Question

What would be the value of stoichiometric coefficients of $Mg$ and $V{O}_4^{3-}$ respectively, in the balanced net ionic equation for the given redox reaction in acidic medium:
$Mg\left(s\right)+V{O}_4^{3-}\left(aq\right)\to M{g}^{2+}\left(aq\right)+V^{2+}\left(aq\right)$

• A. 3,2
• B. 8, 16
• C. 1, 1
• D. 5,10

Answer 1

The correct option is A 3,2


$\stackrel{0}{M}g\left(s\right)+\stackrel{+5}{V}{O}_4^{3-}\left(aq\right)\to \stackrel{+2}{M}{g}^{2+}\left(aq\right)+\stackrel{+2}{V}{}^{2+}\left(aq\right)$

Oxidation:

$\stackrel{0}{M}g\left(s\right)\to \stackrel{+2}{M}{g}^{2+}\left(aq\right)$
$n_f=(|2-0|)\times 1=2$

Reduction:
$\stackrel{+5}{V}{O}_4^{3-}\left(aq\right)\to {\stackrel{+2}{V}}^{2+}\left(aq\right)$
$n_f=(|2-5|\times 1=3$

$V{O}_4^{3-}$ is oxidising agent
$Mg$ is reducing agent.

Cross mutiply the oxidising and reducing agents with ratio of n-factors.
$3Mg\left(s\right)+2V{O}_4^{3-}\left(aq\right)\to M{g}^{2+}\left(aq\right)+V^{2+}\left(aq\right)$

Balancing all species except $O$ and $H$
$3Mg\left(s\right)+2V{O}_4^{3-}\left(aq\right)\to 3M{g}^{2+}\left(aq\right)+2V^{2+}\left(aq\right)$

Balance oxygen atoms by adding $H_{2}O$.
$3Mg\left(s\right)+2V{O}_4^{3-}\left(aq\right)\to 3M{g}^{2+}\left(aq\right)+2V^{2+}\left(aq\right)+8H_{2}O\left(l\right)$

Balance hydrogen.
$3Mg\left(s\right)+2V{O}_4^{3-}\left(aq\right)+16H^{+}\left(aq\right)\to 3M{g}^{2+}\left(aq\right)+2V^{2+}\left(aq\right)+8H_{2}O\left(l\right)$

balance charge
charge in reactant side = -6+16=+10
charge in product side = +10
so the balanced equation is $3Mg\left(s\right)+2V{O}_4^{3-}\left(aq\right)+16H^{+}\left(aq\right)\to 3M{g}^{2+}\left(aq\right)+2V^{2+}\left(aq\right)+8H_{2}O\left(l\right)$
The coefficients of $Mg$ and $V{O}_4^{3-}$ respectively are 3 and 2.