Question

The balanced equation in acidic medium is:
$N_2{O}_4+{BrO}_3^{-}\underset{H_{2}O}{\overset{H+}{\to }}{NO}_3^{-}+B{r}^{-}$

• A. $3N_2{O}_4+{BrO}_3^{-}+3H_{2}O\to 6{NO}_3^{-}+B{r}^{-}+6H^{+}$
• B. $3N_2{O}_4+5{BrO}_3^{-}+3H_{2}O\to 6{NO}_3^{-}+4B{r}^{-}+6H^{+}$
• C. $3N_2{O}_4+3{BrO}_3^{-}+3H_{2}O\to 6{NO}_3^{-}+B{r}^{-}+6H^{+}$
• D. None of these

Answer 1

Answer: (A)

$3N_2{O}_4+{BrO}_3^{-}+3H_{2}O\to 6{NO}_3^{-}+B{r}^{-}+6H^{+}$

The unbalanced redox equation is as follows:
$N_2{O}_4+{BrO}_3^{-}\underset{H_{2}O}{\overset{H+}{\to }}{NO}_3^{-}+B{r}^{-}$
Balance all atoms other than H and O.
$N_2{O}_4+{BrO}_3^{-}\underset{H_{2}O}{\overset{H+}{\to }}2{NO}_3^{-}+B{r}^{-}$
The oxidation number of N changes from +4 to +5. The change in the oxidation number of N is 1. Total change in the oxidation number for 2 N atoms is 2.
The oxidation number of Br changes from +5 to -1. The change in the oxidation number of Cl is 6.
The increase in the oxidation number is balanced with decrease in the oxidation number by multiplying $N_2{O}_4$ and $N{O}_3^{-}$ with 3.
$3N_2{O}_4+{BrO}_3^{-}\underset{H_{2}O}{\overset{H+}{\to }}6{NO}_3^{-}+B{r}^{-}$
O atoms are balanced by adding 3 water molecules on LHS.
$3N_2{O}_4+{BrO}_3^{-}+3H_{2}O\underset{H_{2}O}{\overset{H+}{\to }}6{NO}_3^{-}+B{r}^{-}$
Hydrogen atoms are balanced by adding 6 $H^{+}$ atoms on the RHS.
$3N_2{O}_4+{BrO}_3^{-}+3H_{2}O\underset{H_{2}O}{\overset{H+}{\to }}6{NO}_3^{-}+B{r}^{-}+6H^{+}$
This is the balanced chemical equation.