Phosphorous and Compounds

PHOSPHOROUS AND COMPOUNDS

Phosphorus

a)It shows the property of catenation to maximum extent due to most stable P – P bond.

b)It has many allotropes, the important ones are:
i)White phosphorus
ii)Red phosphorus
iii)Black phosphorus

White phosphorus

1. Discrete tetrahedral P4 molecules

2. Very reactive

3. Glows in dark

4. Translucent waxy solid

5. Soluble in but insoluble in water

6. It has low ignition temperature, therefore, kept under water

Red phosphorus

1. Polymeric structure consisting of chains of P4 units linked together

2. Less reactive than white phosphorus

3. Does not glow in dark

4. Has an iron grey lustre

5. Insoluble in water as well as

Black phosphorus

1. Exists in two forms – black phosphorus and black phosphorus

2. Very less reactive

3. Has an opaque monoclinic or rhombohedral crystals

Phosphine

1. It is highly poisonous, colourless gas and has a smell of rotten fish.

2. Preparation

Phosphorus Halides

Phosphorus Trichloride

i)It is a colourless oily liquid.

ii)Preparation

iii)With water,
It gets hydrolysed in the presence of moisture.

iv)Pyramidal shape, sp3 hybridisation

v)With acetic acid

vi). With alcohol

Phosphorus Pentachloride

1. Yellowish white powder.

2. Trigonalbipyramidal shape, sp3dhybridisation .

3. Preparation

4.

5. With water

6.

7. With acetic acid

8.

9. With metals

Oxoacids of Phosphorus

Hypo Phosphorous Acid (H₃PO₂) or Phosphinic Acid

It is set up by the oxidation of phosphine by iodine within the sight of figured amount of water. It is a monobasic acid.

PH₃+ 2I₂+ 2H₂O -----------> H₃PO₂+ 4 HI

Fig. 1: Hypo Phosphorous Acid

Phosphorous Acid (H₃PO₃) or Phosphonic Acid

It is set up by hydrolysis of phosphorous trioxide (P₄O₆). Phosphorous acid is dibasic in nature.

P₄O₆+ 6H₂O ----------> 4H₃PO₃

Fig. 2: Phosphorous Acid

Hypophosphoric Acid (H₄P₂O₆)

It is set up by controlled oxidation of red phosphorus with sodium chlorite arrangement when disodium salt of the hypophosphoric acid is obtained it is passed through cation exchanger to yield hypophosphoric acid. Hypophosphoric acid is tetrabasic in nature.

2P + 2NaClO₂+ 2H₂O ---------> Na₂H₂P₂O₆+ 2HCl
Na₂H₂P₂O₆+ 2H -----resin-----> H₄P₂O₆+ 2Na – resin

Fig. 3: Hypophosphoric Acid

Orthophosphoric Acid (H₃PO₄)

It is set up by treating P₄O₁₀with bubbled water. It is a tribasic acid.

P₄O₁₀+ 6H₂O ----------> 4H₃PO₄

Fig. 4: Orthophosphoric Acid

Pyrophosphoric Acid (H₄P₂O₇)

It is set up by heating orthophosphonic acid at about 250^oC. It is a tetrabasic acid.

2H₃PO₄---------> H₄P₂O₇+ H₂O

Fig. 5: Pyrophosphoric Acid

Meta Phosphoric (HPO₃)n

It is formed by warming orthophosphoric acid to around 850 K. Metaphosphoric acid does not exist as monomer. It exists as cyclic trimer, cyclic tetramer or polymer.

H₃PO₄---------> HPO₃+ H₂O

Fig. 6: Metaphosphoric Acid

The structures of oxoacids of phosphorus are efficiently given ahead:

Fig. 7: Structure of oxoacids of phosphorus with their oxidation states and basic nature