Question

What is the name of ${H_3}P{O_3}$ ?

Answer 1

Hint:
Phosphorus forms oxyacids with oxygen. All these compounds contain phosphorus atoms linked tetrahedrally to four other atoms or groups. Each of them has at least one $P \to O$ unit and one $P - OH$ group.

Complete step by step answer:
-Phosphorus forms a number of oxyacids. Each of them has at least one $P \to O$ unit and one $P - OH$ group. The $ - OH$ group is ionisable but hydrogen directly linked to phosphorus is not ionisable. Thus the number of $ - OH$ group decides the basicity of oxyacids.
-The given compound is also an oxyacid of phosphorus. It is called phosphorus acid. The phosphorus atom in this compound is $s{p^3}$ hybridized. The structure of phosphorus acid can be represented as follows-

-The two hydrogens are ionisable. The oxidation state of phosphorus atoms is $ + 3$. It is also called phosphonic acid.
-It is prepared by dissolving phosphorus trioxide in water.
${P_4}{O_6} + 6{H_2}O \to 4{H_3}P{O_3}$
-It can also be obtained by hydrolysis of phosphorus trichloride.
$PC{l_3} + 3{H_2}O \to {H_3}P{O_3} + 3HCl$
It is a crystalline colorless compound. It is highly soluble in water.
-When phosphorus acid is heated, it disproportionates into phosphoric acid and phosphine.
$4{H_3}P{O_3}\xrightarrow{{{{200}^\circ }C}}3{H_3}P{O_4} + P{H_3}$
It acts as a strong reducing agent. It reduces $CuS{O_4}$ to $Cu$, $AgN{O_3}$ to $Ag$, ${I_2}$ to $HI$.
$CuS{O_4} + 2H \to Cu + {H_2}S{O_4}$
$AgN{O_3} + H \to HN{O_3} + Ag$
${I_2} + 2H \to 2HI$
So the name of ${H_3}P{O_3}$ is phosphorus acid or phosphonic acid.

Additional information:
 Some other oxyacids of phosphorus are-
${H_3}P{O_2}$ - Hypophosphorous acid
${H_3}P{O_4}$ - Orthophosphoric acid
$HP{O_3}$ - Metaphosphoric acid
${H_4}{P_2}{O_6}$ - Hypophosphoric acid
${H_4}{P_2}{O_7}$ - Pyrophosphoric acid

Note: The hydrogen directly attached to phosphorus in ${H_3}P{O_3}$ is not ionisable. It is a diprotic oxyacid of phosphorus. It is used as a starting material for the synthesis of many phosphorus compounds. It is used as a strong reducing agent.