Question

Which of the following has least conductivity in aqueous solution?
A.$\left[ {Co{{\left( {N{H_3}} \right)}_4}C{l_3}} \right]$
B.$\left[ {Co{{\left( {N{H_3}} \right)}_3}C{l_3}} \right]$
C.$\left[ {Co{{\left( {N{H_3}} \right)}_5}C{l_3}} \right]$
D.$\left[ {Co{{\left( {N{H_3}} \right)}_6}C{l_3}} \right]$

Answer 1

In an electrolyte solution two electrodes are immersed, then voltage Is applied to these two electrodes which results in motion of ions of electrolytes present in the solution. Conductivity is defined as the power of these electrolytes formed in solution to conduct electricity.

Complete answer:
Electrolytic conductivity of solution depends upon the total number of ions present in the solution.
$\left[ {Co{{\left( {N{H_3}} \right)}_4}C{l_3}} \right]$ This compound when dissolved in aqueous medium it undergoes hydrolysis to form ions $Co{\left( {N{H_3}} \right)_4}C{l^ + }$and $C{l^ - }$.
$\left[ {Co{{\left( {N{H_3}} \right)}_4}C{l_3}} \right] \to$ $Co{\left( {N{H_3}} \right)_4}C{l^ + } + C{l^ - }$
In aqueous solution it forms one ion of $Co{\left( {N{H_3}} \right)_4}C{l^ + }$ and one ions of chloride atom $C{l^ - }$ Hence, conductivity of this compound is due to presence of these two types of ions.
$\left[ {Co{{\left( {N{H_3}} \right)}_3}C{l_3}} \right]$ This compound when dissolved in aqueous medium it undergoes hydrolysis to form ions.
$\left[ {Co{{\left( {N{H_3}} \right)}_3}C{l_3}} \right] \to \left[ {Co{{\left( {N{H_3}} \right)}_3}C{l_3}} \right]$
In aqueous solution it forms only one ion of $\left[ {Co{{\left( {N{H_3}} \right)}_3}C{l_3}} \right]$
Hence, conductivity of this compound is due to the presence of only one type of ion.
$\left[ {Co{{\left( {N{H_3}} \right)}_5}C{l_3}} \right]$ This compound when dissolved in aqueous medium it undergoes hydrolysis to form ions
$\left[ {Co{{\left( {N{H_3}} \right)}_5}C{l_3}} \right] \to$ $Co{\left( {N{H_3}} \right)_5}C{l^{ + 2}} + 2C{l^ - }$
In aqueous solution it forms one ion of $Co{\left( {N{H_3}} \right)_5}C{l^{ + 2}}$ and two ions of chloride atom $C{l^ - }$.
Hence, conductivity of this compound is due to the presence of these three types of ions.
$\left[ {Co{{\left( {N{H_3}} \right)}_6}C{l_3}} \right]$-This compound when dissolved in aqueous medium it undergoes hydrolysis to form ions
$\left[ {Co{{\left( {N{H_3}} \right)}_6}C{l_3}} \right] \to$ ${\left( {Co{{\left( {N{H_3}} \right)}_6}} \right)^{ + 3}} + 3C{l^ - }$
In aqueous solution it forms one ion of ${\left( {Co{{\left( {N{H_3}} \right)}_6}} \right)^{ + 3}}$ and three ions of chloride atom $C{l^ - }$ Hence, conductivity of this compound is due to presence of these four types of ions.
From the above discussion we see that option(iv) $\left[ {Co{{\left( {N{H_3}} \right)}_6}C{l_3}} \right]$ generate the maximum number of ions and therefore has maximum conductance in aqueous solution.

Note:
Conductance due to presence of ions is commonly known as electrolytic conductance while conductance due to electron movement is known as metallic conductance.
On increasing the temperature value of electrolytic conductance increases due to increase in kinetic energy of ions in solution.