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Phosphorous acid is a colorless crystal. It can be slowly oxidized to phosphoric acid in the air. When heated to 180 °C, it can be decomposed into phosphoric acid and phosphine (highly toxic). As a dibasic acid, it has slightly be acidity than phosphoric acid. Phosphorous acid has b reducibility and can easily reduce Ag+ to metal silver. It can also reduce sulfuric acid to sulfur dioxide. It is corrosive and has hygroscopicity.
Relative Density: 1.651 (21.1 °C)
Melting Point: 73.6 °C
Boiling Point: 200 °C (Decomposes)
Solubility: Easily soluble in water and alcohol.
| Specification | A Grade | B Grade |
| Main Content(based on H3PO3 ) (%) | ≥ 99.0 | ≥ 98.5 |
| Iron Content(based on Fe) (%) | ≤ 0.001 | ≤ 0.003 |
| Chloride Content(based on CL) (%) | ≤ 0.01 | ≤ 0.02 |
| Sulfate Content(based on SO4) (%) | ≤ 0.008 | ≤ 0.01 |
| Phosphate Content(based on PO4) (%) | ≤ 0.2 | ≤ 0.6 |
| Appearance | Pure white crystal | White crystal |
| 70% Aqueous Solution Test | Colorless transparent | Colorless transparent, without impurities |
| Liquid Phosphorous Acid (%) | ≥ 70-80 | Colorless, transparent |
The application of phosphorous acid:
used in water treatment, as a food additive and in the production of fertilizers, make up Chemical fertilizers, detergents, food and feed additives, flame retardants and various phosphates.