Phosphine – Structure, Properties, Preparation, Uses and FAQ

phosphine

Phosphine (PH 3 ) is a colorless, flammable, and toxic gas with a pungent odor. It is soluble in water and used as a fumigant. Phosphine gas is generated by the action of sulfuric acid on phosphorus trichloride:

Structure of Phosphine

The entire molecular structure of Phosphine is a trigonal pyramid. The diagram of Phosphine is studies based on the Lewis structure. Lewis structure is also called electron dot structures and is a picture to represent the lone pair of electrons and bonds with atoms or molecules. This can be grasped quickly using the following pointers:

• Phosphine lewis structure has 8 valence electrons.

• Since both N (Nitrogen) and P (Phosphorous) are present in the same group in the periodic table, the structure of PH3 is similar to NH3 (Ammonia).

• However, the electro-negativity of Phosphorus is lesser than that of Nitrogen.

• 93.5 is the bond angle between H-P-H regions in the structure of Phosphine.

• The bond length in P-H is 1.42 A.

Phosphine is considered to be a Lewis base. This is due to the presence of a non-bonding electrons pair on the P shell which may be donated.

Preparation of Phosphine

The preparation of Phosphine gas begins by mixing dilute Hydrochloric Acid (HCl) or water with calcium phosphide (Ca3P2). The below formula represents this preparation.

Ca3P2 + 6H2O → 3Ca(OH)2 + 2PH3

Ca3P2 + 6HCl → 3CaCl2 + 2PH3

As you might have noticed, the other results along with Phosphine are Calcium Hydroxide (in the case of water) and Calcium Chloride (in the case of hydrochloric acid).

The laboratory preparation of Phosphine goes by the following case:

P4+3NaOH+3H2O → PH3 + 3NaH2PO2

Here, White Phosphorus has to be heated with concentrated Sodium Hydroxide to gove out Phosphine. Note that this preparation has to be undertaken in an inert atmosphere to make use of Carbon dioxide (CO2).

Physical and chemical properties of Phosphine

Physical properties of Phosphine are given below:

• Formula – PH3

• Critical Temp. (°F) – 124.9

• Density of the gas @ 70°F 1 atm (lb/ft3) – 0.0885

• Specific Gravity – 1.203

• Melting Point (°F) – 208.8

• Boiling Point (°F) – 126.0

• Molecular Weight (lb/mol) – 34.00

• Critical Pressure (Pc) – 947.9

• Liquid Density @ 70°F (lb/ft3) – 35.5