Question

Dissolved $O_2$ in water is determined by using a redox reaction as follows:
$2M{n}^{2+}\left(aq\right)+4O\stackrel{⊝}{H}\left(aq\right)+O_2\left(g\right)\to 2Mn{O}_2\left(s\right)+2H_{2}O\left(l\right)$
How many equivalents of $O_2$ will be required to react with $1$ mol of $M{n}^{2+}$?

• A. $1$
• B. $2$
• C. $3$
• D. $4$

Answer 1

Answer: (B)

$2$

The redox changes are as follows:

$M{n}^{2+}\to Mn{O}_2+2e^{-}$
$4e^{-}+O_2\to 2H_{2}O$
$1$ equivalent of $M{n}^{2+}=1$ equivalent of $O_2$
$(n=2)$ $(n=4)$
$⟹\frac{1}{2}$ mol $=1$ equivalent
$2$ mol $M{n}^{2+}=4$ equivalents of $O_2$

Hence, $4$ equivalents of $O_2$ will be required to react with $1$ mol of $M{n}^{2+}$.