Question

The equivalent weight of copper and silver are 32 and 108 respectively. When copper and silver voltameter are connected in series and electric current is passed through for sometimes, $1.6g$ of copper is deposited. Then, the mass of silver deposited will be:

• A. $3.5g$
• B. $2.8g$
• C. $5.4g$
• D. $8g$

Answer 1

The correct option is C $5.4g$

If 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).

For copper cell,
By Faradays first law,
$W_1=Z_1\times Q_1$
where,
$W_1=\text{Amount of copper deposited}{Z}_1=\text{Electrochemical equivalent of copper}{Q}_1=\text{Charge passed through the copper cell}$

For Silver cell,
By Faradays first law,
$W_2=Z_2\times Q_2$
where,
$W_2=\text{Amount of silver deposited}{Z}_2=\text{Electrochemical equivalent of silver}{Q}_2=\text{Charge passed through the silver cell}$

Since, charge passed is same for both the cells,
$Q_1=Q_2$

So,

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

$Z_1=\frac{E_1}{96500}{Z}_2=\frac{E_2}{96500}$

$\therefore$

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


$E_1=\text{chemical equivalent weight of copper}{E}_2=\text{chemical equivalent weight of silver}$

$\therefore \frac{W_2}{W_1}=\frac{E_2}{E_1}\Rightarrow W_2=\frac{108}{32}\times 1.6=5.4g$