Both phosphorous acid and phosphoric acid are inorganic acids, but they differ completely in appearance, physicochemical properties, production processes, prices, uses, and mechanisms of action. What are the differences and connections between phosphorous acid (H3PO3) and phosphoric acid (H3PO4)? We will compare and distinguish them from the following aspects, hoping to provide a reference for those working in the chemical industry.

1. The standards for H3PO3 and H3PO4 are different. The standard for H3PO3 is HG/T 2520-93. The standard for H3PO4 is GB/T 2091-2003 for industrial grade and GB 3149-2004 for food grade.

2. The phosphorus in H3PO3 is in the +valence valence, so it has reducing and antioxidant properties, and is a reducing agent. The phosphorus in phosphoric acid is in the +5valence valence, has neither reducing nor oxidizing properties, and is orthophosphoric acid.

3. The production processes and raw materials are completely different. The former is obtained by hydrolyzing PCl3 or treating dimethyl phosphite recovery solution to obtain crystals. The latter uses yellow phosphorus as the main raw material and is produced through thermal or wet processes.

4. The uses of phosphorous acid and phosphoric acid are completely different. Phosphorous acid is used as a reducing agent and has extensive applications in pesticide intermediates, nylon whitening, plastics, synthetic fibers, glyphosate production, water treatment agent ATMP, and organophosphorus pesticide production. Phosphoric acid (H3PO4) is mainly used in feed, flame retardants, electronics, and coatings industries.

5. The prices of the two are also completely different. Phosphoric acid is much more expensive than phosphoric acid, sometimes even twice as expensive. This is mainly due to the difference in their production costs.

6. H3PO3 is generally a white crystal with a content of about 98-99% and is a dibasic inorganic acid. Phosphoric acid, with the molecular formula H3PO4, has a content of about 75-85% and is a typical tribasic acid, generally a liquid.

Phosphorous acid and phosphoric acid are almost entirely different industries. As we can see from the above, their molecular structures, densities, standards, prices, mechanisms of action, uses, CAS numbers, TDS numbers, MSDS numbers, etc., are all completely different. Therefore, one cannot simply understand these chemicals from a literal perspective; a deep understanding from a chemical standpoint is essential.