Properties of phosphine:
- Phosphine is a colourless and extremely poisonous gas that smells like garlic or rotten fish.
- It is slightly soluble in water and the aqueous solution is neutral. It is more soluble in carbon disulphide and other organic solvents.
- The melting and boiling points of phosphine are much less than that of ammonia due to the absence of hydrogen bonding. It condenses to a colourless liquid at -870c and freezes at -1320c.
- Phosphine acts as a Lewis base. It is a weaker base than ammonia because its central atom phosphorus is larger in size and less electro-negative.
- Phosphine combines with hydrogen iodide, thereby acting as a Lewis base by donating its lone pair to form phosphonium iodide salt.
- Pure phosphine is non-combustible at normal conditions, but catches fire when heated to about 1500 to form phosphoric acid.
When phosphine is heated to about 4400
c in an inert atmosphere, or when it is subjected to an electric spark, it decomposes into phosphorus and hydrogen.
Inner Atmosphere Red Phosphorus Hydrogen
4PH3 → P4 + 6H2
Red Phosphorus Hydrogen
An aqueous solution of phosphine decomposes in the presence of light into red phosphorus and hydrogen.
4PH3 (aq) → P4 + 6H2
Phosphine Red Phosphorus Hydrogen
It burns with an explosion when it comes in contact with even small amounts of oxidising agents.
It burns with an explosion when it comes in contact with even small amounts of oxidising agents such as nitric acid and chlorine gas.
Phosphine Nitric Acid Phosphorus Nitrogen
PH3 + 4Cl2 → PCl5 + 3HCl
Phosphine Chlorine Phosphorus Hydrochloric
When passed through aqueous metallic salt solutions such as copper sulphate, silver nitrate and mercuric chloride, phosphine gas precipitates the corresponding metal phosphides.
↓ + 3H2
Copper Phosphine Copper Sulphuric
Sulphate Phosphide Acid
3AgNO3 + PH3 → Ag3P ↓ + 3HNO3
Silver Phosphine Silver Nitric
Nitrate Phosphide Acid
3HgCl2 + 2PH3 → Hg3P2 ↓ + 6HCl
Mercuric Phosphine Mercuric Hydrochloric
Chloride Phosphide Acid
Uses of phosphine:
It finds use in the manufacture of Holme’s signals and smoke screens.