Phosphine

Phosphine - PH3:

Phosphine is best acknowledged hydride of phosphorus.

Laboratory preparation:

It is generally obtained by boiling white phosphorus with 30 to 40 percent solution of caustic soda in an inert atmosphere of CO2.

4P + 3NaOH + 3H2O → PH3 + 3NaH2PO2
                                 Sodium hypophosphite

Phosphine thus obtained is impure. It is then passed into an aqueous solution of hydrogen iodide, PH4I is created. PH4I is heated with KOH or NaOH, pure phosphine is acquired.

PH3 + HI → PH4I
PH4I + NaOH → PH3 + NaI + H2O

Physical properties:

Phosphine is a colorless gas with rotten fish odor.

Chemical properties:

1. Dissociation:

Phosphine dissociates at around 723 K and provides red phosphorus.
 
2. Action of air:

It burns with oxygen and generates phosphorus pentoxide.

4PH3 + 8O2 → P4O10 + 6H2O

3. Action of chlorine:

Phosphine burns in chlorine suddenly forming, PCl3 and PCl5.

PH3 + 3Cl2→ PCl3 + 3HCl
PH3 + 4Cl2 → PCl5+ 3HCl

4. Reducing properties:

PH3 is a powerful reducing agent. Whenever it is passed via the salt solutions, corresponding metal is made.

PH3 + 6AgNO3 + 3H2O → 6Αg + 6HNO3 + H3PO3

Uses:

1. Smoke screens:

Whenever PH3 burns it generates smoke which is dense sufficient to serve as smoke screens.

2. Holme’s signal:

Containers that have a perforated bottom and a hole at the top are filled with calcium phosphide and calcium carbide. These both are thrown into the sea. Water enters the container via the bottom and reacts with calcium carbide and calcium phosphide to provide acetylene and phosphine. Phosphine acquires ignited spontaneously as it comes in contact with air and as well ignites acetylene.

Therefore a bright red flame is produced that is accompanied by enormous smoke due to the burning of phosphine. This serves up as a signal to the approaching ships.

Ca3P2 + 6H2O → 2 PH3↑ + 3Ca (OH)2
CaC2 +2H2O → C2 H2 ↑ + Ca (OH)2

 

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