Question

A current liberates $0.50g$ of hydrogen in $2$ hours. The weight of copper(At. wt. $=63.5$) deposited at the same time by the same current through copper sulphate solution is:

• A. $63.5g$
• B. $31.8g$
• C. $15.9g$
• D. $15.5g$

Answer 1

Answer: (C)

$15.9g$

$2H^{+}+2e^{-}\to H_2$

Mole ratio of hydrogen $=\frac{\text{moles of hydrogen produced in the half reaction}}{\text{moles of electrons required in the half reaction}}$
Mole ratio of hydrogen $=\frac{\text{1}}{\text{2}}$
$C{u}^{2+}+2e^{-}\to Cu$

Mole ratio of Cu $=\frac{\text{moles of Cu produced in the half reaction}}{\text{moles of electrons required in the half reaction}}$
Mole ratio of hydrogen $=\frac{\text{1}}{\text{2}}$
$\frac{\text{Moles of hydrogen produced}}{\text{moles of copper produced}}=\frac{\text{mole ratio of hydrogen half reaction}}{\text{mole ratio of copper half reaction}}$
$\frac{\text{0.50/2}}{\text{moles of copper produced}}=\frac{\text{1/2}}{\text{1/2}}$
$\text{moles of copper produced}=0.25$

$\text{mass of copper produced}=0.25\times 63.5=15.9$ g.