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Notes on Phosphorus

566 / May-30-2021 12:03:14 By- srijan /


1. Phosphorus:
Symbol: P
Molecular Formula: P4
Atomic number: 15
Valency: 3,5

Allotropes of phosphorus:

i) White or yellow phosphorus
ii) Red phosphorus
iii) Black phosphorus
iv) Scarlet phosphorus
v) Violet phosphorus

1. White Phosphorus:
* Physical Properties:
(i) It is white waxy solid with garlic smell.
(ii) It is poisonous.
(iii) It is insoluble in water but soluble in organic solvents like benzene, chloroform, etc.
(iv) Melting point 44oC, boiling point 280oC, specify gravity= 1.81.
(v) It turns yellow when exposed to light. So, it is also called yellow phosphorus.
(vi) It catches fire in air to form white fumse spontaneously.

* Chemical Properties:
(i) Action with heat: When white phosphorus is heated at 250oC in the atmosphere of nitrogen and
carbondioxide in presence of catalyst iodine (I2), red phosphorus is formed.
White phosphorus  Red phosphorus

(ii) Action with air: When phosphorus is exposed to air, it burns with white fumes to give P4O10.
P4 + 3O2 -------> P4O6 (Phosphorus trioxide)
P4 + 5O2 -------> P4O10 (Phosphorus pentoxide)

(iii) Action with alkalis:
P4+NaOH  NaH2PO2 + PH3
P4+NaOH  KH2PO2 + PH3

(iv) Reduction Behaviour:
P4 + 10H2SO4(conc.) ---------> 4H3PO4(phosphoric acid) + 4H2O + 10SO2
P4 + 10HNO3(conc.) ---------> 4H3PO4(phosphoric acid) + 3H2O + NO2

1. It is used as rat poison.
2. It is used to prepare phosphoric acid, phosphonine gas, red phosphorus.

2. Red Phosphorus:

Uses of red phosphorus:
1. Red phosphorus is used for manufacture of matchstick.
2. It is used to prepare phosphorus bronze (an alloy of P with Sn and Cu).

Phosphine (PH3)
In laboratory, phosphine gas is prepared by the action of white phosphorus with aqueous caustic soda.
P4 + 3NaOH + 3H2O  3NaH2PO2 + PH3

Laboratory preparation of Phosphine gas:

Purification of this gas:
Impure (phosphine gas) PH3 is purified by treating it with hydrogen iodide (HI) followed by the heating with
NaOH solution.
PH3 + HI  PH4I (phosphonium iodide)
PH4I + NaOH  NaI + PH3 + H2O

Chemical Properties:
(i) Combustibility: Like ammonia, PH3 is also non-supporter of combustion.
4PH3 + 8O2 --------> P4O10 + 6H2O
PH3 + 3O2 --------> H3PO4

(ii) Decomposition: It is less stable than ammonia.
4PH3  P4(red) + 6H2

(iii) Basic nature:
PH3 is weaker base then ammonia. It is neutral to litmus paper.
NH3 + H2O ---------> NH4OH
NH4OH  NH4+ + OH-
PH3 + H2O ------> PH4OH
PH4OH  PH4+ + OH-

(iv) Reducing nature:
6AgNO3 + PH3 + H2O -------> 6Ag + H3PO3(phosphorus acid) + 6HNO3

Phosphorus acid

1. It is used to prepare phosphine gas.
2. It is used as strong reducing agent.

Phosphoric acid:

1. It is used to manufacture chemical fertilizer.
2. It is used to manufacture medicines etc.

3. Black Phosphorus:
Physical properties
1. It is black crystaline solid.
2. It doesnot burn in air.

4. Scarlet Phosphorus:
1. It's properties resembled with red phosphorus.
2. It is obtain in powder form.

5. Violet Phosphorus:
1. It is obtained by heating red phosphorus.