and anoxic - metal and nonmetal;
- salts interact with other acids, but the reaction occurs only if the acidic residue of a weak or volatile acid is present in the salt composition or as a result an insoluble salt is obtained;
- interaction with alkali is possible if the cation forms an insoluble base;
- a reaction is also possible between two different salts, but only if one of the newly formed salts does not dissolve in water;
- there can be a reaction with the metal, but it is possible only if we take the metal located to the right of the voltage range from the metal contained in the salt.
The chemical properties of salts belonging to normal are discussed above, while other classes react with substances in a somewhat different way. But the difference is only in output products. Basically, all the chemical properties of salts are preserved, as are the requirements for the course of reactions.