Silicic acid and its use
Silicic acid theoretically representsa compound of silicon oxide and water. And the ratio of these components can be very diverse. Therefore, in the general form, 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 transfer from one state to another. Thus, n and m in this case can be considered as variable values.
Theoretically, silicic acid can bewas obtained by the interaction of a silicate of one of the alkali metals (for example, sodium) and one of the "strong" acids (eg, hydrochloric acid). In this way, some of these acids were isolated in the free state: metasilicic, orthosilicic, and others. For example, the chemical reaction for the preparation of metasilicic acid:
+ 2HCl = + 2NaCl
However, to prepare in pure form silicic acidalmost impossible. In aqueous solutions (and they get supersaturated), silicic acid as a result of the polymerization process becomes the basis for the formation of colloidal solutions that have a fairly short period of existence. Further from these solutions, as a result of coagulation, a gel is formed. This is the application of silicic acid, since by drying this gel, a so-called silica gel is obtained, which is used as a desiccant and absorbent. In addition, using special stabilizers, colloidal solutions produce persistent colloids (or sols), which also find application in production.
Silicic acid is slightly soluble, weak and thermally unstable. When heated, the decomposition of silicic acid takes place, which is expressed by the following chemical reaction:
=
It is also a weaker acid than the same coal. Because of 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:
= +
Salts of silicic acids are calledsilicates. They are very common in nature. Thus, the composition of the earth's crust is mainly composed of silica and silicates. These include feldspar, various clays, mica, talc and many others. Silicates also enter the rock formations - granite, basalt and others. Crystals of silicates are also such famous stones, which because of their rarity and beauty are considered precious, like emeralds, topazes and aquamarines.
Most silicates do not dissolve in water. Exceptions are only silicates of sodium and potassium. They can be obtained by melting with the appropriate hydroxide or carbonate. For example,
+ = +
Aqueous solutions in this way produced by salts,have the name "liquid glass". It is widely used as a binder in the production of acid-resistant concrete, and in addition, are used in the manufacture of all known window putty and clerical glue. As a fireproof and waterproof impregnation, they also handle products made of fabric, wood and paper.
Silicates, which contain aluminum,received the name aluminosilicates. These include mica and feldspar, although their composition is much more complicated. Thus, feldspar, in addition to silica and alumina, also contains oxides of sodium, potassium and sodium. In the mica, in addition to aluminum and silicon, there is hydrogen, sodium or potassium, but there may be, although less common, also calcium, magnesium or iron.
In general, the use of silicates in modernconditions is very wide and varied. Mountain silicate rocks are used as building materials. Silicates are used as raw materials in the production of cement, various fillers of ceramics, glass, etc. Mica and asbestos are used in the manufacture of various thermo- and electrical insulating materials.
