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Q.
An acidic solution of $Cu^{2+}$ containing $0.4\, g$ of $Cu^{2+}$ ions is electrolysed until all the copper is deposited. What is the volume of oxygen evolved at $NTP$ ?
Electrochemistry
Solution:
Moles of $Cu =\frac{0.4}{63.5}=6.3 \times 10^{-3} mol$
Faraday used $=2 \times 6.3 \times 10^{-3}=12.6 \times 10^{-3} mol$
Now for oxygen,
$
\begin{array}{l}
2 H _{2} O \longrightarrow O _{2}+4 H ^{+}+4 e ^{-} \\
\text {Hence, } 4 mol e ^{-} \longrightarrow 22400 cm ^{3} \text { of } O _{2} . \\
12.6 \times 10^{-3} \longrightarrow \frac{22400}{2} \times 12.6 \times 10^{-3} cm ^{3} \text { of } O _{2} \\
=141 cm ^{3}
\end{array}
$