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Phosphine and Phosphorus Chloride - Practice Questions & MCQ

Edited By admin | Updated on Sep 18, 2023 18:35 AM | #JEE Main

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Reaction of thionyl chloride with white phosphorus forms a compound [A], which on hydrolysis gives [B], a dibasic acid. [A] and [B] are respectively

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Phosphine 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.

PHOSPHORUS  TRICHLORIDE

  • Preparation

It is obtained by passing dry chlorine over heated white phosphorus.
\mathrm{P_4 + 6Cl_2 \longrightarrow 4\ PCl_3}
It can also obtained by the action of thionyl chloride with white phosphorus.
\mathrm{P_4 + 8\ SOCl_2 \longrightarrow 4\ PCl_3 + 4\ SO_2+ 2\ S_2Cl_2}

  • Properties

It is a colourless oily liquid and hydrolyses in the presence of moisture.
\mathrm{PCl_3 + 3\ H_2O \longrightarrow H_3PO_3+ 3\ HCl}

It reacts with organic compounds containing –OH group and replaces it with a -Cl group 
\mathrm{RCOOH + PCl_3 \longrightarrow RCOCl+ H_3PO_3}

\mathrm{RCH_2OH + PCl_3 \longrightarrow RCH_2Cl+ H_3PO_3}

PHOSPHORUS  PENTACHLORIDE

  • Preparation

It is obtained by reaction of excess dry chlorine with white phosphorus.
\mathrm{P_4 + 10\ Cl_2 \longrightarrow 4\ PCl_5}
It can also obtained by the reaction of sulphuryl chloride with white phosphorus.
\mathrm{P_4 + 10\ SO_2Cl_2 \longrightarrow 4\ PCl_5 + 10\ SO_2}

  • Properties

It is a colourless oily liquid and hydrolyses in the presence of moisture.
\mathrm{PCl_5 + H_2O \longrightarrow POCl_3+ 2\ HCl} 
(partial hydrolysis)

\mathrm{POCl_3 + 3\ H_2O \longrightarrow H_3PO_4+ 3\ HCl} (complete hydrolysis)

It reacts with organic compounds containing –OH group and replaces it with a -Cl group 

\mathrm{RCOOH + PCl_5 \longrightarrow RCOCl+ POCl_3 + HCl}

\mathrm{RCH_2OH + PCl_5 \longrightarrow RCH_2Cl+ POCl_3 +HCl}

It can convert finely divided metals into their corresponding chlorides on heating 

\mathrm{2Ag + PCl_5 \longrightarrow 2AgCl+ PCl_3}

\mathrm{Sn +2\ PCl_5 \longrightarrow SnCl_4+ 2\ PCl_3}

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