Waterglass

Sodium silicate

Names
IUPAC name Sodium metasilicate
Other names Liquid glass Waterglass
Identifiers
CAS Number	6834-92-0 Y
3D model (Jmol)	Interactive image
Abbreviations	E550
ChEBI	CHEBI:60720 Y
ChemSpider	21758 Y
ECHA InfoCard	100.027.193
EC Number	229-912-9
MeSH	Sodium+metasilicate
PubChem	23266
RTECS number	VV9275000
UN number	3253
InChI InChI=1S/2Na.O3Si/c;;1-4(2)3/q2*+1;-2 Y Key: NTHWMYGWWRZVTN-UHFFFAOYSA-N Y InChI=1/2Na.O3Si/c;;1-4(2)3/q2*+1;-2 Key: NTHWMYGWWRZVTN-UHFFFAOYAB
SMILES [Na+].[Na+].[O-][Si]([O-])=O
Properties
Chemical formula	Na2SiO3
Appearance	White to greenish opaque crystals
Density	2.61 g/cm3
Melting point	1,088 °C (1,990 °F; 1,361 K)
Solubility in water	22.2 g/100 ml (25 °C) 160.6 g/100 ml (80 °C)
Solubility	insoluble in alcohol
Refractive index (nD)	1.52
Thermochemistry
Specific heat capacity (C)	111.8 J/(K·mol)
Std molar entropy (So298)	113.71 J/(K·mol)
Std enthalpy of formation (ΔfHo298)	−1561.43 kJ/mol
Gibbs free energy (ΔfG˚)	−1427 kJ/mol
Hazards
Safety data sheet	Avantor Performance Materials
EU classification (DSD)	C
R-phrases	R34, R37
S-phrases	(S1/2), S13, S24/25, S36/37/39, S45
NFPA 704	0 2 0
Lethal dose or concentration (LD, LC):
LD50 (median dose)	1153 (rat, oral)
Related compounds
Other anions	Sodium carbonate
Other cations	Potassium silicate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
Infobox references

Sodium silicate is the common name for compounds with the formula (Na₂SiO₂)_nO. A well-known member of this series is sodium metasilicate, Na₂SiO₃. Also known as waterglass or liquid glass, these materials are available in aqueous solution and in solid form. The pure compositions are colourless or white, but commercial samples are often greenish or blue owing to the presence of iron-containing impurities.

They are used in cements, passive fire protection, textile and lumber processing, refractories, and automobiles. Sodium carbonate and silicon dioxide react when molten to form sodium silicate and carbon dioxide:

Anhydrous sodium silicate contains a chain polymeric anion composed of corner-shared {SiO₄} tetrahedral, and not a discrete SiO₃²⁻ ion. In addition to the anhydrous form, there are hydrates with the formula Na₂SiO₃·nH₂O (where n = 5, 6, 8, 9), which contain the discrete, approximately tetrahedral anion SiO₂(OH)₂²⁻ with water of hydration. For example, the commercially available sodium silicate pentahydrate Na₂SiO₃·5H₂O is formulated as Na₂SiO₂(OH)₂·4H₂O, and the nonahydrate Na₂SiO₃·9H₂O is formulated as Na₂SiO₂(OH)₂·8H₂O.

In industry, the various grades of sodium silicate are characterized by their SiO₂:Na₂O weight ratio (weight ratios can be converted to molar ratios by multiplication with 1.032), which can vary between 2:1 and 3.75:1. Grades with this ratio below 2.85:1 are termed alkaline. Those with a higher SiO₂:Na₂O ratio are described as neutral.

Water glass was defined in Von Wagner's Manual of Chemical Technology (1892 translation) as any of the soluble alkaline silicates, first observed by Jean Baptist van Helmont around 1640 as a fluid substance made by melting sand with excess alkali.Glauber made what he termed "liquor silicum" in 1646 from potash and silica.Johann Nepomuk von Fuchs, in 1818, obtained what is now known as water glass by treating silicic acid with an alkali, the result being soluble in water, "but not affected by atmospheric changes". Von Wagner distinguished soda, potash, double (soda and potash), and fixing (i.e., stabilizing) as types of water glass. The fixing type was "a mixture of silica well saturated with potash water glass and a sodium silicate" used to stabilize inorganic water color pigments on cement work for outdoor signs and murals.