How much electricity, in faradays, is required to produce 20 g of calcium from molten CaCl2? (Molar mass of Ca = 40 g mol−1)
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 1 F
One faraday (1 F) is the charge on one mole of electrons. In molten \( \ce{CaCl2} \), calcium ions are reduced at the cathode:
\( \displaystyle \ce{Ca^2+(l) + 2e^- -> Ca(s)} \)
Moles of Ca: \( \frac{20\,\mathrm{g}}{40\,\mathrm{g\,mol^{-1}}} \) = 0.5 mol.
Moles of electrons: 2 mol of electrons per mol of Ca, so 0.5 × 2 = 1 mol of electrons.
Charge: 1 mol of electrons = 1 F.