Question

Oxyacids of phosphorus and the starting material for their preparation are given below.

\[Oxyacids\]	\[Material{\text{ }}for{\text{ }}preparation\]
\[A.{\text{ }}{H_3}P{O_2}\]	\[\left( i \right){\text{ }}Red{\text{ }}P{\text{ }} + {\text{ }}alkali\]
\[B.{\text{ }}{H_3}P{O_3}\]	\[\left( {ii} \right){\text{ }}{P_4}{O_{10}} + {\text{ }}{H_2}O\]
\[C.{\text{ }}{H_3}P{O_4}\]	\[\left( {iii} \right){\text{ }}{P_2}{O_3} + {\text{ }}{H_2}O\]
\[D.{\text{ }}{H_4}{P_2}{O_6}\]	\[\left( {iv} \right){\text{ }}White{\text{ }}P{\text{ }} + {\text{ }}alkali\]

Choose the correct answer from the quotes given;
\[\left( A \right){\text{ }}A - \left( {iv} \right);{\text{ }}B - \left( {iii} \right);{\text{ }}C - \left( ii \right);{\text{ }}D - \left( {i} \right)\]
\[\left( B \right){\text{ }}A - \left( i \right);{\text{ }}B - \left( {iii} \right);{\text{ }}C - \left( {ii} \right);{\text{ }}D - \left( {iv} \right)\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\]
\[\left( C \right){\text{ }}A - \left( {iv} \right);{\text{ }}B - \left( {iii} \right);{\text{ }}C - \left( i \right);{\text{ }}D - \left( {ii} \right)\]
\[\left( D \right){\text{ }}A - \left( {ii} \right);{\text{ }}B - \left( {iii} \right);{\text{ }}C - \left( i \right);{\text{ }}D - \left( {iv} \right)\]

Answer 1

Hint: The oxoacids are those acids which contain oxygen. Phosphorous is known to form oxyacids such as, \[{H_3}P{O_4}\] ,\[{H_3}P{O_3}\],\[{H_3}P{O_2}\] , etc. The phosphorus in oxoacid is tetrahedral surrounded by atoms. Mostly, these all acids are having at least one \[P = O\] and one \[P - OH\] bond. An oxoacid, oxyacid or ternary acid is an acid that has oxygen.

Complete step-by-step answer:
These acids are found to be disproportionate to either lower or higher oxidation states. For example, when phosphorous acid is heated, it produces phosphine and phosphoric acid.
\[4{H_3}P{O_3}\, \to \,3{H_3}P{O_4}\, + \,P{H_3}\]

Phosphorous acid, \[{H_3}P{O_3}\]: \[{H_3}P{O_3}\] is a diprotic acid. It ionizes two protons. It is described with the structural formula \[HPO{\left( {OH} \right)_2}\] . When the hydrolysis occurs with phosphorus trichloride in the presence of acid or steam it forms \[{H_3}P{O_3}\] .
\[PC{l_3}\; + \;3\;{H_2}O\; \to \;HPO{(OH)_2}\; + \;3\;HCl\]
\[{P_2}{O_3}\,{\text{ + }}\,3{H_2}O\, \to \,\,2{H_3}P{O_3}\,(\,Phosphorus\,acid)\]

Phosphoric acid, \[{H_3}P{O_4}\]: \[{H_3}P{O_4}\] is a triprotic acid. It ionizes three protons. It is also non-toxic acid when it is pure, solid at room temperature and pressure. When sulphuric acid is added to tricalcium phosphate rock it forms phosphoric acid.
\[C{a_5}{(P{O_4})_3}X\; + \;5\;{H_2}S{O_4}\; + \;10\;{H_2}O\; \to \;3{H_3}P{O_4}\; + \;5\;CaS{O_4}.2{H_2}O\; + \;HX\]
\[X = \,F,\,Cl,\,Br\,and\,OH\]
\[{P_4}{O_{10}}\, + \,\,6{H_2}O\,\, \to \,\,{H_4}P{O_4}\,(phosphoric\,acid)\]

Hypophosphorous acid, \[{H_3}P{O_2}\]: \[{H_3}P{O_2}\] is produced when white phosphorous treated with alkali solution to produce \[{H_3}P{O_2}\].
\[{\text{White}}\,{\text{P}}\,{\text{ + }}\,{\text{Alkali}}\,{\text{produces}}\,\,{H_3}P{O_2}\]

Hypophosphoric acid, \[{H_4}{P_2}{O_6}\]: \[{H_4}{P_2}{O_6}\] is an acid of tetrabasic. It is formed by conduction of the controlled oxidation of red phosphorus with sodium chlorite. When the disodium salt is formed it gives hypophosphoric acid \[{H_4}{P_2}{O_6}\] via cation exchanger.
\[2P{\text{ }} + {\text{ }}2NaCl{O_2}\; + {\text{ }}2{H_2}O{\text{ }} \to {\text{ }}N{a_2}{H_2}{P_2}{O_6}\; + {\text{ }}2HCl\]
\[N{a_2}{H_2}{P_2}{O_6}\; + {\text{ }}2H\,\, \to \,resin\,\, \to {\text{ }}{H_4}{P_2}{O_6}\; + {\text{ }}2Na{\text{ }}-{\text{ }}resin\]

Therefore, the answer is,
\[{\text{White}}\,{\text{P}}\,{\text{ + }}\,{\text{Alkali}}\,{\text{produces}}\,\,{H_3}P{O_2}\]
\[{P_2}{O_3}\,{\text{ + }}\,3{H_2}O\, \to \,\,2{H_3}P{O_3}\,(\,Phosphorus\,acid)\]
\[{P_4}{O_{10}}\, + \,6{H_2}O\, \to \,{H_4}P{O_4}(phosphoric\,acid)\]
\[{\text{Red}}\,{\text{P}}\,{\text{ + }}\,{\text{Alkali}}\,{\text{produces}}\,\,{H_4}{P_2}{O_6}\]

So, the correct option is ‘A’.

Note: MetaPhosphoric, \[(HP{O_3})n\]: when orthophosphoric acid is warmed around \[860{\text{ }}K\]
the formation of meta phosphoric acid takes place. These exist in cyclic trimers, etc.
\[{H_3}P{O_4}\; \to {\text{ }}HP{O_3}\; + {\text{ }}{H_2}O\]
There are more oxoacids, oxyacids.