Electrochemistry - Result Question 90
38. Chromium metal can be plated out from an acidic solution containing $CrO _3$ according to the following equation.
$ CrO _3(a q)+6 H^{+}(a q)+6 e^{-} \longrightarrow Cr(s)+3 H _2 O $
Calculate (i) How many grams of chromium will be plated out by $24,000$ $ C$ and (ii) How long will it take to plate out $1.5$ $ g$ of chromium by using $12.5$ $A$ current?
(1993, 2M)
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Solution:
- Molar mass of $Cr=52 g$
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=2.15$ $ g $
(ii) Number of gram equivalent of $Cr=\frac{1.5}{52} \times 6=\frac{9}{52}$
$\Rightarrow$ Coulombs required for $1.5 $ $g$ $ Cr=\frac{9}{52} \times 96500=I t$
$ \Rightarrow t=\frac{9 \times 96500}{52 \times 12.5} s=22.27$ $ min $
BETA
