Oxoacids of Phosphorus preparation and properties, Group 15 P Block Elements

Oxoacids of Phosphorus preparation and properties, Group 15 P Block Elements

Oxoacids of Phosphorus :

→ Phosphorus forms various oxoacids. In these oxoacids two are very important :

  • Phosphorus acid
  • Phosphoric acid

→ Other oxo acids are formed by above two acids. The series formed by oxo acids contain a tetrahedral phosphorus atom which is co-ordinated to four atoms. The compositions of the oxo acids are inter-related in terms of loss or gain of H2O molecule or O atom. The rules related to draw the structure of oxo acids are as follows:

  • It must have at least one P = O linkage.
  • It must have at least one P – OH linkage.
  • It can have either P – H or P – P linkage but not both.
  • If a molecule has P – H linkage then it behave as a good reducing agent.

→ P – H bonds are not ionisable to give H+ and do not play any role in basicity. Only those H atoms which are attached with oxygen in POH form are ionisable and cause the basicity. If a molecule has one-OH bond then its basicity is one or if it has two-OH bond then it basicity is two.

→ The oxo acids in which phosphorus has lower oxidation state (less than +5) contain, P = O, P – OH bonds either with P – P or P – H bonds but not both.

Oxoacids of Phosphorus preparation and properties, Group 15 P Block Elements

→ Hypophosphorus acid is a good reducing agent as it contains two P-H bonds and reduces for example AgNO3 into metallic silver.
4AgNO3 + 2H2O + H3PO2 ? 4Ag + 4HNO3 + H3PO4

→ The acids having +3 oxidation state of phosphorus tends to disproportionate to higher and lower oxidation states. For example, orthophosphorus acid on heating disproportionates to give orthophosphoric acid and phosphine.

4H3PO3 — 3H3PO4 + PH3

Structure of Some oxo acids

Some important structure of oxo acids are as follows:

Oxoacids of Phosphorus preparation and properties, Group 15 P Block Elements 1
Oxoacids of Phosphorus preparation and properties, Group 15 P Block Elements 2
Oxoacids of Phosphorus preparation and properties, Group 15 P Block Elements 3

→ The important oxoacids of phosphorus with their formulae, methods of preparation and presence of some characteristic bonds in their structure are given in table 7.9:

Oxoacids of Phosphorus preparation and properties, Group 15 P Block Elements

Table 7.9: Oxoacids of Phosphorus

Oxoacids of Phosphorus preparation and properties, Group 15 P Block Elements 4

Chemistry Notes

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