Question

When the ion ${Cr}_2{O}_7^{2-}$ acts as an oxidant in acidic aqueous solution the ion ${Cr}^{3+}$ is formed. How many moles of ${Sn}^{2+}$ would be oxidised to ${Sn}^{4+}$ by one mole of ${Cr}_2{O}_7^{2-}$ ions?

• A. $\frac{2}{3}$
• B. $\frac{3}{2}$
• C. $2$
• D. $3$

Answer 1

Answer: (D)

$3$

$7H^{+}+S{n}^{2+}+C{r}_2{O}_7^{2-}⟶2C{r}^{3+}+S{n}^{4+}+7H_{2}O$

$n$-factor of $Sn$ is $4-2=2$

Change in oxidation state of $Cr$ is $2(6-3)=2\left(3\right)=6$ (n-factor)

In any reaction moles $\times n$-factor must be same on both sides

$\Rightarrow 1\times 6=n$ moles $\times 2$

$\Rightarrow 6=n\times 2$

$\Rightarrow n=3$

$\therefore 3$ moles of $S{n}^{2+}$ can be oxidized by $1$ mole of $C{r}_2{O}_7^{2-}$ .