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 $1.5 g Cr=\frac{9}{52} \times 96500=I t$
$$ \Rightarrow \quad t=\frac{9 \times 96500}{52 \times 12.5} s=22.27 min $$
