Mg, (OH)2 + H, Cl = Mg, OH, Cl + H2O.
Magnesium, hydroxyl, and chlorine ions are left at the close of the reaction, and under the proper conditions unite to form molecules of the compound Mg(OH)Cl. This compound, when dissolved, can form hydroxyl ions and therefore possesses basic properties; it can also form the ions of a salt (Mg and Cl), and has properties characteristic of salts. Substances of this kind are called basic salts.
DEFINITION: A basic salt is a substance which can give the ions both of a base and of a salt when dissolved in water.
2. Acid salts. In a similar way, when sulphuric acid and sodium hydroxide are brought together in the ratio of equal numbers of the molecules of each, it is possible to have a reaction expressed by the equation
Na, OH + H2, SO4 = Na, H, SO4 + H2O.
The ions remaining after all the hydroxyl ions have been used up are those of an acid (H) and those of a salt (Na and SO4). These unite to form the substance NaHSO4, and as the solution becomes saturated with this substance through evaporation, it separates in the form of crystals. In solution this substance can give hydrogen ions, and therefore possesses acid properties; it can also give the ions characteristic of a salt. It is therefore called an acid salt.
DEFINITION: An acid salt is one which can give the ions of an acid and of a salt when in solution.
3. Normal salts. Salts which are the products of complete neutralization, such as Na2SO4, and which in solution can give neither hydrogen nor hydroxyl ions, but only the ions of a salt, are called normal salts to distinguish them from acid and basic salts.
Methods of expressing reactions between compounds in solution. Chemical equations representing reactions between substances in solution may represent the details of the reaction, or they may simply indicate the final products formed. In the latter case the formation of ions is not indicated. Thus, if we wish to call attention to the details of the reaction between sodium hydroxide and hydrochloric acid in solution, the equation is written as follows:
Na+, OH- + H+, Cl- = Na+, Cl- + H2O.