Question

Chromium plating is done using a dichromate solution. How long would it take to plate 1.0x10-2mm thick onto a car bumper with surface area 0.25m^2 in a 25.0 Amp electrolytic cell? (density of chromium is 7.19g/cm^3)

Cr2O7^2- + 14H^+ ==> 2Cr(s) + 12e + 7H2O
The 0.25m^2 is 25 cm x 25 cm x 1.0E-4 cm thick for volume of 0.625 cc but you should confirm that.
mass Cr = 7.19 x 0.625 = estimated 4.5 g.

96,485 coulombs will plate one (1) equivalent weight of Cr which is 52/6 g Cr or about 8.7 g but you should be more accurate. (2 Cr for 12e makes 1 Cr for 6e.)
96,485 x (8.7/4.5) = ? coulombs.
amperes x seconds = coulombs. Substitute and solve for time.

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