Sodium silicate

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Sodium silicate
Sodium silicate.png
Names
IUPAC name
Sodium metasilicate
Other names
Liquid glass
Sodium polysilicate
Sodium siliconate
Waterglass
Properties
Na2SiO3
Molar mass 122.062 g/mol
Appearance White to greenish opaque crystals
Density 2.61 g/cm3
Melting point 1,088 °C (1,990 °F; 1,361 K)
Boiling point Decomposes
22.2 g/100 ml (25 °C)
160.6 g/100 ml (80 °C)
Solubility Insoluble in organic solvents
Vapor pressure ~0 mmHg
Thermochemistry
113.71 J·K-1·mol-1
−1561.43 kJ/mol
Hazards
Safety data sheet Sigma-Aldrich
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
1,153 mg/kg (rat, oral)
Related compounds
Related compounds
Sodium hydroxide
Silicon dioxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Sodium silicate, commonly known as water glass, is an ionic silicate of sodium. There are many compounds with the name "sodium silicate," but the most common is sodium metasilicate, Na2SiO3.

Properties

Chemical

Sodium silicate dissolves easily in water, forming a basic solution. It tends to form high hydrates, such as the pentahydrate and nonahydrate. Most metal salt solutions yield metal silicates upon treatment with sodium silicate, some similar in composition to silicate minerals. Sodium silicate can also act as a flocculating agent or to increase the viscosity of a liquid mixture, as well as a component in some cements.

Sodium silicate has the interesting property to decompose when treated with organic solvents such as ethanol and acetone. This results in formation of a resilient rubber-like gel, which is a form of silica gel. If this gel is dried and calcinated, very fine powders of SiO2 can be made. You can also sculpt small balls from this gel, which will solidify into hard marbles. Boiling chips can be made this way, since fully dried silica gel is very porous, which makes it prime boiling chip material.

Physical

Sodium silicate forms glassy, colorless crystals. It is slightly soluble in cold water (22.2 g/100 ml at 25°C), but more so in hot water. It is insoluble in alcohol.

Availability

Sodium silicate can be found at some chemical supply stores, though it may be easier to make it. In some countries, a concentrated solution of waterglass is sold very cheaply as an office glue. Waterglass can also be found in hardware stores as a cement mixing ingredient.

It is most of the time sold as solution.

Preparation

Sodium silicate can prepared by heating a sodium hydroxide solution with silica gel. A more dangerous method of preparation is to add plain glass scrap (not lead oxide glass or borosilicate glass) to molten sodium hydroxide. Rather than using glass, cleaned silica sand can be added instead. After thorough mixing of the silica into the sodium hydroxide(an excess of the silica is required to prevent sodium hydroxide in the product), the mass of reactants hardens, and can be leached with warm water to obtain a viscous solution of sodium silicate.

Projects

Handling

Safety

Sodium silicate is not particularly toxic, though it may contain free alkali and gloves should be worn when handling the protection.

Storage

Solid sodium silicate can be stored in closed containers. Silicate solutions should be stored at temperatures lower than 60°C, as higher temperatures tend to promote dehydration of the silicate, causing a surface skin to be formed.[1]

Disposal

Sodium silicate can be neutralized with an acid and since the byproducts are not toxic, they can be safely disposed of.

References

  1. http://www.pqcorp.com/Portals/1/lit/bulletin_17-70.pdf

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