Question

A certain metal salt solution is electrolysed in series with a silver coulometer. The weights of silver and the metal deposited are 0.5094 g and 0.2653 g calculated the valency the valency of the metal if its atomic weight is nearly that of silver.

• A. 1
• B. 2
• C. 3
• D. 4

Answer 1

Answer: (B)

2

According to Faraday's second law of electrolysis, the masses of different ions liberated at electrodes in electrolysis are directly proportional to their chemical equivalent, when the same amount of current passe through different electrolytes

Since two solution are connected in series, the same amount of current flows through them.

thus we can use Faraday's second law

Mass of silver deposited$W_{Ag}=0.5094g$

Mass of metaldeposited$W_x=0.2653g$

Molar mass of silver $=107.8682u$

Molar mass of metal $\approx 107.8682$

Equivalent mass of silver$=\frac{Molarmass}{Valency}=\frac{107.8682}{1}=107.8682$

Equivalent mass of silver$=\frac{Molarmass}{Valency}=\frac{107.8682}{x}$

Now,

$\frac{W_{Ag}}{W_x}=\frac{E_{Ag}}{E_x}$

$\frac{0.5094}{0.2653}=\frac{107.88682\times x}{107.8682}$

$x=1.92\approx 2$

Thus, the valency of metal is 2