Question

Choose the correct statement about electrolysis?

• A. For an equal amount of charge is passed through two different solutions ,the amount of substance deposited/liberated is proportional to their chemical equivalent weights
• B. For an equal amount of charge is passed through two different solutions ,the amount of substance deposited/liberated is proportional to their molecular mass
• C. $\text{Current efficiency}=\frac{\text{Charge actually used in electricity}}{\text{Charge passed}}$
• D. Both (a) and (c)

Answer 1

The correct option is D Both (a) and (c)

Farday's second law:
For an equal amount of charge (Q) is passed through two different solutions ,the amount of substance deposited/liberated (W) is proportional to their chemical equivalent weights (E)
Considering two electrolytic cells, 1 and 2 in which same charge (Q) is passed
Applying Faraday's first law:
$W_1=Z_1\times Q$
$W_2=Z_2\times Q$

Dividing both

$\frac{W_1}{W_2}=\frac{Z_1}{Z_2}$

$\frac{W_1}{W_2}=\frac{E_1\times F}{F\times E_2}$

Here
$E_1\&E_2$ are equivalent weights
$\therefore \frac{W_1}{W_2}=\frac{E_1}{E_2}$

Example:
Considering two electrolytic cells, 1 and 2, for electrolysis of $Cu$ and $Ag$ respectively as shown. Equal current for a equal duration is provided in both.


As shown,
$\frac{W_1}{W_2}=\frac{31.75}{108}$

Also,
$\frac{E_1}{E_2}=\frac{31.75}{108}$

Thus,
$\frac{W_1}{W_2}=\frac{E_1}{E_2}$

$\text{Current efficiency}=\frac{\text{Mass actually produced}}{\text{Mass that should have been produced}}$

$\text{Current efficiency}=\frac{\text{Charge actually used in electricity}}{\text{Charge passed}}$