Silicotungstic acid hydrate
[CAS 12027-43-9]

Identification

• Classification: Inorganic chemical industry >> Inorganic acid
• Name: Silicotungstic acid hydrate
• Synonyms: Tungsten hydroxide oxide silicate hydrate
• Molecular Formula: H₄[Si(W₃O₁₀)₄] .xH₂O
• CAS Registry Number: 12027-43-9
• EC Number: 681-167-2
• SMILES: O.O[Si](O)(O)O.O=[W]1(=O)O[W](=O)(=O)O[W](=O)(=O)O1.O=[W]2(=O)O[W](=O)(=O)O[W](=O)(=O)O2.O=[W]3(=O)O[W](=O)(=O)O[W](=O)(=O)O3.O=[W]4(=O)O[W](=O)(=O)O[W](=O)(=O)O4

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H315-H319-H335
• Safety Statements: P261-P264-P264+P265-P271-P280-P302+P352-P304+P340-P305+P351+P338-P319-P321-P332+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin irritation	Skin Irrit.	2	H315
Eye irritation	Eye Irrit.	2	H319
Specific target organ toxicity - single exposure	STOT SE	3	H335
Skin corrosion	Skin Corr.	1C	H314
Substances or mixtures corrosive to metals	Met. Corr.	1	H290
Serious eye damage	Eye Dam.	1	H318

chemBlink Chemical Story

Silicotungstic acid belongs to the polyoxometalates, a family in which many metal-oxygen units assemble into large, discrete inorganic clusters. Its well-known Keggin architecture places a central silicate unit inside a framework built from twelve tungsten-oxygen octahedra.

The cluster is strongly acidic and can also participate in redox chemistry. This combination explains its use as a catalyst in esterification, oxidation, and related reactions. Unlike a simple mineral acid, a heteropolyacid can sometimes be supported on solids or incorporated into hybrid materials, which may simplify catalyst recovery.

Its story is that the line between molecule and material is not always sharp. Silicotungstic acid is much larger than a conventional acid molecule, yet far more structurally defined than an amorphous oxide surface. Inorganic chemistry can therefore build nanoscale catalytic function from repeating metal-oxygen units.

References:
Sigma-Aldrich. Tungstosilicic acid hydrate, CAS 12027-43-9.
Polyoxometalate reviews on Keggin heteropolyacids and catalysis.

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