Phosphorous Acid (H₃PO₃), also known as Phosphorus Acid, is a colorless to pale-yellow crystalline solid widely used as a reducing agent and chemical intermediate. It plays a key role in the production of phosphonate-based water treatment chemicals, agrochemicals, and specialty additives. In agriculture, it serves as a precursor for fungicidal formulations, while in industrial processing it supports scale and corrosion control applications. Valued for its high reactivity, purity, and versatility, Phosphorous Acid delivers reliable performance across chemical manufacturing, water treatment, and agricultural sectors.
| Property | Specification |
|---|---|
| Product Name | Phosphorous acid |
| CAS No | 13598-36-2 |
| Chemical Name/Synonyms | Phosphonic Acid; H3PO3; Orthophosphorous Acid |
| Chemical Formula | H₃PO₃ |
| Appearance (Color) | White to yellowish deliquescent crystals or liquid |
| Molecular Weight | 82.00 g/mol |
| HS Code | 2811.19 |
| TSCA Inventory | Active |
More identifiers
| |
| Property | Typical Classification |
|---|---|
| GHS Signal Word | Danger |
| GHS Pictograms | Corrosion (GHS05), Exclamation mark (GHS07) |
| UN Number | UN 2834 |
| Proper Shipping Name | Phosphorous acid |
| Transport Hazard Class | 8 |
| Packing Group | III |
| Flash Point | Not applicable |
Typical U.S. classification for this product: label elements under OSHA’s Hazard Communication Standard (29 CFR 1910.1200) and transport under U.S. DOT (49 CFR 172.101), compiled from manufacturers’ safety data sheets and harmonised GHS classifications, checked October 2026. Environmental hazards are shown for information; the OSHA label does not cover them. Classification can differ by supplier, grade and concentration: the supplier’s U.S.-format SDS, sent with your quote, is the governing document.
Provides precise pH control for chemical synthesis and water treatment.
Aggressively dissolves mineral deposits, scale, and rust from metal surfaces.
Acts as a foundational reagent and catalyst in various organic syntheses.
Conditions and etches metal surfaces prior to plating or coating.
Effectively neutralizes alkaline streams in effluent treatment plants.
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Before we recommend a manufacturer, we check it in five layers: its documents (COA, SDS, certifications), its business license and IEC status with India’s DGFT, its standing with our industry contacts, an in-person visit to the facility, and its export record.
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Our American-led team in India can be at a supplier’s site, check its machinery and real capacity, sit in on negotiations and review documents in person, then report back to you directly, with photos and video from the factory floor.
Going the other way? If you make a specialty chemical or industrial product and want to sell it in India, we provide the on-ground presence and industry network to open that market.
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Consistent quality and international standards.
Bulk availability with on-time delivery.
Flexible packaging options as per requirement.
Technical guidance and dedicated customer support.
