A solution of \( CuSO_4 \) is electrolyzed for 1 minute with a current of 1 ampere. Given the atomic mass of Cu as \( 63\, g\, mol^{-1} \), the mass of copper deposited at the cathode is
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (1890/F) g
By Faraday’s first law, the mass deposited is proportional to the charge passed. To deposit one mole of a metal from its ion \( \ce{M^{n+}} \), n moles of electrons, that is nF coulombs, are needed:
\( \displaystyle m = \frac{M \times Q}{nF} \)
The charge passed in 1 minute at 1 ampere:
\( \displaystyle Q = I \times t = 1\ \mathrm{A} \times 60\ \mathrm{s} = 60\ \mathrm{C} \)
At the cathode, copper is deposited from \( \ce{Cu^2+} \), which takes two electrons per atom, so n = 2:
\( \displaystyle \ce{Cu^2+ + 2e- -> Cu(s)} \)
\( \displaystyle m = \frac{63\ \mathrm{g\,mol^{-1}} \times 60\ \mathrm{C}}{2 \times F} = \frac{3780}{2F}\ \mathrm{g} = \frac{1890}{F}\ \mathrm{g} \)
So the mass of copper deposited is (1890/F) g, about 0.0196 g with F = 96487 C mol−1.