Question

When ${\text{P}}{{\text{H}}_{\text{3}}}$ absorbed in ${\text{HgC}}{{\text{l}}_{\text{2}}}$ solution the corresponding phosphide is obtained
A. ${\text{H}}{{\text{g}}_{\text{2}}}{{\text{P}}_{\text{3}}}$
B. ${\text{H}}{{\text{g}}_{\text{3}}}{{\text{P}}_{\text{2}}}$
C. ${\text{H}}{{\text{g}}_{\text{3}}}{\left( {{\text{P}}{{\text{O}}_{\text{4}}}} \right)_{\text{2}}}$
D. None of these

Answer 1

Hint: Phosphine when absorbed in mercuric chloride solution results in the formation of corresponding phosphides along with hydrochloric acid. Phosphine is weakly basic in nature and phosphonium compounds are formed with acids.

Complete step by step answer:
In the presence of light phosphine decomposes in water giving red phosphorous and ${{\text{H}}_{\text{2}}}$ and when it is absorbed in copper sulphate or mercuric chloride solution, the corresponding phosphides are obtained.
${\text{3CuS}}{{\text{O}}_{\text{4}}}{\text{ + 2P}}{{\text{H}}_{\text{3}}}\xrightarrow{{}}{\text{C}}{{\text{u}}_{\text{3}}}{{\text{P}}_{\text{2}}}{\text{ + 3}}{{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}$
When ${\text{P}}{{\text{H}}_{\text{3}}}$ is absorbed in${\text{HgC}}{{\text{l}}_{\text{2}}}$solution${\text{H}}{{\text{g}}_{\text{3}}}{{\text{P}}_{\text{2}}}$is formed
\[{\text{3HgC}}{{\text{l}}_{\text{2}}}{\text{ + 2P}}{{\text{H}}_{\text{3}}}\xrightarrow{{}}{\text{H}}{{\text{g}}_{\text{3}}}{{\text{P}}_{\text{2}}}{\text{ + 6HCl}}\]
Mercury phosphide precipitate is formed.

So, the correct answer is Option B.

Additional information:
Phosphine is a colourless gas which has an odour of rotten fish and it is highly poisonous in nature. It explodes when it comes in contact with traces of oxidising agents like ${\text{HN}}{{\text{O}}_{\text{3}}}$,${\text{C}}{{\text{l}}_{\text{2}}}$ and ${\text{B}}{{\text{r}}_{\text{2}}}$ vapours. It is slightly soluble in water. Basicity of Phosphine is weakly basic in nature and like ammonia; it gives phosphonium compounds with acids
E.g., ${\text{P}}{{\text{H}}_{\text{3}}}{\text{ + HBr}}\xrightarrow{{}}{\text{P}}{{\text{H}}_{\text{4}}}{\text{Br}}$
Phosphine reacts with acids such as ${\text{HI}}$ to form ${\text{P}}{{\text{H}}_{\text{4}}}{\text{I}}$ which shows that it is basic in nature
${\text{P}}{{\text{H}}_{\text{3}}}{\text{ + HI}}\xrightarrow{{}}{\text{P}}{{\text{H}}_{\text{4}}}{\text{I}}$
Due to the presence of lone pair of electrons on phosphorus atom, ${\text{P}}{{\text{H}}_{\text{3}}}$ acts as Lewis base in the above reaction.

Note: Pure Phosphine is inflammable but it becomes flammable in the presence of ${{\text{P}}_{\text{2}}}{{\text{O}}_{\text{4}}}$ or ${{\text{P}}_{\text{4}}}$ vapours. Purification of phosphine from the impurities is done when it is absorbed in ${\text{HI}}$ to form phosphonium iodide which on further treatment with ${\text{KOH}}$ gives off phosphine.