How much time should a bumper be immersed in Chromium vat?

Question

To save on production costs, most automobile bumpers are never coated with more than 300 g of chromium. Determine how much time a standard bumper should be immersed in a chromium vat. Give your answer to the nearest whole second. 



Recall from the previous question that the power supply used in commercial electroplating provides each vat with approximately 1.50 x 10³ A of current.

Answer 1

Chromium (Cr) has an atomic mass of 52 g/mol. Usually, hexavalent Cr is used in electroplating, i.e. Cr⁶⁺.

To get Cr(s) to be deposited, this means 6 mols of electrons per mol of Cr.

300 g Cr(s) x 1 mol Cr/52 g = 5.77 mols Cr(s)

5.77 mols Cr(s) x 6 mols e- / mol Cr = 34.6 mols of electrons needed

(Note: if for some reason your problem uses Cr²⁺ or Cr³⁺, the mols of electrons should be adjusted accordingly)

1 mol e- = 96,485 Coulombs

96,485 C/mol e- x 34.6 mols e- = 3,338,381 C required

1 amp = 1 coulomb/sec

1.50x10³ A = 1.50x10³ C/sec

3,338,381 C x 1 sec / 1500 C = 2226 seconds