Silicic acid is theoretically a compound of silicon oxide and water. Moreover, the ratio of these components can be very diverse. Therefore, in general terms, their composition can be represented by the formula. In this case, silicic acids with the presence of different amounts of silicon oxide and water, that is, with different values of the parameters n and m, can easily pass from one state to another. Thus, n and m in this case can be considered as variables.
Theoretically, silicic acid can be obtained by reacting a silicate of one of the alkali metals (for example, sodium) and one of the "strong" acids (for example, hydrochloric). In this way, in the free state, some of the following acids were isolated (obtained): metasilicic, orthosilicic, and others. For example, a chemical reaction for the production of metasilicic acid:
+ 2HCl = + 2NaCl
However, it is almost impossible to obtain silicic acid in its pure form. In aqueous solutions (and they are supersaturated), silicic acid as a result of the polymerization process becomes the basis for the formation of colloidal solutions having a rather short period of existence. Further, a gel is formed from these solutions as a result of coagulation. This is the use of silicic acid, as having dried this gel, you get the so-called silica gel, which is used as a desiccant and absorbent. In addition, using special stabilizers, stable colloids (or sols) are obtained from colloidal solutions, which also find application in production.
Silicic acid is sparingly soluble, weak and thermally unstable. When heated, decomposition of silicic acid occurs, which is expressed by the following chemical reaction:
=
It is also a weaker acid than the same carbonic acid. Due to this, silicic acid in aqueous solutions is displaced by carbonic acid from its various salts. As an example, this can be seen in the reaction:
= +
Silicic acid salts are called silicates. They are very common in nature. So, the composition of the earth's crust mainly includes silicas and silicates. These include feldspar, various clays, mica, talc and many others. Silicates are also included in the composition of rocks - granite, basalt and others. Silicate crystals are also such famous stones, which, due to their rarity and beauty, are considered precious, such as emeralds, topazes and aquamarines.
Most silicates are not soluble in water. The only exceptions are sodium and potassium silicates . They can be obtained by fusion with the corresponding hydroxide or carbonate. For example,
+ = +
Aqueous solutions of salts obtained in this way are called “water glass”. It is widely used as a binder in the production of acid-resistant concrete, and in addition, it is used in the manufacture of the well-known window putty and stationery glue. As a fire-resistant and waterproof impregnation, they also process products from fabric, wood and paper.
Silicates containing aluminum are called aluminosilicates. These include mica and feldspar, although their composition is much more complicated. So, feldspar, in addition to silicon oxide and aluminum oxide also contains oxides of sodium, potassium and sodium. In addition to aluminum and silicon, mica contains hydrogen, sodium or potassium, but can be, although less common, also calcium, magnesium or iron.
In general, the use of silicates in modern conditions is very wide and diverse. Silicate rocks are used as building materials. Silicates are used as raw materials in the production of cement, various fillers for ceramics, glass, etc. Mica and asbestos are used in the manufacture of various thermal and electrical insulating materials.