Sodium silicate

Silicates (from the Latin language the word "silex" is translated as "stone") are the salts of metasilicic acid H2SiO3. For example, sodium silicate, the chemical formula of which is written as follows: Na2SiO3. Another name for salt is sodium metasilicate. The molar mass of the substance is 122.06 g / mol. Appearance - white opaque crystals, which have a greenish tinge. The density is 2.4 g / cm3. The degree of purity is characterized by a refractive index, which is 1.52. The melting point is plus 1088 ° C. The substance is soluble in water and insoluble in alcohol. A dilute aqueous solution has unique properties: immersed in fresh eggs can be stored for up to nine months at room temperature. Sodium silicate is stable in a neutral and alkaline medium, and in the acid anion SiO3- reacts with H + cations to form silicic acid.

Silicon dioxide (also called silicon anhydride or silica) is the most stable compound that occurs in nature in the form of quartz. It accounts for 12% of the mass of the entire earth's crust. Quartz, contaminated with impurities, is a common sand, which is formed due to the destruction of rocks. Under the action of alkali on silicon dioxide, a chemical reaction takes place: NaOH + SiO2 → Na2SiO3 + H2O. As a result, a salt of silicic acid - sodium silicate is formed. Hydrolysis of the salt (decomposition by water) proceeds according to the scheme: 2Na2SiO3 + H2O → Na2SiO5 + 2NaOH, and sodium metasilicate is formed. With a decrease in the concentration of the solution, hydrolysis proceeds more intensively. In 1 n. 14% of the salt is hydrolyzed, 0.1N. - 28%, in 0,001% - 32%. The hydrolysis of sodium bimetasilicate proceeds more slowly.

Sodium silicate is formed as a result of the interaction of silicon with alkali: Si + H2O + 2NaOH → Na2SiO3 + 2H2. Such a reaction can proceed with weak alkalis, and also very easily proceeds with water in the presence of even a small amount of OH- anions: enough trace of alkalis extracted from the glass. Since the resulting sodium metasilicate is a salt of a weak metasilicic acid, in a dilute solution it almost completely hydrolyses, the concentration of OH-ions during the reaction does not decrease, so everything boils down to the decomposition of silicon by water. The presence of alkali is a catalyst. Of 0.63 kg of silicon in this way, 1 m3 of hydrogen is produced, whereas iron would have been almost 4 times more.

In industry, various grades of sodium silicate are characterized by a ratio of the amount of SiO2 and Na2O. It can vary from 2: 1 to 3.75: 1. Varieties with a ratio of 2.85: 1 and below are considered alkaline. Those with a higher ratio are characterized as "neutral". Sodium silicate in the form of aqueous concentrated solutions are liquid or soluble glass. But along with Na2SiO3, other sodium silicates are present in the liquid glass, so its usual composition is expressed by the formula, which is approximate, Na2O • nSiO2, where n = 2 ÷ 4. The gradual elimination of SiO2 (usually with prolonged storage) leads to turbidity of the liquid glass or to the transformation sometimes into a gelatinous mass. Therefore, in the laboratory, it is kept in containers closed with rubber stoppers, since cortical or glass bottles are simply glued to the neck.

Sodium silicate is used in the production of detergent powders. The annual production of liquid glass is hundreds of thousands of tons. It is used to strengthen the soil during construction work (for example, protection of the concrete floor screed against abrasion), and, like other reagents, for example sodium tripolyphosphate, is used in many industries (both salts, for example, are used for water softening). Impregnation of Na2SiO3 road concrete roads significantly reduces their attrition.

The processing of wood or other materials protects from fire (for example, buildings or theatrical scenery). Often serves as the basis for refractory putty or clerical glue. Simple in composition putty suitable for gluing porcelain and glass. They can be obtained by mixing (before the consistency of the dough) chalk with liquid glass. The mixture quickly solidifies and turns into a white and very strong mass.

From cement, mixed with liquid glass, make fast hardening putty, which is used for gluing stones. A mixture of sodium silicate and sawdust is used to fill the space between the double walls of some safes. This makes them more fire-resistant, and also serves as additional protection against opening with an acetylene torch due to a strong smoke and alarm.