Question

An acidic solution of dichromate is electrolyzed for 8 minutes using 2A current . As per the following equation $Cr2O_7^{2-}+14H^{+}+6e^{-}\to 2C{r}^{3+}+7H_{2}O$
The amount of $C{r}^{3+}$ obtained was 0.104 g . The efficiency of the process (in %) is _______(nearest integer)(Take : F=960000 C , Atomic mass of chromium = 52 )

• A. 60.0
• B. 60.00
• C. 60

Answer 1

Answer: (A), (B), (C)

Charge (q) = It = 2 x 8 x 60 = 960 C
I is current
t is time
$\Rightarrow \frac{960}{96000}=0.01F$

$C{r}_2{O}_7^{2-}+14H^{+}+6e^{-}\to 2C{r}^{3+}+7H_{2}O$

Thus, 1 F is used to produce $\frac{1}{3}$ mole of $C{r}^{3+}$
Hence, $0.01F\text{gives}\frac{1}{3}\times 0.01molC{r}^{3+}$

Theoritical mass of $C{r}^{3+}=\frac{1}{3}\times 0.01\times 52=0.173g$

So , efficiency $=\frac{W_{actual}}{W_{Theoretial}}\times 100=\frac{0.104}{0.173}\times 100=60\%$