What is the change in the oxidation number of manganese in the following? KMnO4 → MnSO4 Increase by four units. Increase by three units. Decrease by four units. Decrease by five units
The Correct Answer and Explanation is:
The correct answer is Decrease by five units.
Explanation:
In the reaction KMnO4 → MnSO4, we need to track the change in the oxidation number of manganese (Mn) as it goes from one compound to another.
- Oxidation state of Mn in KMnO4:
- Potassium permanganate (KMnO4) consists of the potassium ion (K⁺), the permanganate ion (MnO₄⁻), and the overall charge is neutral.
- In the permanganate ion, the sum of the oxidation states of all atoms is -1 (since it is an anion).
- Oxygen (O) typically has an oxidation state of -2. Since there are four oxygen atoms, the total oxidation state for oxygen is 4 × (-2) = -8.
- To balance the -8 from oxygen, the oxidation state of manganese (Mn) must be +7 (because +7 + (-8) = -1). Therefore, the oxidation state of Mn in KMnO4 is +7.
- Oxidation state of Mn in MnSO4:
- In manganese sulfate (MnSO4), sulfate (SO₄²⁻) is the anion, and it carries a charge of -2. The compound is neutral, so the oxidation state of manganese must be +2 to balance the -2 charge from sulfate.
- Therefore, the oxidation state of Mn in MnSO4 is +2.
- Change in the oxidation number of Mn:
- The oxidation number of manganese changes from +7 in KMnO4 to +2 in MnSO4.
- The change is calculated as: +2 (Mn in MnSO4) – (+7) (Mn in KMnO4) = -5.
- This indicates a decrease in the oxidation state by 5 units.
Thus, the oxidation state of manganese decreases by five units in the given reaction, from +7 to +2. This is a reduction, which means manganese has gained electrons in the process.
