Question

The approximate time duration in hours to electroplate $30g$ of calcium from molten calcium chloride using a current of $5A$ is (Atomic mass of $Ca=40g/mol$)

• A. 16
• B. 10
• C. 8
• D. 80

Answer 1

The correct option is C 8

Electrolysis of molten $CaC{l}_2$
At cathode,
$C{a}^{2+}\left(aq\right)+2e^{-}\to Ca\left(s\right)$
$\text{Mass of Ca}=30g$
$\text{No. of moles of Ca}=\frac{30}{40}=0.75mol$
1 mole of $Ca$ corresponds to 2 moles of electrons. Thus, 0.75 moles of $Ca$ corresponds to,
$=0.75\times 2=1.5\text{moles of electrons}$

1 mole of electron corresponds to 96500 coulombs of electricity. $1.5$ moles of electrons will correspond to,
$=96500\times 1.5=144750\text{coloumbs of electricity}.$
Given,
$\text{Current, I}=5A$

$\text{Charge, Q}=I\times t$

$\text{Time, t}=\frac{Q}{I}$

$\text{Time, t}=\frac{144750}{5}$

$\text{Time, t}=28950s$

$\text{Time, t}=\frac{28950}{3600}=8hr$