Question

The negative Zn pole of a Daniel cell, sending a constant current through a circuit, decreases in mass by 0.13 g in 30 minutes. If the electrochemical equivalent of Zn and Cu are 32.5 and 31.5 respectively, the increase in the mass of the positive Cu pole in this time is:

• A. 0.180 g
• B. 0.141 g
• C. 0.126 g
• D. 0.242 g

Answer 1

The correct option is C 0.126 g

According to Faraday's law the amount of any substance deposited or liberated at an electrode during electrolysis is directly proportional to the quantity of current passed through the electrolyte. If $w$ is the weight or amount of a substance deposited or liberated and $A$ ampere of current is passed for $t$ seconds, $w=ZAt$

In the given cell current $A$ and time $t$ are same for $Zn$ and $Cu$ are same thus

$\frac{W_{Cu}}{W_{Zn}}$ $=\frac{Z_{Cu}}{Z_{Zn}}$

$W_{Cu}=\frac{31.5}{32.5}\times 0.13=0.126g$

Option C is correct.