The approximate time duration in hours to electroplate $30g$ of calcium from molten calcium chloride using a current of $5$ amp is: [Atomic mass of Ca $ = 40$]

Hint: The flow of current charge carriers such as electrons and electron deficient atoms is known as current. The current flows in the opposite direction of the flow of electrons. Electrons move from negative terminal to positive terminal and current moves from positive terminal to negative terminal.

Complete answer:
Let the number of moles be represented by n, given mass by m and atomic mass by M.
$n = \dfrac{m}{M}$
$ = \dfrac{{30}}{{40}}$
$ = 0.75$
The Formula of calcium chloride is $CaC{l_2}$. So, one mole of calcium corresponds to two moles of electrons. Therefore, $0.75$moles of calcium corresponds to $2 \times 0.75$$ = 1.5$moles of electrons.
We know that one mole of electron contains $96500$ coulombs of electricity. Therefore, $1.5$ moles of electrons contains $ = 96500 \times 1.5 = 144750$ coulombs of electricity.
The current given is $5$ampere. So, the time required to electroplate $30g$ of calcium is
$T=\dfrac{Q}{i}$
$ = \dfrac{{144750}}{5}$
$ = 28950$s
To convert it into hours we divide it by $3600$.
$T = \dfrac{{28950}}{{3600}}$
$T = 8$ hours

Note:
Calcium chloride is an inorganic compound. It is present as a white crystalline solid at room temperature. It is also highly soluble in water. When calcium hydroxide $\left( {Ca\left( {OH} \right){}_2} \right)$ and hydrochloric acid $\left( {HCl} \right)$ reacts with each other the formation of calcium chloride $\left( {CaC{l_2}} \right)$ takes place along with water. Calcium chloride is used to de-ice. For this process a maximum amount of calcium chloride is required. At lower temperatures, it is much more effective than sodium chloride. It is also harmless to plants and animals.