Question detail
What is the balanced half-equation for the reduction of permanganate ions (MnO4-) in acidic solution?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Oxidation, reduction and redox equations
Question
- A. MnO4- + 8H+ + 5e- → Mn2+ + 4H2O
- B. MnO4- + 4H2O + 8e- → Mn2+ + 8OH-
- C. MnO4- + 3e- + 6H+ → MnO2 + 3H2O
- D. MnO4- + 2e- + 4H+ → MnO2 + 2H2O
Answer
MnO4- + 8H+ + 5e- → Mn2+ + 4H2O
Explanation
The correct option is MnO4- + 8H+ + 5e- → Mn2+ + 4H2O. MnO4- + 8H+ + 5e- → Mn2+ + 4H2O is the best answer because it directly supports the AQA A-Level Chemistry objective to balance atoms and charges in redox equations. This reasoning is anchored to Redox equations in Oxidation, reduction and redox equations, and it separates redox equation from similar A-Level ideas rather than relying on a vague recall statement. Other options are weaker if they use the wrong evidence, calculation, mechanism, observation, unit, or conclusion for this subtopic.
Common mistake
Balancing Redox Equations Mistake
Students often forget to balance both the number of atoms and the charges in redox equations, leading to incorrect final equations.
To balance a redox equation, first separate the oxidation and reduction half-equations. Ensure that both the number of atoms and the total charge are equal on both sides. For example, in the half-equation for the reduction of MnO4- to Mn2+, balance the manganese and oxygen atoms, then balance the charges by adding electrons. This ensures the final redox equation is accurate.
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