Question

A mixture of which pair of species react with water to produce a pure colourless gas that gives white fumes with HCl?
A. calcium hydride and calcium carbide
B. calcium carbide and aluminium nitride
C. magnesium nitride and calcium nitride
D. calcium phosphate and calcium cyanamide

Answer 1

We have to find out the compounds that react with water and give a gas. We will write the hydrolysis reaction of all the given compounds and determine the gaseous product. Then we will check the colour of the gas because the gas should be colourless. After that we will write the reaction of the gaseous product with HCl to determine the product giving white fumes. The given compounds produce hydrogen, ammonia and phosphine gases. All are colourless and only ammonia gives the white fumes with HCl. So, we will find the pair gives ammonia gas.

Complete solution:
The reaction of calcium hydride and calcium carbide with water is as follows:
${\text{Ca}}{{\text{H}}_{\text{2}}}\, + \,2\,{{\text{H}}_2}{\text{O}} \to \,{\text{Ca(OH}}{{\text{)}}_2}\, + \,2\,{{\text{H}}_2}$
${\text{Ca}}{{\text{C}}_{\text{2}}}\, + \,2\,{{\text{H}}_2}{\text{O}} \to \,{\text{Ca(OH}}{{\text{)}}_2}\, + \,{{\text{C}}_{\text{2}}}{{\text{H}}_2}$
So, the calcium hydride produces hydrogen gas and calcium carbide produces acetylene gas. Both are colourless gas.
Hydrogen does not react with HCl and acetylene gives electrophilic addition reaction with HCl. So, option (A) is not correct.
The reaction of calcium hydride and aluminium nitride with water is as follows:
${\text{Ca}}{{\text{C}}_{\text{2}}}\, + \,2\,{{\text{H}}_2}{\text{O}} \to \,{\text{Ca(OH}}{{\text{)}}_2}\, + \,{{\text{C}}_{\text{2}}}{{\text{H}}_2}$
${\text{AlN}}\, + \,3\,{{\text{H}}_2}{\text{O}} \to \,{\text{Al(OH}}{{\text{)}}_3}\, + \,{\text{N}}{{\text{H}}_3}$
So, the calcium carbide produces acetylene gas and aluminium nitride produces ammonia gas. Both are colourless gas.
Acetylene gives electrophilic addition reaction with HCl and ammonia in reaction with HCl gives white fumes of ammonium chloride. But calcium hydride does not give products that produce white fumes so, option (B) is not correct.
The reaction of magnesium nitride and calcium nitride with water is as follows:
${\text{M}}{{\text{g}}_3}{{\text{N}}_{\text{2}}}\, + \,6\,{{\text{H}}_2}{\text{O}} \to \,3\,{\text{Mg(OH}}{{\text{)}}_2}\, + \,2{\text{N}}{{\text{H}}_3}$
${\text{C}}{{\text{a}}_3}{{\text{N}}_{\text{2}}}\, + \,6\,{{\text{H}}_2}{\text{O}} \to \,3\,{\text{Ca(OH}}{{\text{)}}_2}\, + \,2{\text{N}}{{\text{H}}_3}$
So, the magnesium nitride and calcium nitride both give ammonia gas and ammonia is a colourless gas.
Ammonia in reaction with HCl gives white fumes of ammonium chloride.
${\text{N}}{{\text{H}}_{\text{3}}}\,{\text{ + }}\,{\text{HCl}}\,\, \to \,{\text{N}}{{\text{H}}_{\text{4}}}{\text{Cl}}$
So, option (C) is correct.
The reaction of calcium phosphate and calcium cyanamide with water is as follows:
${\text{C}}{{\text{a}}_3}{{\text{P}}_{\text{2}}}\, + \,6\,{{\text{H}}_2}{\text{O}} \to \,3\,{\text{Ca(OH}}{{\text{)}}_2}\, + \,2{\text{P}}{{\text{H}}_3}$
${\text{CaC}}{{\text{N}}_{\text{2}}}\, + \,3\,{{\text{H}}_2}{\text{O}} \to \,{\text{CaC}}{{\text{O}}_2}\, + \,2{\text{N}}{{\text{H}}_3}$
So, the calcium phosphide produces phosphine gas and calcium cyanamide produces ammonia gas. Both are colourless gas.
Phosphine does not react with HCl and ammonia on reaction with HCl gives white fumes of ammonium chloride. But calcium phosphide does not give products that produce white fumes so, option (D) is not correct.
So, the mixture of magnesium nitride and calcium nitride react with water to produce a pure colourless gas that gives white fumes with HCl.

Therefore, option (C) magnesium nitride and calcium nitride, is correct.

Note: Carbides are complex composed of metals and carbon. The carbides that contain ${\left[ {{{\text{C}}_2}} \right]^{2 - }}$are known as acetylides or euthymides. ${\text{Ca}}{{\text{C}}_2}$ is an acetylides. Acetylides on hydrolysis gives acetylene. Ammonium chloride is a water soluble compound. It gives ammonia and chloride gas on dissolving in water. Ammonium chloride is used to treat the urinary stones in animals.