Complete Solutions and Summary of Redox Reactions – NCERT Class 11, Chemistry, Chapter 7 – Summary, Questions, Answers, Extra Questions
Summary of oxidation and reduction concepts, redox reaction definitions, oxidation numbers, types of redox reactions (combination, decomposition, displacement, disproportionation), electron-transfer methods, balancing redox reactions (oxidation number, half equation method), electrode processes, and practical applications.
Updated: 8 months ago
Redox Reactions
Chapter 7: Chemistry - Ultimate Study Guide | NCERT Class 11 Notes, Questions, Examples & Quiz 2025
Full Chapter Summary & Detailed Notes - Redox Reactions Class 11 NCERT
Overview & Key Concepts
- Chapter Goal: Explains redox as oxidation-reduction simultaneous; classical O/H add/rem, electron transfer, oxidation number (ON) rules, Stock notation, types (comb, decomp, displ, dispro), balancing (ON/half-reac methods), electrode processes. Exam Focus: Identify oxid/red, calc ON, balance eqs, classify reac, exceptions. 2025 Updates: Green chem redox; apps batteries/fuel cells. Fun Fact: Redox in breathalyzers; corrosion costs billions. Core Idea: Redox electron shift; oxid agent reduced, red agent oxidized. Real-World: Photosynthesis/respiration, metallurgy, bleaching. Ties: Builds on Ch.1 reac; leads to Ch.8 electrochem.
- Wider Scope: Basis electrochem; apps in env (water treat), pharma (antioxidants).
7.1 Classical Idea of Redox Reactions – Oxidation and Reduction Reactions
Originally oxid: add O; e.g., 2Mg+O2→2MgO; S+O2→SO2; CH4+2O2→CO2+2H2O. Extended: rem H; 2H2S+O2→2S+2H2O. Further: add electroneg elem (F,Cl,S); Mg+F2→MgF2; rem electropos (K); 2K4[Fe(CN)6]+H2O2→2K3[Fe(CN)6]+2KOH. Red: rem O; 2HgO→2Hg+O2; add H; CH2=CH2+H2→CH3-CH3; rem electroneg (Cl); 2FeCl3+H2→2FeCl2+2HCl; add electropos (Hg); 2HgCl2+SnCl2→Hg2Cl2+SnCl4. Redox simultaneous; term from red(uction)-ox(idation). Depth: Electroneg drives. Real-Life: Combustion fuels. Exam Tip: Identify oxid/red species. Extended: Bio redox NAD+. Graphs: None. Pitfalls: All O reac redox? No some not. Applications: Pharma synthesis. Interlinks: ON concept. Advanced: Free rad. Historical: Lavoisier O. NCERT: Prob7.1 H2S+Cl2 S ox Cl red; Fe3O4+Al Al ox Fe red; Na+H2 Na ox H red.
- Examples: Rust Fe ox O red.
- Point: Oxid add O/electroneg rem H/electropos; opp red.
Extended Discussion: Always paired. Errors: Isolated oxid? No. Scope: All chem areas. Principles: Conservation charge. Real: Batteries. Additional: Env O3 hole. Depth: Mech electron. Interlinks: Electron trans. Advanced: Concerted mech. Symbols: Ox ag, red ag.
7.2 Redox Reactions in Terms of Electron Transfer Reactions
Redox: loss/gain e; e.g., 2Na+Cl2→2NaCl as 2Na→2Na++2e-; Cl2+2e-→2Cl-. Half-reac: oxid loss e, red gain e. Oxid ag accept e (reduced); red ag donate e (oxidized). Prob7.2: 2Na+H2→2NaH as oxid Na red H. Depth: Ionic view. Real-Life: Galvanic cells. Exam Tip: Split reac. Extended: Comp e trans series. Graphs: Fig7.1 Zn Cu. Pitfalls: Covalent full trans? Assum. Applications: Corrosion prev. Interlinks: ON shift. Advanced: Marcus theory. Historical: Faraday. NCERT: Zn+Cu2+→Zn2++Cu; Zn oxid Cu red; eq favors prod. Cu+Ag+→Cu2++Ag favors prod; Co+Ni2+ moderate eq.
- Examples: H2+O2→H2O as H0 to +1 O0 to -2.
- Point: Electron loss oxid, gain red.
Extended: Activity series Zn>Cu>Ag. Errors: Reverse? No thermodyn. Scope: Electrodes. Principles: e trans. Real: Electroplating. Additional: H2S test ZnS. Depth: Eq conc. Interlinks: Cells XII. Advanced: Potentials. Symbols: Half-reac arrows.
7.2.1 Competitive Electron Transfer Reactions
Zn in Cu(NO3)2: Zn+Cu2+→Zn2++Cu; blue fades red Cu dep; ZnS white confirm. Eq favors prod. Cu in ZnSO4: no reac. Cu in AgNO3: Cu+2Ag+→Cu2++2Ag; blue forms. Eq favors prod. Co in NiSO4: moderate eq both ions. Depth: e release tendency Zn>Cu>Ag>Ni~Co. Real-Life: Displacement extrac. Exam Tip: Predict reac. Extended: Build series. Graphs: Fig7.2 Cu Ag. Pitfalls: All displ? No strength. Applications: Galvanic. Interlinks: Electro series. Advanced: Nernst. Historical: Volta. NCERT: Comp reminds acid proton comp.
- Examples: No Cu2+ from ZnSO4.
- Point: Stronger red displ weaker.
Extended: CuS black test fail. Errors: Eq reverse? No. Scope: Cells. Principles: Spont. Real: Coin metals. Additional: H2S alk. Depth: Ksp low. Interlinks: Solub. Advanced: Overpot. Symbols: Aq ions.
7.3 Oxidation Number
ON: charge assum full e trans more electroneg; rules: elem 0; mono ion charge; O -2 (perox -1 super -0.5 OF2 +2); H +1 (hydride -1); F -1 other hal -1/pos oxo; sum 0 comp/charge ion. Highest ON group num (1-2) or group-10 (others). Stock: Roman after metal; Au(I)Cl Au(III)Cl3. ON def oxid inc ON, red dec; oxid ag inc ON elem, red ag dec. Prob7.3: HAu(III)Cl4 Tl2(I)O Fe(II)O Fe2(III)O3 Cu(I)I Cu(II)O Mn(II)O Mn(IV)O2. Prob7.4: 2Cu2O+Cu2S→6Cu+SO2 Cu red +1 to 0 S ox -2 to +4. Depth: Avg multi atoms. Real-Life: Bleach Cl +1. Exam Tip: Calc ON. Extended: Trans vary ON. Graphs: Period inc ON. Pitfalls: Not real charge. Applications: Balance. Interlinks: Redox def. Advanced: Formal charge diff. Historical: Stock. NCERT: Covalent assum trans.
- Examples: CO2 C+4 O-2.
- Point: Book-keep e shift.
Extended: Na2S2O3 S avg +2. Errors: Pos nonmetal? Yes oxo. Scope: All comp. Principles: Electroneg. Real: Titration. Additional: Al +3 always. Depth: Rules priority. Interlinks: Types. Advanced: Ambiguous cases. Symbols: Roman ON.
Types of Redox Reactions
Comb: elem/comp +O/other; 2Mg+O2→2MgO. Decomp: rev; 2HgO→2Hg+O2. Displ: stronger displ; Zn+CuSO4→ZnSO4+Cu. Dispro: same elem oxid red; 2H2O2→2H2O+O2 Cl2+2OH-→Cl-+OCl-+H2O. Depth: Dispro auto-redox. Real-Life: Halo water treat dispro. Exam Tip: Classify. Extended: Metal/nonmetal displ. Graphs: None. Pitfalls: All decomp redox? No thermal. Applications: Pyro. Interlinks: Balance. Advanced: Cannizzaro dispro. Historical: Priestley O2 decomp. NCERT: Ex comb 2H2S+O2, decomp 2H2O→2H2+O2, displ Fe+CuSO4, dispro 3MnO42-→2MnO4-+MnO2.
- Examples: Photosyn comb.
- Point: Class based change.
Extended: Intermolec/intramolec. Errors: Neutral redox? Yes. Scope: Org. Principles: ON change. Real: Fireworks. Additional: Combus subset comb. Depth: Mech. Interlinks: ON method. Advanced: Radical chain. Symbols: Arrows types.
Balancing Redox Equations
ON method: assign ON, id change, balance atoms, e loss=gain mult, add coeff, check. Half-reac: split oxid red, balance atoms exc H O, H2O/H+ bal O H, e bal charge, add. Acid: H+, base: OH-. Depth: Ion-e eq. Real-Life: Titration KMnO4. Exam Tip: Step-by-step. Extended: Dispro same species. Graphs: None. Pitfalls: Forget H2O. Applications: Stoich. Interlinks: Electrode. Advanced: Complex media. Historical: None spec. NCERT: Ex Cr2O72-+SO2 acid; MnO4-+Fe2+.
- Examples: I2+NaOH dispro.
- Point: Conserve mass charge e.
Extended: Water autoion. Errors: Unbal charge? Check. Scope: All media. Principles: Eq. Real: Waste treat. Additional: Spec ions. Depth: Steps detail. Interlinks: Redox titr. Advanced: Nernst bal. Symbols: → eq.
Redox Reactions as the Basis for Titrations and Electrode Processes
Titr: redox indicators, KMnO4 self. Electrode: oxid anode loss e, red cathode gain; cells spont/nonspont. Depth: Galvanic/electrolytic. Real-Life: Batteries. Exam Tip: Id anode cathode. Extended: Dispro Cl2. Graphs: Fig electrode. Pitfalls: Sign conv. Applications: Fuel cells. Interlinks: XII electro. Advanced: Overpot. Historical: Volta. NCERT: Link cells.
- Examples: Daniell cell.
- Point: Redox gen elec.
Extended: Corrosion elec. Errors: All redox elec? Pot. Scope: Bioelec. Principles: e flow. Real: ECG. Additional: pH dep. Depth: Half-cell. Interlinks: Balance. Advanced: Butler-Volmer. Symbols: || salt bridge.
Summary
- Redox oxid-red simultaneous; classical O/H, e trans, ON inc/dec; types 4; balance 2 methods; electrode basis cells.
Why This Guide Stands Out
Complete: All subtopics (8+), examples solved (10+), Q&A exam-style, 30 numericals. Chem-focused with eqs/tables. Free for 2025.
Key Themes & Tips
- Simultaneous: Always paired.
- ON: Track change.
- Tip: Id ag by ON; balance e loss=gain; classify types; practice eqs; remember rules.
Exam Case Studies
Balance KMnO4; id dispro; calc ON trans.
Project & Group Ideas
- Demo displ: Cu Zn.
- Battery model: Lemon cell.
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