Phosphine Gas

Phosphine Gas: Preparation, formula, and Uses

Chemical Formula

  • Copper pyrites – CuFeS2
  • Meta Phosphoric Acid – HPO3
  • Lead Sulphide – PbS
  • Hematite – Fe2O3
  • Silicon Dioxide – SiO2
  • Magnesium Carbonate – MaCO

Phosphine gas was discovered by Philippe Gengembre in 1783. Gengembre made it by the action of caustic soda on phosphorus. It is chemical formula PH3.

Phosphine Gas Preparation

Phosphides – When calcium and sodium Phosphides reacts with water, phosphine gas is obtained.

Ca3P2 + 6H2O 3Ca(OH)2 + 2PH3

Ca3P + 3H2O 3CaOH + PH3

Phosphine gas is also obtained by the action of dilute sulfuric acid from aluminium phosphide.

2AlP + 3H2SO4 Al2(SO4)3 + 2PH3

Phosphine gas is formed by the action of phosphonium iodide with sodium hydroxide.

PH4I + NaOH PH3 + NaI + H2O

Phosphine gas can also be made by heating phosphorus acid.

4H3PO3 3H3PO4 + PH3

Phosphine gas is formed by heating white phosphorus with concentrated caustic soda.

4P + 3NaOH + 3H2O 3NaH2PO2 + PH3

This method of making phosphine is used for manufacture in its laboratory. To make this gas in the laboratory, in a round bottomed flask, a few pieces of white phosphorus and a mixture of sodium hydroxide of about 40% concentrations are first heated slowly and then rapidly.

This device is air tight and the cork on the mouth of the flask has two tubes. One of these flows coal gas through the tube, displacing the air in the flask. Oxygen of air can lead to unnecessary charges from reactants and products.

Whereas coal gas does not do this. Shortly after the reaction begins, the flow to the coal gas is stopped. The second tube in the flask exits the phosphine gas. If the other end of this second tube is immersed in water, the gas coming out of the water makes white smoke rings.

This is due to the phosphorus hydrides(P2H4). Phosphorus hydrides gas (Diphosphane) rises as it comes in contact with air. White smoke is obtained due to the formation of Meta Phosphoric Acid(HPO3).

6P + 4NaOH + 4H2O 4NaH2PO2 + P2H4

2P2H4 + 7O2 4HPO3 + 2H2O

In order to obtain pure phosphine gas, the gaseous mixture obtained from the exhaust pipe is flowed through the ice water. Where the impurities are condensed and separated and the pure phosphine gas is collected by downward displacement of water.

In the above method, pure phosphine gas is obtained by using an alkaline solution of KOH in place of aqueous NaOH solution.

Phosphine: Physical Properties

It is a colorless, century fish-like odor and poisonous gas.

It changes into a liquid state at – 85°C and a solid state at – 135°C.

It is a small amount of fusion in water and heavier than air.

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