Question

Chromium metal can be plated out from an acidic solution containing $Cr{O}_3$ according to the following equation.
$Cr{O}_3(aq)+6H^{+}(aq)+6e^{-}⟶Cr(s)+3H_{2}O$
Calculate (i) How many grams of chromium will be plated out by $24,000C$ and (ii) How long will it take to plate out $1.5g$ of chromium by using $12.5A$ current?

Answer 1

Molar mass of $Cr=52g$
Equivalent mass of $Cr=\frac{52}{6}g$
(i) Mass of Cr deposited on passing $24000$ Coulombs
$=\frac{24000}{96500}\times \frac{52}{6}g=2.15g$
(ii) Number of gram equivalent of $Cr=\frac{1.5}{52}\times 6=\frac{9}{5\text{. }}$
$\Rightarrow$ Coulombs required for $1.5gCr=\frac{9}{52}\times 96500=It$
$\Rightarrow t=\frac{9\times 96500}{52\times 12.5}s=22.27\min$