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Phosphorous acid

Chemical formula of phosphorous acid: H3PO3


Phosphorous acid is a molecular compound, meaning that a covalent bond is established between its constituent atoms. In this structure, phosphorous is the central atom and two OH groups, one O atom and one H atom are attached to it. The phosphorous atom uses SP3 hybrid orbitals to give the molecule a four-dimensional structure. Due to the electronegative difference between oxygen and phosphorous, as well as oxygen and hydrogen, most of the bonds in this molecular are polar, leading to phosphorous acid being a polar molecule.

Physical properties

It is a polar molecule and dissolves well in solvents such as water. The attraction between phosphorous acid molecules is of the bipolar – dipolar force type, and also a hydrogen bond is formed between these molecules (between hydrogen attached to oxygen from one molecule and oxygen from another molecule).

How to prepare

The main method of preparing phosphorous acid is to dissolve P4O6 or tetraphosphorous hexoxide (diphosphorous trioxide) in water:

P4O6 + H2O → 4H3PO3

Chemical properties

The most important chemical property of phosphorous acid is its acidic nature. There are two hydrogen atoms in this molecule that are attached to the oxygen atom and are considered acidic hydrogen. phosphorous acid then acts as a dual proton acid in aqueous medium. It should be noted that in non-aqueous environments, hydrogen attached to phosphorous can also be acidic.

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