NEET Physics: Waves – NCERT Masterclass & 100 MCQ Quiz

REDOX REACTIONS

NCERT Masterclass & NEET Study Module

1. Classical and Electronic Concepts of Redox Reactions

• Oxidation: Addition of oxygen/electronegative element, or removal of hydrogen/electropositive element. Electronically: Loss of electrons (LEO).
• Reduction: Addition of hydrogen/electropositive element, or removal of oxygen/electronegative element. Electronically: Gain of electrons (GER).
• Oxidising Agent (Oxidant): Acceptor of electrons (gets reduced).
• Reducing Agent (Reductant): Donor of electrons (gets oxidized).

2. Oxidation Number (O.N.)

Oxidation number denotes the oxidation state of an element in a compound ascertained according to a set of rules formulated on the basis that electron pair in a covalent bond belongs entirely to the more electronegative element.

🔥 NEET Exceptions & Important Rules:

• O.N. of elements in free/uncombined state is ZERO (e.g., $H_2, O_2, S_8, P_4$).
• Oxygen is usually -2. Exceptions: Peroxides like $H_2O_2$ (-1), Superoxides like $KO_2$ (-1/2), and in $OF_2$ (+2), $O_2F_2$ (+1).
• Hydrogen is usually +1. Exception: In metal hydrides like $NaH, CaH_2$ it is -1.
• Fluorine is ALWAYS -1 in all its compounds.
• Maximum Oxidation State: Cannot exceed the group number (valence electrons). E.g., Osmium ($OsO_4$) and Ruthenium ($RuO_4$) show the highest O.N. of +8.

3. Types of Redox Reactions

• Combination Reactions: $A + B \rightarrow C$ (At least one must be in elemental form).
• Decomposition Reactions: Breakdown of a compound. $2KClO_3 \rightarrow 2KCl + 3O_2$.
• Displacement Reactions: An ion/atom in a compound is replaced by an ion/atom of another element. Includes Metal displacement and Non-metal displacement.
• Disproportionation Reactions: A VERY IMPORTANT class where the SAME element is simultaneously oxidized and reduced.
  Example: $2H_2O_2^{-1} \rightarrow 2H_2O^{-2} + O_2^0$. (Oxygen goes from -1 to -2 and 0).

4. Balancing of Redox Reactions

Two methods are generally used: Oxidation Number Method and Half-Reaction (Ion-Electron) Method.
Rules for Acidic Medium: Balance O atoms by adding $H_2O$, then balance H atoms by adding $H^+$. Finally, balance charge by adding electrons ($e^-$).
Rules for Basic Medium: Balance as in acidic medium, then for every $H^+$ added, add an equal number of $OH^-$ ions to BOTH sides. $H^+$ and $OH^-$ combine to form water.

5. Redox Reactions & Electrode Processes

In an electrochemical cell (Galvanic/Voltaic Cell), spontaneous redox reactions generate electricity.

ANOX: Anode - Oxidation (Negative Pole)
RED CAT: Reduction - Cathode (Positive Pole)
$E^\ominus_{cell} = E^\ominus_{cathode} - E^\ominus_{anode}$

Electrochemical Series: A series where elements are arranged in order of their standard reduction potentials ($E^\ominus$).
Fluorine has the highest positive reduction potential (+2.87 V), making it the strongest oxidizing agent.
Lithium has the most negative reduction potential (-3.05 V), making it the strongest reducing agent.

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🚀 NEET REDOX REACTIONS MEGA QUIZ (100 MCQ)

Solve the 5 parts below to master Oxidation Numbers, Balancing, and Electrochemistry.

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