Question

When $10mL$ of an aqueous solution of $F{e}^{2+}$ ions was titrated in the presence of dil $H_{2}S{O}_4$ using diphenylamine indicator, $15mL\text{of}$ $0.02M$ solution of $K_{2}C{r}_2{O}_7$ was required to get the end point. The molarity of the solution containing $F{e}^{2+}$ ions is $x\times {10}^{-2}M$. The value of $x$ is ___. (Nearest integer)

Answer 1

The reaction involved in the given titration is,
$F{e}^{2+}+C{r}_2{O}_7^{2-}\to 6F{e}^{3+}+2C{r}^{3+}$
Balancing the above equation,
$6F{e}^{2+}+C{r}_2{O}_7^{2-}+14H^{+}\to F{e}^{3+}+C{r}^{3+}+7H_{2}O$

$\text{milli~equivalents~of~}F{e}^{2+}=\text{milli-equivalents of~}{K}_{2}C{r}_2{O}_7$

$M\times 10\times 1=0.02\times 15\times 6$

$M=0.18=18\times {10}^{-2}M$