Question

$Cd$ amalgam is prepared by electrolysis of a solution $CaC{l}_2$ using a mercury cathode. The time (in a sec) for which a current of $5A$ should be passed in order to prepare $12$ % $Cd-Hg$ amalgam on a cathode of $2gHg$ is ______

Atomic weight of $Cd=112.4$. (write the value to the nearest integer)

Answer 1

Let w g be the mass of Cd in 12% Cd-Hg amalgam on a cathode of 2 g , Hg
$\frac{w}{w+2}\times 100=12\frac{w}{w+2}=0.12w=0.12w+0.240.88w=0.24w=0.2727g$
The molar mass of Cd is 112.4 g/mol
Number of moles of Cd $=\frac{0.2727g}{112.4g/mol}=0.002426$
1 mole of Cd corresponds to 2 moles of electrons.
0.002426 moles of Cd corresponds to
$0.002426\times 2=0.00485$ moles of electrons
$0.00485=\frac{I\left(A\right)\times t\left(s\right)}{Faraday}0.00485=\frac{5\times t\left(s\right)}{96500}t\left(s\right)=93.65$