Balancing Redox Reactions

topicmedium9 MCQ

Oxidation-number and ion-electron half-reaction methods. (Chemistry › Redox Reactions, NEET UG syllabus.)

What is Balancing Redox Reactions?

The hypothetical charge an atom would have if all bonds were ionic, used to track electron transfer in redox reactions.

Key formula / rule: Oxidation Number Method (General Steps)

Apply the oxidation number method to balance redox reactions in both acidic and basic media.
Apply the ion-electron (half-reaction) method to balance redox reactions in both acidic and basic media.
Distinguish and correctly apply the rules for balancing H and O atoms in acidic versus basic conditions.
Verify that a balanced redox equation conserves both mass and charge.

Incorrectly assigning oxidation numbers to elements.

Term: Oxidation Number
Meaning: The hypothetical charge an atom would have if all bonds were ionic, used to track electron transfer in redox reactions.

Term: Redox Reaction
Meaning: A chemical reaction involving the transfer of electrons, where oxidation and reduction occur simultaneously.

Term: Oxidation
Meaning: A process involving the loss of one or more electrons by an atom, ion, or molecule, resulting in an increase in its oxidation number.

Term: Reduction
Meaning: A process involving the gain of one or more electrons by an atom, ion, or molecule, resulting in a decrease in its oxidation number.

Term: Half-Reaction
Meaning: A component of a redox reaction that shows either the oxidation or the reduction process, including the electrons transferred.

Apply the oxidation number method to balance redox reactions in both acidic and basic media.
Apply the ion-electron (half-reaction) method to balance redox reactions in both acidic and basic media.
Distinguish and correctly apply the rules for balancing H and O atoms in acidic versus basic conditions.
Verify that a balanced redox equation conserves both mass and charge.

Name: Oxidation Number Method (General Steps)
Note: This is a procedural 'formula' for balancing.
Expression: 1. Assign oxidation numbers. 2. Identify atoms undergoing oxidation and reduction. 3. Calculate total increase/decrease in O.N. 4. Equalize total O.N. change using coefficients. 5. Balance other atoms (not H, O). 6. Balance O atoms by adding H₂O. 7. Balance H atoms by adding H⁺ (acidic) or H₂O/OH⁻ (basic).

Name: Ion-Electron (Half-Reaction) Method (General Steps)
Note: This is a procedural 'formula' for balancing.
Expression: 1. Separate into oxidation and reduction half-reactions. 2. Balance atoms other than O and H. 3. Balance O atoms by adding H₂O. 4. Balance H atoms by adding H⁺ (acidic). 5. Balance charge by adding electrons (e⁻). 6. Equalize electrons in both half-reactions by multiplying. 7. Add the two half-reactions and cancel common species. 8. (For basic medium) Convert H⁺ to H₂O/OH⁻ after step 7.

Incorrectly assigning oxidation numbers to elements.
Failing to balance charge in half-reactions by adding electrons.
Incorrectly balancing H and O atoms, especially confusing acidic vs. basic medium rules.
Not equalizing the number of electrons before adding the two half-reactions.
Forgetting to cancel common species (e.g., H₂O, H⁺, OH⁻, e⁻) after combining half-reactions.

Balance the following reaction using the oxidation number method in acidic medium: P₄(s) + HNO₃(aq) → H₃PO₄(aq) + NO₂(g) + H₂O(l) What is the sum of the stoichiometric coefficients of P₄ and HNO₃ in the balanced equation…
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In the balanced redox reaction in basic medium: MnO₄⁻(aq) + Br⁻(aq) → MnO₂(s) + BrO₃⁻(aq) What is the stoichiometric coefficient for OH⁻?…
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In the reaction, 2Na(s) + Cl₂(g) → 2NaCl(s), which element undergoes oxidation?…
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