What is the difference between the two strong acids, nitric and hydrochloric acid, when
they behave as the oxidised forms in a reduction half-equation?
To determine the difference between the two strong acids, nitric (HNO3) and hydrochloric acid (HCl), when they behave as the oxidized forms in a reduction half-equation, we need to understand their chemical properties and oxidation states.
In a reduction half-equation, the substance being reduced is the one that gains electrons or decreases its oxidation state, while the substance being oxidized is the one that loses electrons or increases its oxidation state.
Let's start by looking at the chemical formulas and oxidation states of nitric and hydrochloric acid:
- Nitric acid (HNO3): In nitric acid, the nitrogen atom is in its highest possible oxidation state, which is +5. The oxidation state of hydrogen in all compounds is +1, and oxygen is usually -2. Therefore, each oxygen atom contributes -6 to the oxidation state. By using these rules, we can calculate that the oxidation state of nitrogen in nitric acid is +5.
- Hydrochloric acid (HCl): In hydrochloric acid, hydrogen has an oxidation state of +1, as it usually does. Chlorine, as a halogen, has an oxidation state of -1 in most compounds, including hydrochloric acid. Therefore, the oxidation state of chlorine in hydrochloric acid is -1.
From this information, we can see that the difference in behavior as the oxidized forms in a reduction half-equation lies in their oxidation states:
- In the reduction half-equation for nitric acid, the nitrogen atom is reduced from an oxidation state of +5 to a lower oxidation state, meaning it gains electrons.
- In the reduction half-equation for hydrochloric acid, the chlorine atom is reduced from an oxidation state of -1 to a lower oxidation state, indicating the gain of electrons.
To summarize, the key difference when nitric acid and hydrochloric acid behave as the oxidized forms in a reduction half-equation lies in the change of oxidation states of their constituent atoms. Nitric acid involves the reduction of nitrogen from +5 to a lower state, while hydrochloric acid involves the reduction of chlorine from -1 to a lower state.