Phosphine and Phosphorus Chloride MCQ - Practice Questions & Answers

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Phophine and Phosphorus Chloride

PHOSPHINE

Preparation
Phosphine is prepared by the reaction of calcium phosphide with water or dilute HCl.
$\mathrm{Ca_{3}P_{2}\: +\: 6H_{2}O\: \rightarrow \: 3Ca(OH)_{2}\: +\: 2PH_{3}}$
$\mathrm{Ca_{3}P_{2}\: +\: 6HCl\: \rightarrow \: 3CaCl_{2}\: +\: 2PH_{3}}$
In the laboratory, it is prepared by heating white phosphorus with concentrated NaOH solution in an inert atmosphere of CO₂.
$\mathrm{P_{4}\: +\: 3NaOH\: +\: 3H_{2}O\: \rightarrow \: PH_{3}\: +\: 3NaH_{2}PO_{2}}$
When pure, it is non-inflammable but becomes inflammable owing to the presence of P₂H₄ or P₄ vapours. To purify it from the impurities, it is absorbed in HI to form phosphonium iodide (PH4I) which on treating with KOH gives off phosphine.
$\mathrm{PH_{4}I\: +\: KOH\: \rightarrow \: KI\: +\: H_{2}O\: +\: PH_{3}}$
Properties
It is a colourless gas with the rotten fish smell and is highly poisonous. It explodes on contact with traces of oxidising agents like HNO₃, Cl₂ and Br₂ vapours. It is slightly soluble in water. The solution of PH₃ in water decomposes in presence of light giving red phosphorus and H₂.When absorbed in copper sulphate or mercuric chloride solution, the corresponding phosphides are obtained.
$\mathrm{3CuSO_{4}\: +\: 2PH_{3}\: \rightarrow \: Cu_{3}P_{2}\: +\: 3H_{2}SO_{4}}$
$\mathrm{3HgCl_{2}\: +\: 2PH_{3}\: \rightarrow \: Hg_{3}P_{2}\: +\: 6HCl}$
Uses
The spontaneous combustion of phosphine is technically used in Holme’s signals. Containers containing calcium carbide and calcium phosphide are pierced and thrown in the sea when the gases evolved burn and serve as a signal. It is also used in smoke screens.