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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

Chemistry Notes

Physics Notes

Biology Notes

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.

Phosphine Gas preparation

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 Properties

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.


Chemical Properties

Heat Effect:

Pure phosphine gas is not flammable at ordinary temperature in the presence of air, it burns when heated to about 150°C.

2PH3 + 4O2 → P2O5 + 3H2O

In the absence of air, it decomposes on heating to a temperature above 400°C.

2PH3 → 2P + 3H2

Reaction with Chlorine:

At ordinary temperature, it reacts with chlorine as follows –

PH3 + 4Cl2 → 3HCl + PCl5

Reaction with halogen acids

It reacts with halogen acids under high pressure to form phosphonium compound.

PH3 + HCl → PH4Cl (Phosphonium Chloride)

PH3 + HBr → PH4Br (Phosphonium Bromide)

PH3 + HI → PH4I (Phosphonium Iodide)

Phosphonium compounds are unstable in comparison to ammonium compounds and decompose easily.

example :

PH4I → PH3 + H+ + I

Reaction with nitric acid

It reacts with nitric acid to form phosphorus pentoxide (P2O5) and nitrogen dioxide (NO2).

[2HNO3 → 2NO2 + H2O + O] x 8

2PH3 + 😯 → P2O5 + 3H2O


2PH3 + 16HNO3 → P2O5 + 11H2O + 16NO2

It reacts with nitric acid to form phosphorus pentoxide (P2O5) and nitrogen dioxide (NO2).

Reaction with copper sulfate

A black precipitate of cupric phosphide (Cu3P2) is obtained when phosphine gas is passed through a solution of copper sulfate.

3CuSO4 + 2PH3 → Cu3P2 + 3H2SO4

Reaction with mercuric chloride:

On passing phosphine gas in a solution of murcuric chloride, a black precipitate of mercuric phosphide (Hg3P2) is obtained.

3HgCl2 + 2PH3 → Hg3P2 + 6HCl

Reaction with silver nitrate:

When passed in a solution of silver nitrate, it reduces silver nitrate to metallic silver.

6AgNO3 + 3H2O + PH3 → 6Ag + 5HNO3 + H3PO3

Reaction with metallic chlorides:

Phosphine is absorbed by anhydrous AlCl3 and anhydrous SnCl4.

AlCl3 + 2PH3 → AlCl3.2PH3

SnCl2 + 2PH3 → SnCl4.2PH3

It is also absorbed on passing through acidic solution of cuprous chloride and forms additive compound.

Cu2Cl2 + 4PH3 → Cu2Cl2.4PH3

On heating the solution, phosphine gas is again liberated.

Identification of Phosphine

Its smell is like rotten fish.

A black precipitate is obtained on passing through an aqueous solution of copper sulfate.

A black precipitate is obtained on passing through an aqueous solution of silver nitrate.

Uses of Phosphine

It is used in the preparation of phosphide compounds of various elements. Calcium phosphide (CP) is used to make the Holmes signal to signal ships in the seas. It is also used to make smoke screen in riots and wars.

For this purpose tin filled with calcium phosphide and calcium carbide is thrown into the sea. They react with water to form phosphine and acetylene gases.

Ca3P2 + 6H2O → 3Ca(OH)2 + 2PH3

Ca3C2 + 2H2O → Ca(OH)2 + C2H2

Due to the impurity of phosphorus di hydride (P2H4) in phosphine, it immediately burns up. The heat obtained in this process also burns acetylene, due to which it seems that the ocean is on fire.

The compounds formed by the burning of phosphine, acetylene and other gases, they take the form of smoke, make smoke screen or act as a signal.

Structure of Phosphine

Like ammonia, the structure of phosphine is also pyramidical. The hybridization of P is of sp3 type and phosphorus atom forms a single bond with each hydrogen atom.

The H – N – H bond angle in NH3 is 107° whereas in PH3 the H – P – H bond angle is about 93°.

Comparison of ammonia and phosphine


Both the gases are colourless. The molecular formula and molecular structures of both the gases are the same.

Both the gases do not help in the combustion of other substances. Both the gases burn on their own in the presence of oxygen.

Both the gases decompose into their constituents by electric spark.

Both react rapidly with chlorine.

Compounds with both halogen acids to form ammonium and phosphonium compounds respectively.


ammonia has a characteristic and strong odor whereas phosphine has a rotten fish-like smell.

Sniffing ammonia in excess is harmful. It is not harmful in small amounts. A small amount of ammonia is present in the atmosphere. In contrast, phosphine is a very toxic gas.

ammonia is highly soluble in water whereas phosphine is sparingly soluble in water.

ammonia is lighter in air and phosphine is heavier than air.

In ammonia, intermolecular hydrogen is bonded while phosphine does not form hydrogen bond. Due to this the boiling point of ammonia is higher than that of phosphine.

Aqueous solution of ammonia is alkaline to litmas. Aqueous solution of phosphine is neutral to litmus.

Phosphine is a weak base as compared to ammonia.

Ammonium salts are permanent compounds whereas phosphinium compounds are relatively temporary.

On passing ammonia to aqueous solution of metal salts or adding ammonium hydroxide, their hydroxides precipitate while phosphides of metals are precipitated by phosphine.

Ammonia forms complex compounds with salts of Cu(II), Ag(I) etc. whereas phosphine does not.

ammonia does not show reducing property whereas phosphine also shows reducing property.

example :

ammonia forms complex with AgNO3 while phosphine reduces AgNO3 to Ag.

These gases react with sodium to form compounds of different nature (NaNH2 and Na3P).

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