Question

How much electricity in terms of Faraday is required to produce:

(i) $20g$ of $Ca$ from molten $CaC{l}_2$
(ii) $40g$ of $Al$ from molten $A{l}_2{O}_3$

[Given : Molar mass of calcium & Aluminium are 40 g $mo{l}^{-1}$ & 27 g $mo{l}^{-1}$ respectively]

Answer 1

$\left(1\right)$ $C{a}^{2+}+2e^{-}\to Ca$

$1$ mole ($40$ g) of $Ca$ will require $2$ F of electricity.
$20$ g ($0.5$ mole) of $Ca$ will require $1$ F of electricity.

(2) $A{l}^{3+}+3e^{-}\to Al$

$1$ mole ($27$ g) of $Al$ will require $3$ moles of electrons.
$40$ g of $Al$ will require $\frac{3\times 40F}{27}=4.4$ F