Question

Purification of chromium can be achieved by electrorefining chromium from an impure chromium anode onto a pure chromium cathode in an electrolytic cell. How many hours will it take to plate 13.5 kg of chromium onto the cathode if the current passed through the cell is held constant at 30.0 A ? Assume the chromium in the electrolytic solution is present as Cr 3 +.

Answer 1

Answer:

696 h

Explanation:

Let's consider the reduction of Cr³⁺.

Cr³⁺(aq) + 3e⁻ → Cr(s)

We can establish the following relations.

• The molar mass of Cr is 52.0 g/mol.
• 1 mol of Cr is deposited when 3 moles of e⁻ circulate.
• 1 mole of e⁻ has a charge of 96468 c (Faraday's constant).
• 1 A = 1 c/s
• 1 h = 3600 s

How many hours will it take to plate 13.5 kg of chromium onto the cathode if the current passed through the cell is held constant at 30.0 A?

$13.5 \times 10^{3} gCr.\frac{1molCr}{52.0gCr} .\frac{3mol/e^{-} }{1molCr} .\frac{96468c}{1mol/e^{-}} .\frac{1s}{30.0c} .\frac{1h}{3600s} =696 h$