Class 12 Chemistry P Block Elements Formation of oxy-acids

Formation of oxy-acids

 

(a)Oxy-acids of nitrogen: nitrogen forms four types of oxy-acids that is:

  • Nitric acid (HNO3)
  • Nitrous acid (HNO2)
  • Hypo nitrous acid (H2N2O2)
  • Per nitric acid (HNO4).

 

Nitrous acid: Nitrous acid oxidizes H2S to S ,KI to I2 and act as an oxidizing agent. In the presence of strong oxidizing agent it also acts as reducing agent like it reduces potassium dichromate etc to form complex.

It structure is:

 Class_12_P_Block_Preparation_Of_Structure_Of_Nitrous_Oxide

Nitrous acid

 

Nitric acid:

  • It stains skin yellow due to formation of nitro compound xanthoprotein. It is also called as aqua Fortis meaning strong water because it attacks almost all metals.
  • It also forms a constant boiling mixture with water which has 68% of acid.
  • Concentrated nitric acid attains a yellow color on standing. This is due to the presence of nitrogen dioxide which is formed due to decomposition of nitric acid in sunlight. This yellow color may be removed by warming it or bubbling air through it.
  • Fuming nitric acid contains nitrogen dioxide in concentrated nitric acid. It is obtained by distilling concentrated nitric acid with little amount of starch.
  • It structure is:

 Class_12_P_Block_Preparation_Of_Structure_Of_Nitric_Acid

                            Nitric acid

Hypo nitrous acid:

  • It is a weak dibasic acid
  • Its structure is:

    Class_12_P_Block_Preparation_Of_Structure_Of_HypoNitrous_Acid

Hypo nitrous acid

Oxy-acids of phosphorous: Its oxy acids are:

  • Hypo phosphorous acid (H3PO2)
  • Phosphorous acid (H3PO3)
  • Orthophosphoric acid (H3PO4)
  • Metaphosphoric acid (HPO3)
  • Hypo phosphoric acid (H4P 2 O6)
  • Pyro phosphoric acid (H4P2 O7)
  • Pyro phosphorus acid (H4P2 O5)
  • Isohyphosphoric acid (H4P2 O6)

Their structures are given below:

 Class_12_P_Block_Preparation_Of_Structure_Of_Oxy-Acids_Of_Phosphorous

Hypo phosphoric acid

  • It is also called as phosphinic acid.
  • It is powerful reducing agent because of the presence of two P-H bonds.
  • The oxidation state of P is +1(monobasic).

Phosphorous acid

  • It is also called as phosphonic acid.
  • It is dibasic acid.
  • In it the oxidation state of P is +3.
  • It is strong reducing agent but weaker than hypo phosphorous acid due to only one P-H bond.
  • It undergoes disproportionate reaction giving orthophosphoric acid and phosphine.

Orthophosphoric acid

  • It is a weak tri basic acid.
  • In it the P is in +5 oxidation state.
  • It has no oxidizing or reducing properties.
  • On heating it gives pyro phosphoric acid at 525K and meta phosphoric at 875K.

           H3PO4àH4P2O7 àHPO3

                (At 525K)     (At 875K)

 Metaphosphoric acid

  • It is also called as glacial phosphoric acid.
  • It is monobasic having P in +5 oxidation state.
  • It has no reducing property.
  • It exists as polymer and thus contains P-O-P bonds which can further form calgon.

 Hypo phosphoric acid

  • It is tetra basic in nature.
  • Due to absence of P-H bond it has no reducing properties.
  • In the P is in +4 oxidation state.

Pyro phosphoric acid

  • It is also called as di phosphoric acid.
  • In it the oxidation state is +5.
  • It is also tetra basic.
  • It has no reducing property.

 

Pyrophosphorous acid

  • It is also called as di phosphorous acid.
  • In it the oxidation state of P is +3.
  • It contains P-O-P bond and is dibasic.
  • It is strong reducing agent due to presence of P-H bonds.

Isohyphosphoric acid

  • It contains one P-O-P bond and one P-H bond.
  • It is also called as diphosphoric acid.
  • It is tri basic in nature in it the oxidation state of P is +3 which are attached to hydrogen and rests have +5 oxidation state.
  • It has reducing properties also.

 

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