Question

In which of the following, a white precipitate of AgCl dissolves in excess?

$$\left( {\text{I}} \right){\text{ N}}{{\text{H}}_3}{\text{(aq)}} \\\ \left( {{\text{II}}} \right){\text{ N}}{{\text{a}}_2}{{\text{S}}_2}{{\text{O}}_3} \\\ \left( {{\text{III}}} \right){\text{ NaCN}} \\\$$

${\text{A}}{\text{.}}$ III only
${\text{B}}{\text{.}}$ I, II, III
${\text{C}}{\text{.}}$ I, II
${\text{D}}{\text{.}}$ I only

Answer 1

Here, we will proceed by making balanced chemical reactions in all the three cases mentioned in the problem. If the products formed which will be soluble in the solution which means that they are stable and hence, the white precipitate of AgCl are dissolved in excess quantities of these.

Complete answer:
$\left( {\text{I}} \right)$ When a white precipitate of silver chloride (AgCl) is dissolved in excess aqueous ammonia (which is a solution of ${\text{N}}{{\text{H}}_3}$ in water resulting in formation of ammonium hydroxide i.e.,${\text{N}}{{\text{H}}_4}{\text{OH}}$), Diammine Silver(I) Chloride (i.e., $\left[ {{\text{Ag}}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_2}} \right]{\text{Cl}}$) which is soluble is formed along with water molecules (${{\text{H}}_2}{\text{O}}$). The balanced chemical reaction is shown below.

$${\text{N}}{{\text{H}}_3} + {{\text{H}}_2}{\text{O}} \to {\text{N}}{{\text{H}}_4}{\text{OH}} \\\ {\text{AgCl}} + 2{\text{N}}{{\text{H}}_4}{\text{OH}} \to \left[ {{\text{Ag}}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_2}} \right]{\text{Cl}} + {\text{2}}{{\text{H}}_2}{\text{O}} \\\$$

$\left( {{\text{II}}} \right)$ When a white precipitate of silver chloride (AgCl) is dissolved in excess Sodium thiosulfate (${\text{N}}{{\text{a}}_2}{{\text{S}}_2}{{\text{O}}_3}$), Sodium bis thiosulphate agentate (i.e.,${\text{N}}{{\text{a}}_3}\left[ {{\text{Ag}}{{\left( {{{\text{S}}_2}{{\text{O}}_3}} \right)}_2}} \right]$) which is soluble is formed along with sodium chloride (${\text{NaCl}}$). The balanced chemical reaction is shown below.
${\text{2AgCl}} + 4{\text{N}}{{\text{a}}_2}{{\text{S}}_2}{{\text{O}}_3} \to 2{\text{N}}{{\text{a}}_3}\left[ {{\text{Ag}}{{\left( {{{\text{S}}_2}{{\text{O}}_3}} \right)}_2}} \right] + 2{\text{NaCl}}$
$\left( {{\text{III}}} \right)$ When a white precipitate of silver chloride (AgCl) is dissolved in excess Sodium cyanide (NaCN), Sodium dicyanoargentate (i.e.,${\text{Na}}\left[ {{\text{Ag}}{{\left( {{\text{CN}}} \right)}_2}} \right]$) which is soluble is formed along with sodium chloride (${\text{NaCl}}$). The balanced chemical reaction is shown below.
${\text{AgCl}} + 2{\text{NaCN}} \to {\text{Na}}\left[ {{\text{Ag}}{{\left( {{\text{CN}}} \right)}_2}} \right] + 2{\text{NaCl}}$
Here, all the products formed in all the three cases are soluble which means they are stable.
Therefore, a white precipitate of AgCl dissolves in excess of all three ${\text{N}}{{\text{H}}_3}{\text{(aq),N}}{{\text{a}}_2}{{\text{S}}_2}{{\text{O}}_3}$ and NaCN.

Hence, option B is correct.

Note:
The most effective form of water- activated battery uses magnesium as the anode and silver chloride as the positive electrode. Silver chloride is also used in electroplating and polishing mirrors and in making alloys. Silver chloride is used as an antidote that reacts with the poison to produce a harmless chemical compound.