Sodium metasilicate
{{Chembox
| Watchedfields = changed
| verifiedrevid = 476992453
| ImageFile1 = Na2SiO3idealized.png
| ImageClass1 = skin-invert-image
| ImageSize1 = 244
| ImageName1 = Structural formula of polymeric sodium silicate
| ImageFile2 = Sodium-metasilicate-chain-from-xtal-3D-balls.png
| ImageClass2 = bg-transparent
| ImageFile2_Ref = {{chemboximage|correct|??}}
| ImageSize2 = 244
| ImageName2 = Ball and stick model of polymeric sodium silicate
| ImageFile3 = Křemičitan sodný.PNG
| ImageFile3_Ref = {{chemboximage|correct|??}}
| ImageSize3 = 244
| ImageName3 = Sample of sodium silicate in a vial
| IUPACName = Sodium metasilicate
| OtherNames =
| Section1 = {{Chembox Identifiers
| index1_label = pentahydrate
| index2_label = nonahydrate
| Abbreviations = E550
| CASNo = 6834-92-0
| CASNo1 = 10213-79-3
| CASNo2 = 13517-24-3
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo2_Ref = {{cascite|correct|CAS}}
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 052612U92L
| UNII2_Ref = {{fdacite|correct|FDA}}
| UNII2 = D8D44215LZ
| PubChem = 23266
| PubChem1 = 61495
| PubChem2 = 61639
| ChemSpiderID = 21758
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| EINECS = 600-279-4
| EC_number = 229-912-9
| RTECS = VV9275000
| UNNumber = 1759 3253
| MeSHName = Sodium+metasilicate
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 60720
| SMILES = [Na+].[Na+].[O-][Si]([O-])=O
| StdInChI = 1S/2Na.O3Si/c;;1-4(2)3/q2*+1;-2
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| InChI = 1/2Na.O3Si/c;;1-4(2)3/q2*+1;-2
| StdInChIKey = NTHWMYGWWRZVTN-UHFFFAOYSA-N
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| InChIKey = NTHWMYGWWRZVTN-UHFFFAOYAB
}}
| Section2 = {{Chembox Properties
| Na=2 | O=3 | Si=1
| Formula = Na2SiO3
| Appearance = White crystals
| Density = 2.61 g/cm3
| MeltingPtC = 1088
| RefractIndex = 1.52
| Solubility = 22.2 g/100 ml (25 °C)
160.6 g/100 ml (80 °C)
| SolubleOther = insoluble in alcohol
}}
| Section3 = {{Chembox Thermochemistry
| DeltaHf = −1561.43 kJ/mol
| DeltaGf = −1427 kJ/mol
| Entropy = 113.71 J/(K·mol)
| HeatCapacity = 111.8 J/(K·mol)
}}
| Section4 = {{Chembox Hazards
| ExternalSDS = [http://www.avantormaterials.com/documents/MSDS/USA/English/S4982_msds_us_Default.pdf Avantor Performance Materials]
| NFPA-H = 2
| NFPA-F = 0
| NFPA-R = 0
| LD50 = 1153{{clarify|reason=units?|date=January 2017}} (rat, oral)
| GHSPictograms = {{GHS05}}{{GHS07}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|302|314|315|319|335}}
| PPhrases = {{P-phrases|260|261|264|270|271|280|301+312|301+330+331|302+352|303+361+353|304+340|305+351+338|310|312|321|330|332+313|337+313|362|363|403+233|405|501}}
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Sodium metasilicate is the chemical substance with formula {{chem|Na|2|SiO|3}}, which is the main component of commercial sodium silicate solutions. It is an ionic compound consisting of sodium cations {{chem|Na|+}} and the polymeric metasilicate anions [–{{chem|Si|O|3|2-}}–]n. It is a colorless crystalline hygroscopic and deliquescent solid, soluble in water (giving an alkaline solution) but not in alcohols.Chemical Book: [http://www.chemicalbook.com/ChemicalProductProperty_EN_CB2199386.htm "Sodium metasilicate"]. Accessed on 2018-05-13.
Preparation and properties
The anhydrous compound can be prepared by fusing silicon dioxide {{chem|SiO|2}} (silica, quartz) with sodium oxide {{chem|Na|2|O}} in 1:1 molar ratio.J. F. Schairer and N. L. Bowen (1956): "The system {{chem|Na|2|O}}—{{chem|Al|2|O|3}}—{{chem|SiO|2}}". American Journal of Science, volume 254, issue 3, pages 129-195 {{doi|10.2475/ajs.254.3.129}}
The compound crystallizes from solution as various hydrates, such as
- pentahydrate {{chem|Na|2|SiO|3}}·5{{chem|H|2|O}} (CAS 10213-79-3, EC 229-912-9, PubChem 57652358)
- nonahydrate {{chem|Na|2|SiO|3}}·9{{chem|H|2|O}} (CAS 13517-24-3, EC 229-912-9, PubChem 57654617)M. F. Bechtold (1955): "Polymerization and Properties of Dilute Aqueous Silicic Acid from Cation Exchange" Journal of Physical Chemistry, volume 59, issue 6, pages 532–541. {{doi|10.1021/j150528a013}}
Structure
In the anhydrous solid, the metasilicate anion is actually polymeric, consisting of corner-shared {SiO4} tetrahedra, and not a discrete SiO32− ion.{{Greenwood&Earnshaw}}
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.Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications {{ISBN|0-19-855370-6}} The pentahydrate and nonahydrate forms have their own CAS Numbers, [https://pubchem.ncbi.nlm.nih.gov/compound/Sodium_metasilicate_pentahydrate 10213-79-3] and [https://pubchem.ncbi.nlm.nih.gov/compound/Sodium_metasilicate_nonahydrate 13517-24-3] respectively.
Uses
Sodium Metasilicate reacts with acids to produce silica gel.{{cite web|url=https://sciencing.com/uses-sodium-metasilicate-5447484.html|title = Uses of Sodium Metasilicate| date=24 April 2017 }}
- Cements and Binders - dehydrated sodium metasilicate forms cement or binding agent.
- Pulp and Par - sizing agent and buffer/stabilizing agent when mixed with hydrogen peroxide.
- Soaps and Detergents - as an emulsifying and suspension agent.
- Automotive applications - decommissioning of old engines (CARS program), cooling system sealant, exhaust repair.
- Egg Preservative - seals eggs increasing shelf life.
- Crafts - forms "stalagmites" by reacting with and precipitating metal ions. Also used as a glue called "soluble glass".
- Hair coloring kits