Sodium metasilicate
[CAS 6834-92-0]

Identification

• Classification: Inorganic chemical industry >> Inorganic salt >> Silicide and silicate
• Name: Sodium metasilicate
• Synonyms: Disodium metasilicate
• Molecular Formula: Na₂SiO₃
• Molecular Weight: 122.06
• CAS Registry Number: 6834-92-0
• EC Number: 229-912-9
• SMILES: [O-][Si](=O)[O-].[Na+].[Na+]

Properties

• Melting point: 1089 °C

Safety Data

• Hazard Symbols: GHS05;GHS07 Danger
• Risk Statements: H314-H335
• Safety Statements: P260-P261-P264-P271-P280-P301+P330+P331-P302+P361+P354-P304+P340-P305+P354+P338-P316-P319-P321-P363-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin corrosion	Skin Corr.	1B	H314
Specific target organ toxicity - single exposure	STOT SE	3	H335
Serious eye damage	Eye Dam.	1	H318
Substances or mixtures corrosive to metals	Met. Corr.	1	H290
Acute toxicity	Acute Tox.	4	H302
Chronic hazardous to the aquatic environment	Aquatic Chronic	3	H412
Specific target organ toxicity - single exposure	STOT SE	3	H370
Specific target organ toxicity - single exposure	STOT SE	3	H336
Skin corrosion	Skin Corr.	1A	H314

• Transport Information: UN 3253

chemBlink Chemical Story

Sodium metasilicate, CAS 6834-92-0, is an inorganic sodium silicate commonly represented by the formula Na₂SiO₃. It is a strongly alkaline, water-soluble solid used in detergents, cleaning formulations, ceramics, construction materials, and numerous industrial processes. Yet its most interesting chemistry begins when the apparently simple formula Na₂SiO₃ meets water. Silicate in solution does not behave as a collection of permanently fixed SiO₃²⁻ units. Its forms change with pH, concentration, and the surrounding chemical environment, and under suitable conditions soluble silicate can ultimately become a three-dimensional silica gel.

Silicon and carbon occupy the same group of the periodic table, but their chemistry developed in very different directions. Carbon readily forms stable chains through carbon-carbon bonds. Silicon has a particularly strong affinity for oxygen, and much of terrestrial silicon occurs in structures built from silicon surrounded by oxygen atoms. Silicate minerals make up an enormous fraction of Earth's crust, while silica occurs in materials ranging from quartz to amorphous silica.

Sodium silicates provide a way of bringing some of this silicon-oxygen chemistry into water. When sodium metasilicate dissolves, its strongly alkaline solution contains sodium ions together with protonated and deprotonated silicate species whose relative amounts depend on conditions. The alkalinity is important because high pH helps keep silicate species dispersed in solution.

This is one reason sodium metasilicate is useful in cleaning formulations. Its alkalinity helps neutralize acidic soils and assists the removal of fats and other organic deposits. Silicate species can also interact with surfaces and metal ions, and sodium silicates can contribute to detergency, buffering, dispersion, and corrosion control in appropriately designed formulations.

The same alkaline environment that makes sodium metasilicate useful as a cleaner also keeps its silicon chemistry from taking a very different path. Lower the pH and silicate species become increasingly protonated. Silanol groups, commonly represented as Si-OH, can then undergo condensation reactions with one another.

A simplified condensation can be written:

Si-OH + HO-Si → Si-O-Si + H₂O

The new Si-O-Si connection is called a siloxane bond. Repeating this process allows individual silicon-containing species to become linked into increasingly large structures. Small species become oligomers, larger particles or networks develop, and under suitable conditions a continuous three-dimensional silica-rich network can form throughout the liquid.

The result is a gel.

A gel is a particularly interesting state of matter because it can look and behave like a soft solid while still containing a large amount of liquid. In silica gel, a connected solid silica network extends through the material and traps liquid within its pores. The liquid has not simply frozen, and the material is not an ordinary crystalline solid. Its rigidity comes from a microscopic network that spans the sample.

This transition from soluble silicate to silica gel is one of the foundations of sol-gel chemistry. In a broader sol-gel process, molecular or colloidal precursors are transformed through hydrolysis and condensation into a connected inorganic network. By controlling composition, pH, concentration, temperature, aging, and drying, chemists can influence pore size, surface area, particle structure, and the properties of the final material.

Drying the gel introduces another transformation. Removing liquid from the pores leaves a porous silica-rich solid. Depending on how the gel is formed and dried, materials with very different pore structures can result. Silica gels are widely used as adsorbents and drying materials because their internal surfaces can interact strongly with water and other molecules.

The familiar packet marked "silica gel" is therefore chemically related to a much broader family of silicon-oxygen materials, although commercial desiccant silica gel should not simply be described as sodium metasilicate. Sodium silicate can serve as a starting source of soluble silicate, while acidification and condensation convert that soluble chemistry into a largely silica network.

This distinction is important. Na₂SiO₃ is a convenient formula for sodium metasilicate as a bulk substance, but the silica network produced after acidification is no longer simply Na₂SiO₃. Sodium ions and other soluble species can remain in or be removed from the system, while silicon atoms become connected through an extended Si-O-Si framework.

Sodium metasilicate also illustrates why sodium silicates are often associated with the older term "water glass." Certain sodium silicate compositions form viscous aqueous solutions that can act as binders and inorganic adhesives. As water is removed or silicate becomes polymerized, increasingly connected silicon-oxygen structures develop. This behavior has led to applications in cements, foundry binders, coatings, refractory materials, and other industrial products.

The chemistry also explains why sodium metasilicate must be handled with respect. Its aqueous solutions are strongly alkaline and can cause serious damage to skin and eyes. A material can be derived from the same silicon-oxygen chemistry found throughout rocks and minerals yet behave very differently when converted into a concentrated, soluble alkaline salt.

That contrast is part of what makes sodium metasilicate interesting. Silicon in a rock may be locked into an insoluble mineral structure for geological periods. Convert silicon-oxygen chemistry into an alkali-metal silicate and it can enter an aqueous industrial process. Change the pH, and those dissolved species can begin connecting to one another again, eventually producing an extended solid network.

A bottle of sodium metasilicate therefore contains more than an alkaline cleaning ingredient. It contains a soluble route into network-forming inorganic chemistry.

Add water and silicate enters solution. Change the acid-base environment and Si-O-Si bridges begin to form. Continue the process and a liquid can lose its ability to flow, not because it froze, but because a microscopic inorganic network has grown through it.

It is an elegant demonstration of a central idea in materials chemistry: sometimes the difference between a solution and a solid is simply whether enough atoms have learned how to connect.

References

1. Iler, R. K. (1979). The Chemistry of Silica: Solubility, Polymerization, Colloid and Surface Properties, and Biochemistry. Wiley.

2. Brinker, C. J.; Scherer, G. W. (1990). Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing. Academic Press.

3. PubChem. Sodium metasilicate, CAS 6834-92-0. Identity, physicochemical properties, uses, and safety information.

4. Published literature on aqueous silicate speciation, silica polymerization, and sodium silicate-based sol-gel processes.

5. Industrial literature on sodium silicates in detergents, cleaners, binders, coatings, and corrosion-control formulations.