Question

What is the IUPAC name for \[{H_3}P{O_3}\]?

Answer 1

Hint: IUPAC stands for International Union of Pure and Applied Chemistry. It is the world authority on the chemical nomenclature as well as terminology. In this question we have to tell the IUPAC name of\[{H_3}P{O_3}\] which is an oxyacid of phosphorus. It is a diprotic acid which readily ionizes two protons.

Complete step by step answer:
IUPAC provides consistency to the names of organic compounds. It enables every compound to possess a unique name, which otherwise is not plausible with the common names. The chemical structure for \[{H_3}P{O_3}\]is shown below:

\[{H_3}P{O_3}\]can be more clearly explained with its structural formula\[HPO{\left( {OH} \right)_2}\]. In solid state, \[HP\left( O \right){\left( {OH} \right)_2}\;\]is actually tetrahedral with\[P-H\] bond of\[1.32\;pm\], one short \[P = O\] bond of\[148\;pm\;\]while two long \[P-O\left( H \right)\]bonds of\[154\;pm\]. It occurs in equilibrium with a minor tautomer i.e. \[P{\left( {OH} \right)_3}\]. According to IUPAC nomenclature,\[{H_3}P{O_3}\]is called phosphorous acid, while the dihydroxy form is known as phosphonic acid. The reduced phosphorus compounds are only named with an ending "ous".
Hence, the IUPAC name for\[{H_3}P{O_3}\]is phosphorous acid.

Additional information:
Phosphorous acid (\[{H_3}P{O_3}\]), also known as orthophosphorous acid, is generally employed as a reducing agent in the chemical analysis. It is actually either a colourless or a yellowish crystalline substance having a melting point of around\[73^\circ C\], or\[163^\circ F\] and a taste similar to garlic. It is considered as an unstable compound which readily absorbs moisture, and gets converted to the phosphoric acid (\[{H_3}P{O_4}\]) in the presence of oxygen usually when heated above \[180{\text{ }}^\circ C\] (i.e.\[360{\text{ }}^\circ F\]). Phosphorous acid (\[{H_3}P{O_3}\]) generally leads to the formation of salts called as phosphites, which are employed as reducing agents.

Note: \[{H_3}P{O_3}\] is generally prepared by dissolving either tetraphosphorus hexoxide (\[{P_4}{O_6}\]) or phosphorus trichloride (\[PC{l_3}\]) in water. The reactions are demonstrated below:
$
  {P_4}{O_6} + 6{H_2}O \to 4{H_3}P{O_3} \\
  PC{l_3} + 3{H_2}O \to 3HCl + {H_3}P{O_3} \\
$