Question

Complete the following reaction:
$\text{C}{{\text{a}}_{\text{3}}}{{\text{P}}_{\text{2}}}\,\text{+}\,{{\text{H}}_{\text{2}}}\text{O}\,\,\to$

Answer 1

Metal phosphide reacting with water gives a mixture of metal hydroxide and phosphine gas.
- Calcium phosphide is red brown coloured crystalline solid which is mainly used as fireworks or to kill the rodent. This is an ionic crystalline solid have a salt like material composition of $\text{C}{{\text{a}}^{\text{2+}}}\,\text{and}\,{{\text{P}}^{\text{3-}}}$ ions.

Complete Solution :
Phosphine is prepared by the reaction of calcium phosphide with water.
$\text{C}{{\text{a}}_{\text{3}}}{{\text{P}}_{\text{2}}}\text{+}\,\,\text{6}{{\text{H}}_{\text{2}}}\text{O}\to \,\,\text{3Ca(OH}{{\text{)}}_{\text{2}}}\text{+}\,\text{2P}{{\text{H}}_{\text{3}}}$
Calcium phosphide reacts with water producing phosphine which burns in the air to give clouds of phosphorus pentoxide and that acts as smoke screens.
- Pure phosphine is non- inflammable but becomes inflammable in the presence of ${{\text{P}}_{\text{2}}}{{\text{H}}_{\text{4}}}\,\text{or}\,{{\text{P}}_{\text{4}}}$ vapours.

Additional information -
- Phosphine is a colourless gas with rotten fish smell and it is highly poisonous. It exploded in contact with trace amount of oxidizing agents like $\text{HN}{{\text{O}}_{\text{3}}}$, $\text{C}{{\text{l}}_{\text{2}}}$ and $\text{B}{{\text{r}}_{\text{2}}}$ water. This gas is slightly soluble in water. The solution of $\text{P}{{\text{H}}_{\text{3}}}$ in water decompose in presence of light giving red phosphorus and ${{\text{H}}_{\text{2}}}$.
- The spontaneous combustion of phosphine is technically used in Holme’s signals. It is also used in the production of smoke screens. $\text{Z}{{\text{n}}_{\text{3}}}{{\text{P}}_{\text{2}}}$ (zinc phosphide) is a ret poison which gives phosphine gas.

Note: Most of the metal phosphide is used as rodenticide (a chemical used to kill rodents like rats).
- Phosphine is weakly basic and like ammonia which reacts with transition metal gives metal phosphide.