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Question: Which of the following contain \(P - P\) bond? (A) \[{P_2}O_7^{4 - }\] (B) \[{P_2}O_6^{3 - }\] ...

Which of the following contain P−PP - P bond?
(A) P2O74−{P_2}O_7^{4 - }
(B) P2O63−{P_2}O_6^{3 - }
(C) P2O93−{P_2}O_9^{3 - }
(D) P2O64−{P_2}O_6^{4 - }

Explanation

Solution

P-P bond means two phosphorus atoms are joined with each other and form a bridge between the molecules. P-P bond is a covalent bond, formed by the sharing of electrons by different atoms present in a molecule.

Complete step by step answer:
The prefix 'hypo-' means beneath or less than. Hypophosphoric acid has an oxidation state as +4 + 4 that is in between phosphoric acid and phosphorus acid. Thus, "hypophosphoric" refers to less than phosphoric but above the phosphorous acid.
Among the given options, hypophosphoric acid i.e. H4P2O64−{H_4}{P_2}O_6^{4 - } is a mineral acid. It has a +4 + 4 oxidation state. The two phosphorus atoms of the molecule form a covalent P-P bond as shown in the figure.

The structure of hypophosphorous acid is containing two P-O bonds with 151 pm151{\text{ }}pm length, P−OHP - OH bond with 151 pm151{\text{ }}pm length and P-P bond of 219 pm219{\text{ }}pm length. Hypophosphoric acid also has oxonium ions with formula [H3O+]2[H2P2O6]2−{[{H_3}{O^ + }]_2}{[{H_2}{P_2}{O_6}]^{2 - }} . The hypophosphoric acid is isostructural with the diammonium salt which containing [HOPO2PO2OH]2−{[HOP{O_2}P{O_2}OH]^{2 - }} anion with a P−P bond length of 219 pm.219{\text{ }}pm.
Dihydrate H4O2P6.2H2O{H_4}{O_2}{P_6}.2{H_2}O is the solid state of hypophosphoric acid, formed by the reaction of red phosphorus and sodium chlorite at room temperature.
2P+2NaClO2+2H2O→Na2H2P2O6+2HCl2P + 2NaCl{O_2} + 2{H_2}O \to N{a_2}{H_2}{P_2}{O_6} + 2HCl
Hence, the correct option is (A) P2O74−{P_2}O_7^{4 - }.

Additional information:
Hypophosphoric acid is used as a bleaching agent, reducing agent, stimulant in pharmaceutical agents and as a wetting agent. Hypophosphoric acid is triprotic and have dissociation constants pKa1  = 2.2, pKa2  = 2.8, pKa3  = 7.3 and pKa4  = 10.0p{K_{a1}}\; = {\text{ }}2.2,{\text{ }}p{K_{a2}}\; = {\text{ }}2.8,{\text{ }}p{K_{a3}}\; = {\text{ }}7.3{\text{ }}and{\text{ }}p{K_{a4}}\; = {\text{ }}10.0.

Note:
In air the hypophosphites oxidise and form pyrophosphates containing the P2O74−{P_2}O_7^{4 - } ion where P has an oxidation state of +5 + 5. They are stable to alkali hydroxides. It converts to the orthophosphate when fused with sodium hydroxide.