Question

$1000mL$ of $1MCuS{O}_4\left(aq\right)$ is electrolysed by $9.65$ ampere current for $100s$ using $Pt-$ electrode. Which of the following statement is correct?
[ Equivalent weight of $O_2$ is 8 g]

• A. Blue colour intensity of solution decreases during electrolysis
• B. Blue colour intensity of solution increases during electrolysis
• C. Blue colour intensity of solution remains constant during electrolysis
• D. Blue colour intensity of solution remains increases if copper electrode is used

Answer 1

The correct option is A Blue colour intensity of solution decreases during electrolysis

Given:
$1000mL$ of $1MCuS{O}_4\left(aq\right)$ is elecrolysed by $9.65A$ current for $100s$ using platinum electrode.
$\text{Current, I}=9.65A$
$\text{Time, t}=100s$
Platinum electrode is an inert electrode. Thus, it does not involve in cell reaction. During electrolysis, $C{u}^{2+}$ is reduced at cathode because its reduction potential is higher than $H^{+}$. Hence, copper is produced at cathode. Thus, $C{u}^{2+}$ concentration in solution decreases. Hence, the blue colour intensity of solution decreases during electrolysis.
Hence, statement (a) is correct.

When copper electrode is used,
Cathode Reaction : $C{u}^{2+}\left(aq\right)+2e^{-}\to Cu\left(s\right)$
Anode Reaction : $Cu\left(s\right)\to C{u}^{2+}\left(aq\right)+2e^{-}$
Thus, the concentration of $C{u}^{2+}$ ions in solution does not change. As a result the intensity of $C{u}^{2+}$ in the solution does not change and blue colour remains constant.