Notes On Group 15: Phosphorus - Preparation Of Phosphine - CBSE Class 12 Chemistry
Phosphine is a hydride of phosphorus. It is formed in the soil by the bacterial reduction of phosphates. Methods to prepare phosphine: Phosphine can be obtained by the hydrolysis of metallic phosphides with water, or dilute mineral acids like HCl orH2SO4. Calcium phosphide or sodium phosphide on being hydrolysed with water produce phosphine.  Ca3P2 + 6 H2O→3Ca(OH)2+2PH3 Na3P +3 H2O→3NaOH+ PH3 Aluminium phosphide is hydrolysed with hydrochloric acid, it gives phosphine. AlP + 3HCl → AlCl3 + PH3 Laboratory method to prepare phosphine: In this method phosphine is prepared by hydrolysing white phosphorus with a concentrated solution of sodium hydroxide. P4 +3NaOH → 3NaH2PO2 + PH3 The origin of the flickering light, called will-o’-the-wisp is due to the spontaneous inflammation of diphosphine present in marshes. Structure: Ammonia has pyramidal geometry with a bond angle of 107.80. Similarly, phosphine is also expected to have pyramidal geometry with nearly the same or similar bond angle. But the bond angle in phosphine is only 93.50. Phosphorus has less electro-negativity than nitrogen. The electron density around the central atom phosphorus is less concentrated as compared to nitrogen in ammonia. As a result, the lone pair causes even greater distortion in phosphine. Thus, the bond angle in phosphine decreases to 93.50.

#### Summary

Phosphine is a hydride of phosphorus. It is formed in the soil by the bacterial reduction of phosphates. Methods to prepare phosphine: Phosphine can be obtained by the hydrolysis of metallic phosphides with water, or dilute mineral acids like HCl orH2SO4. Calcium phosphide or sodium phosphide on being hydrolysed with water produce phosphine.  Ca3P2 + 6 H2O→3Ca(OH)2+2PH3 Na3P +3 H2O→3NaOH+ PH3 Aluminium phosphide is hydrolysed with hydrochloric acid, it gives phosphine. AlP + 3HCl → AlCl3 + PH3 Laboratory method to prepare phosphine: In this method phosphine is prepared by hydrolysing white phosphorus with a concentrated solution of sodium hydroxide. P4 +3NaOH → 3NaH2PO2 + PH3 The origin of the flickering light, called will-o’-the-wisp is due to the spontaneous inflammation of diphosphine present in marshes. Structure: Ammonia has pyramidal geometry with a bond angle of 107.80. Similarly, phosphine is also expected to have pyramidal geometry with nearly the same or similar bond angle. But the bond angle in phosphine is only 93.50. Phosphorus has less electro-negativity than nitrogen. The electron density around the central atom phosphorus is less concentrated as compared to nitrogen in ammonia. As a result, the lone pair causes even greater distortion in phosphine. Thus, the bond angle in phosphine decreases to 93.50.

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