chemistry
posted by Amandeep on .
What am I doing wrong?
If a current of 54 A flows into a cell for 45 minutes 30 s, determine the mass of chronium deposited.
My answer:
54 x 2730 s = 147420
147430/96485
= 1.52 mols
m = n x M
=1.52 x 52
= 79.5

I get 1.528 which would round to 1.53 but it won't make that much difference. I think your problem is the molar mass of Cr. 1 F (96,485 coulombs) will deposit 1 equivalent of Cr and 1 eq is molar mas of 52 divided by change in number of electrons. The problem isn't really specific about the nature of the Cr in solution (or perhaps you just didn't include it in your post); however, most electroplated Cr, I think, comes from Cr^+3 in solution. So the change in electrons will be 3 and 06,485 coulombs will deposit 52/3 = ?? grams Cr.

Will this help?
A car bumper is plated with chronium using chronium(III)ions in solution. If a current of 54 A flows into a cell for 45 minutes 30 s, determine the mass of chronium deposited. 
Yes. It is Cr^+3 in solution and the half cell is Cr^+3 + 3e ==> Cr.
So the equivalent weight is what I posted in my first response of 52/3 or a little over 17 g for 96,485 coulombs. I get something like 26 grams but that's an estimate.