Question

Balance the following equation.

$HI+HN{O}_3\to I_2+NO+H_{2}O$

• A. $6HI+2HN{O}_3\to 3I_2+2NO+4H_{2}O$
• B. $6HI+4HN{O}_3\to 3I_2+2NO+H_{2}O$
• C. $3HI+2HN{O}_3\to 2I_2+2NO+4H_{2}O$
• D. None of these

Answer 1

The correct option is A $6HI+2HN{O}_3\to 3I_2+2NO+4H_{2}O$

The unbalanced redox equation is as follows:
$HI+HN{O}_3\to I_2+NO+H_{2}O$

Balance all atoms other than H and O.
$2HI+HN{O}_3\to I_2+NO+H_{2}O$

The oxidation number of Iodine changes from -1 to 0. The change in the oxidation number of one I atom is 1. For 2 I atoms, the total change in the oxidation number is 2.
The oxidation number of N changes from +5 to +2. The change in the oxidation number of one N atom is 3.

The increase in the oxidation number is balanced with decrease in the oxidation number by multiplying $HI$ and $I_2$ with 3 and by multiplying $HN{O}_3$ and $NO$ with 2.
$6HI+2HN{O}_3\to 3I_2+2NO+H_{2}O$

O atoms are balanced on adding 3 water molecules on RHS..
$6HI+2HN{O}_3\to 3I_2+2NO+4H_{2}O$
Hydrogen atoms are balanced. This is the balanced chemical equation.