Some species in aqueous solutions are neither oxidised or reduced. These include water molecules H2O and hydrogen ions H+ in acidic solutions and hydroxide ions OH- in alkaline solutions. They should be balanced separately.For example:unbalanced MnO4- in acidic solution where MnO4- is reduced to Mn2+ MnO4- + H+→ Mn2+ Balance the oxygens. MnO4- + H+→ Mn2+ + 4H2O Balance the hydrogens. MnO4- + 8H+→ Mn2+ + 4H2O Balance the charges with electrons. MnO4- + 8H+ + 5e-→ Mn2+ + 4H2O The Mn has been reduced from oxidation state of +7 to +2 so 5 electrons are needed.
Redox Reactions in Aqueous Solutions
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Specification: AQA Chemistry (7404), AS-level, 3.1.7 Oxidation, reduction and redox equations. Topic: Oxidation and Reduction.
Key terms in this lesson
- Oxidation
- The addition of oxygen, the removal of hydrogen, the loss of electrons, or an increase in oxidation number.
- Oxidation number
- A number that represents the number of electrons an atom has lost or gained, or would do if the compound were fully ionic.
More in Oxidation and Reduction
- Rules for Oxidation State
- Working Out Oxidation States
- Superoxide
- Redox Equations
- Thermite Reaction
- Half Equations from Ionic Equations
- Exam Style Question - 1
- Exam Style Question - 2
All 15 lessons in Oxidation and Reduction · All AQA AS-level Chemistry topics