When Cr+3 + 3e- → Cr(s)
So according to the charge formula:
charge Q = I * t
when we have I (the current) = 7.4 a
and t (the time in seconds) = 1.85d * 24h * 60 min*60sec= 159840 sec
by substitution:
Q = 7.4 a * 159840 sec = 1182816 C
now to get the mass we have to use Faraday constant which is:
F = e NA
= 1.602 x 10^-19 * 6.022 x 10^23
= 96485 C mol^-1
when e is the electron charge & NA Avogadro's number for the charge in on mol
and as we can see from the equation Cu3+ reacts with 3 electrons so,
the mass of Cr(s) = Q* (1mole-/F) * (1molCr / 3 mol e-)
= 1182816 * (1/96485) * (1/3)
= 4.1 g
