s/mod/ibis/view.php?id 4206223 11/30/2017 1155 PM 63/1011/30/2017 01:48 PM uesti

Question

s/mod/ibis/view.php?id 4206223 11/30/2017 1155 PM 63/1011/30/2017 01:48 PM uestion 22 of 22 Sapling Learning Ma 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 31.0 A? Assume the chromium in the electrolytic solution is present as Cr Number Hint O Previous Check Answer eE

Explanation / Answer

you have 13.5 kg of chromiu, or 13500 grams of chromium , molar mass Cr is 52 g/gmol

moles of Chromium are = mass / molar mass

moles = 13500 / 52 = 259.61 moles

The reaction that takes place is

Cr+3 + 3e- ===== Cr

so for every mole of Cr+3 you need 3 moles of Electrons

moles of electrons are 259.61 * 3 = 778.83 moles of e

multiply this by the faraday constant = 778.83 * 96500 = 75,157,095 Coulombs

remember that Intensity = Charge / Time

time = Charge / intensity, intensity is amperes, we have 31 Amperes from statement

time = 75,157,095 / 31 = 2, 424, 422.42 secs, this is in seconds

if you want hours you have to remember that 1 hour is equal to 3600 secs

time = 2424422.419 / 3600 = 673.45 hours

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