Silicate (from the Latin language the word "silex" is translated as "stone") refers to the salts of metacilic acid H2SiO3. For example, sodium silicate , the chemical formula of which is written as follows: Na2SiO3. Another name for the salt is sodium metasilicate. The molar mass of the substance is 122.06 g / mol. Appearance - white opaque crystals with a greenish tint. The density is 2.4 g / cm3. The degree of purity is characterized by a refractive index of 1.52. Melting point - plus 1088 ° C. The substance is soluble in water and insoluble in alcohol. The diluted aqueous solution has unique properties: fresh eggs immersed in it can be stored at room temperature for up to nine months. Sodium silicate is stable in a neutral and alkaline environment, and in an acidic 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 ordinary sand, which is formed due to the destruction of rocks. Under the action of alkali on silicon dioxide, a chemical reaction proceeds: NaOH + SiO2 → Na2SiO3 + H2O. The result is a salt of silicic acid - sodium silicate. Hydrolysis of salt (its decomposition with water) proceeds according to the scheme: 2Na2SiO3 + H2O → Na2SiO5 + 2NaOH, and sodium dimethasilicate is formed. With a decrease in the concentration of the solution, hydrolysis proceeds more intensively. In 1 N. the solution is hydrolyzed by 14% salt, in 0.1 N. - 28%, in 0.001% - 32%. The hydrolysis of sodium dimethasilicate is already weaker.
Sodium silicate is formed as a result of the interaction of silicon with alkali: Si + H2O + 2NaOH → Na2SiO3 + 2H2. A similar reaction can occur with weak alkalis, and also very easily goes with water in the presence of even a small amount of OH- anions: enough traces of alkalis extracted from glass. Since the sodium metasilicate formed is a salt of weak metasilicic acid, it is almost completely hydrolyzed in a dilute solution, the concentration of OH– ions during the reaction does not decrease, therefore, it all boils down to the decomposition of water by silicon. Alkali present is a catalyst. Of 0.63 kg of silicon in this way, 1 m3 of hydrogen is obtained, while iron would require almost 4 times more.
In industry, various grades of sodium silicate are characterized by a ratio 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 concentrated aqueous solutions is liquid or soluble glass. But along with Na2SiO3, other sodium silicates are also present in the liquid glass, therefore its usual composition is expressed by the formula, which is approximate, Na2O • nSiO2, where n = 2 ÷ 4. The gradual cleavage of SiO2 (usually during long-term storage) leads to cloudiness of the liquid glass or sometimes to a gelatinous mass. Therefore, in the laboratory it is kept in vessels closed with rubber stoppers, since the cortical or glass ones simply stick to the neck.
Sodium silicate is used in the manufacture of washing powders. The annual production of liquid glass is hundreds of thousands of tons. It is used to strengthen soils during construction work (for example, protecting concrete floor screed against abrasion), and also, like other reagents, for example, sodium tripolyphosphate, is used in many industries (both salts, for example, are used to soften water). Impregnation of Na2SiO3 concrete roads significantly reduces their abrasion.
Processing wood or other materials protects against fire (for example, buildings or theatrical scenery). Often serves as the basis for refractory putties or stationery glue. Putties that are simple in composition are suitable for gluing porcelain and glass. They can be obtained by mixing (up to the consistency of the test) chalk with liquid glass. The mixture quickly hardens and turns into a white and very durable mass.
From cement mixed with liquid glass, a quickly hardening putty is made, which is used to glue the stones. A mixture of sodium silicate with 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 burner due to strong smoke and an alarm.