Question

An element A in a compound ABD has oxidation number $A^{n-}$. It is oxidised by $C{r}_2{O}_7^{2-}$ in acid medium. In the experiment $1.68\times 10^{-3}$ moles of $K_{2}C{r}_2{O}_7$ was used for $3.26\times 10^{-3}$ moles of ABD. The new oxidation number of A after oxidation is:

• A. $3$
• B. $3-$n
• C. n $-3$
• D. $+n$

Answer 1

Answer: (B)

Meq. of $K_{2}C{r}_2{O}_7=$ Meq. of ABD
n-factor of $K_{2}C{r}_2{O}_7$ , in acidic medium $=6$
$6\times 1.68\times 10^{-3}=x\times 3.26\times 10^{-3}$
$x=3$
$\Rightarrow$ New oxidation state of $A^{-n}$ will be = $-n+3$