Final answer:
The half-reaction NO₂⁻ → NO is balanced by adding water (H₂O) to the right side to balance oxygen and then adding hydrogen ions (H⁺) to the left side to balance hydrogen. Finally, electrons (e⁻) are added to the right side to balance the charges, indicating it's a reduction process since electrons are gained.
Step-by-step explanation:
To balance the half-reaction NO₂⁻ → NO in an acidic solution, we follow a series of steps. First, we balance the elements other than hydrogen and oxygen. In our case, both sides have one nitrogen atom, so no further balancing of nitrogen is necessary.
Next, we balance the oxygen atoms. The left side has two oxygen atoms while the right only has one, so we add one water molecule (H₂O) to the right side to balance the oxygen atoms.
After balancing oxygen with water, we need to balance the hydrogen atoms using hydrogen ions (H⁺). Since we added one H₂O molecule (containing two hydrogen atoms) on the right, we now add two H⁺ ions to the left side.
The last step is to balance the charges by adding electrons. The NO₂⁻ ion has a charge of -1, while the right side after adding water and hydrogen ions has a charge of +1 (+2 from H⁺ and -1 from NO), so we must add two electrons to the right side to balance the charges. The balanced half-reaction then becomes:
- NO₂⁻ + 2H⁺ + 1e⁻ → NO + H₂O
This is a reduction process because the nitrogen atom in NO₂⁻ gains electrons to form NO.