Question

1200 grams of chromium from a standard Cr3+ electrolyte is electroplated onto an iron truck part with a current of 200 amps. a. Calculate the amount of time for this process to occur. b. Calculate the thickness of the electroplated chromium over the sample of iron with a surface area of 120 in2 (answer in mils).

Answer 1

Cathode (reduction): Cr3+ + 3e- ---> Cr(s)
a) Moles of Cr by converting mass of Cr produced into moles using the molar mass of Cr
= 1200 g * (1 mole of Cr/51.99 g/mol)
= 23.076 moles of Cr

Now, calculating the moles of e- required to produce the moles of Cr from the balanced half-reaction. According to the equation 3 moles of electrons will produce one mole of Cr
=23.076 mole of Cr * (3 moles of e-/1 mole of Cr) = 69.23 moles of e-  

Now, converting the moles of electrons into coulombs of charge using Faraday's constant
=69.23 moles of e-* (1 F/1 mole of e-)= 69.23 F
=69.23 F* (96485 C/1F)= 6679730.77 C

Now, calculating the time using the current and the coulombs of charge
200 Amp * t = 6679730.77 C
time, t = 33398.65 sec= 9.277 hours