Chemistry Notes – Set 11: Detailed Guide for UPSC, PCS, SSC Competitive Exams

Class 9: Basics of Elements and Compounds

Detailed Concepts:

• Elements: Pure substances with one type of atom, cannot be chemically broken down.
  • Classification:
    • Metals: Shiny, conductive (e.g., Cu, Fe), form basic oxides (e.g., MgO).
    • Non-Metals: Dull, poor conductors (e.g., C, S), form acidic oxides (e.g., CO₂).
    • Metalloids: Intermediate properties (e.g., Si, used in semiconductors).
  • Properties: Fixed melting/boiling points (e.g., Fe: 1538°C melting point), unique chemical behavior (e.g., Na reacts with water).
• Compounds: Two or more elements chemically combined in fixed ratios (e.g., H₂O, NaCl).
  • Properties: Differ from constituent elements (e.g., H₂O vs. H₂, O₂), fixed composition (e.g., H₂O: 11.11% H, 88.89% O).
  • Types:
    • Ionic: Metal + non-metal (e.g., NaCl, ionic bonds).
    • Covalent: Non-metals (e.g., CO₂, covalent bonds).
• Chemical Behavior:
  • Reactivity: Metals lose electrons (e.g., Mg → Mg²⁺), non-metals gain (e.g., Cl → Cl⁻).
  • Reactions: Form compounds via combination (e.g., 2H₂ + O₂ → 2H₂O), decomposition (e.g., 2HgO → 2Hg + O₂).
• Applications:
  • Industrial: NaCl in chemical synthesis, Si in electronics.
  • Daily Life: H₂O in hydration, CO₂ in carbonated drinks.
  • Environmental: CO₂ in photosynthesis, Fe in construction (prone to rusting).
• Mixtures vs. Compounds:
  • Mixtures: Variable composition, physically separable (e.g., air: N₂, O₂).
  • Compounds: Fixed composition, chemically bonded.
• Applications in Exams: Understanding element/compounds classification and their chemical behavior is key for objective and descriptive questions.

Formulas:

• Percentage Composition: % = (n × Atomic mass / Molecular mass) × 100 (e.g., H₂O: H = (2 × 1 / 18) × 100 = 11.11%).
• Combination: 2Mg + O₂ → 2MgO.
• Decomposition: 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂.
• Rusting: 4Fe + 3O₂ + 2xH₂O → 2Fe₂O₃·xH₂O.

Applications:

• Competitive Exams:
  • UPSC/PCS: Questions on element applications in industry (e.g., Si in chips) or environmental chemistry (e.g., CO₂ in carbon cycle).
  • SSC: Objective questions on element properties, compounds vs. mixtures, or reactions.
  • Descriptive: Explain uses of NaCl or chemical behavior of metals.
• Real-World:
  • Industry: Al in packaging, C in fuels.
  • Environment: CO₂ in greenhouse effect, O₂ in respiration.
  • Daily Life: NaCl in food, H₂O in household use.
• Exam Tips:
  • Focus on distinguishing elements, compounds, and mixtures.
  • Link to environmental science (e.g., CO₂ emissions) for mains.

Diagram (Textual Description):

• Ionic vs. Covalent Compounds: Show NaCl (ionic lattice, Na⁺ and Cl⁻ ions) vs. CO₂ (linear molecule, C=O double bonds). Label NaCl’s ionic bonds (electrostatic) and CO₂’s covalent bonds (shared electrons), highlighting different properties (e.g., NaCl: high melting point; CO₂: gas).

---

Class 10: Metals and Non-Metals

Detailed Concepts:

• Note: Revisiting Set 3’s “Metals and Non-Metals” with a focus on industrial and environmental applications to avoid redundancy, tailored for Class 10 level and exam needs.
• Metals:
  • Properties: Shiny, malleable, ductile, good conductors (e.g., Cu, Fe), form basic oxides (e.g., Na₂O).
  • Reactivity Series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Ag > Au.
    • High reactivity metals (e.g., Na) react with water (2Na + 2H₂O → 2NaOH + H₂).
    • Less reactive metals (e.g., Cu) resist corrosion.
• Non-Metals:
  • Properties: Dull, brittle, poor conductors (e.g., S, C), form acidic oxides (e.g., SO₂ → H₂SO₃).
  • Reactivity: Varies (e.g., F highly reactive, C less reactive).
• Extraction of Metals:
  • Highly Reactive (Na, K): Electrolysis (e.g., NaCl → Na + Cl₂).
  • Moderately Reactive (Zn, Fe): Reduction with C (e.g., Fe₂O₃ + 3C → 2Fe + 3CO).
  • Low Reactive (Ag, Au): Found native or cyanide leaching.
• Alloys:
  • Mixtures enhancing properties (e.g., steel: Fe + C; brass: Cu + Zn).
• Corrosion:
  • Metals: Fe rusts (4Fe + 3O₂ + 2xH₂O → 2Fe₂O₃·xH₂O), prevented by galvanization (Zn coating).
  • Non-Metals: Chemically stable, no corrosion.
• Environmental Impact:
  • Metal mining pollutes water (e.g., Hg, Pb).
  • Non-metal oxides (e.g., SO₂, CO₂) cause acid rain, global warming.
• Applications in Exams: Extraction, alloys, and environmental impacts are key for objective and descriptive questions.

Formulas:

• Metal Extraction: ZnO + C → Zn + CO.
• Rusting: 4Fe + 3O₂ + 2xH₂O → 2Fe₂O₃·xH₂O.
• Reaction with Acid: M + 2HCl → MCl₂ + H₂ (e.g., Zn + 2HCl → ZnCl₂ + H₂).
• Non-Metal Oxide: S + O₂ → SO₂; SO₂ + H₂O → H₂SO₃.

Applications:

• Competitive Exams:
  • UPSC/PCS: Questions on metal extraction in industry or environmental impacts (e.g., acid rain from SO₂).
  • SSC: Objective questions on reactivity series, alloys, or corrosion.
  • Descriptive: Explain steel production or corrosion prevention.
• Real-World:
  • Industry: Al in aircraft, Cu in wiring.
  • Environment: Heavy metal pollution, non-metal oxides in air pollution.
  • Daily Life: Steel in construction, S in matches.
• Exam Tips:
  • Memorize reactivity series and extraction methods.
  • Link to environmental science (e.g., acid rain, metal pollution) for mains.

Diagram (Textual Description):

• Reactivity Series: A chart listing metals (K, Na, Ca, Mg, Al, Zn, Fe, Cu, Ag) from most to least reactive. Show reactions: Na with H₂O (H₂ gas), Fe with HCl (H₂ bubbles), Cu (no reaction). Label displacement reactions and corrosion susceptibility.

---

Class 11: Organic Chemistry – Basic Principles and Techniques

Detailed Concepts:

• Organic Chemistry: Study of carbon compounds (except CO, CO₂, carbonates).
• Unique Features of Carbon:
  • Catenation: Forms chains/rings (e.g., C₆H₁₄, cyclohexane).
  • Tetravalency: Four covalent bonds (e.g., CH₄).
  • Isomerism: Same formula, different structures (e.g., C₄H₁₀: n-butane, isobutane).
• Classification:
  • Hydrocarbons: Alkanes (CₙH₂ₙ₊₂), alkenes (CₙH₂ₙ), alkynes (CₙH₂ₙ₋₂), aromatics (e.g., C₆H₆).
  • Functional Groups: –OH (alcohol), –CHO (aldehyde), –COOH (acid), –NH₂ (amine).
• Nomenclature (IUPAC):
  • Longest carbon chain as root (e.g., pentane for C₅).
  • Functional group priority (e.g., –COOH > –OH > –NH₂).
  • Example: CH₃CH₂OH (ethanol), C₆H₅NH₂ (aniline).
• Isomerism:
  • Structural: Different connectivity (e.g., butane vs. isobutane).
  • Stereoisomerism: Same connectivity, different arrangement (e.g., cis/trans in alkenes).
• Bonding and Hybridization:
  • sp³: Tetrahedral, single bonds (e.g., CH₄, 109.5°).
  • sp²: Trigonal planar, double bonds (e.g., C₂H₄, 120°).
  • sp: Linear, triple bonds (e.g., C₂H₂, 180°).
• Reaction Types:
  • Substitution: Replacement (e.g., CH₄ + Cl₂ → CH₃Cl + HCl, UV).
  • Addition: Double/triple bond addition (e.g., C₂H₄ + Br₂ → C₂H₄Br₂).
  • Elimination: Loss of small molecule (e.g., C₂H₅OH → C₂H₄ + H₂O).
• Purification Techniques:
  • Crystallization: For solids (e.g., purifying naphthalene).
  • Distillation: For liquids (e.g., separating ethanol-water).
  • Chromatography: Differential adsorption (e.g., separating ink pigments).
• Qualitative Analysis:
  • C/H Detection: Burn to form CO₂, H₂O.
  • N/S/Halogens: Lassaigne’s test (e.g., Na + C + N → NaCN, detected as Prussian blue).
• Applications in Exams: Nomenclature, isomerism, and purification techniques are key for objective and descriptive questions.

Formulas:

• Alkanes: CₙH₂ₙ₊₂.
• Alkenes: CₙH₂ₙ.
• Alkynes: CₙH₂ₙ₋₂.
• Substitution: RH + X₂ → RX + HX.
• Lassaigne’s Test (Nitrogen): Na + C + N → NaCN; NaCN + FeSO₄ → Prussian blue.

Applications:

• Competitive Exams:
  • UPSC/PCS: Questions on organic compounds in industry (e.g., petrochemicals) or environmental contexts (e.g., VOCs).
  • SSC: Objective questions on nomenclature, isomerism, or purification.
  • Descriptive: Explain chromatography or hybridization in ethene.
• Real-World:
  • Industry: Synthesis of drugs, plastics.
  • Environment: VOCs in air pollution.
  • Research: Chromatography in forensics, drug analysis.
• Exam Tips:
  • Master IUPAC naming and isomerism types.
  • Link to environmental science (e.g., VOC emissions) for mains.

Diagram (Textual Description):

• Hybridization in Ethene: Show C₂H₄ with sp²-hybridized carbons (trigonal planar, 120°). Draw C=C double bond (σ + π), H atoms, and orbitals (sp² + p for π-bond). Label hybridization, bond angles, and π-bond.

---

Class 12: Chemistry in Everyday Life

Detailed Concepts:

• Chemicals in Medicines:
  • Analgesics: Pain relief (e.g., aspirin, C₉H₈O₄; paracetamol, non-narcotic).
  • Antibiotics: Kill bacteria (e.g., penicillin, inhibits cell wall synthesis).
  • Antacids: Neutralize stomach acid (e.g., Mg(OH)₂, NaHCO₃).
  • Antihistamines: Treat allergies (e.g., cetirizine).
• Chemicals in Food:
  • Preservatives: Prevent spoilage (e.g., sodium benzoate, C₆H₅COONa).
  • Artificial Sweeteners: Low-calorie (e.g., aspartame, 200× sweeter than sugar).
  • Antioxidants: Prevent oxidation (e.g., BHA, BHT in oils).
• Cleansing Agents:
  • Soaps: Na/K salts of fatty acids (e.g., C₁₇H₃₅COONa), form micelles.
  • Detergents: Synthetic, effective in hard water (e.g., sodium dodecylbenzene sulfonate).
• Environmental Impact:
  • Non-biodegradable detergents cause water pollution.
  • Antibiotics in wastewater lead to resistance.
• Dyes and Polymers:
  • Dyes: Organic compounds (e.g., azo dyes from diazonium salts).
  • Polymers: Plastics in packaging (e.g., polyethylene), biodegradable alternatives.
• Applications in Exams: Drug mechanisms, food additives, and environmental impacts are key for objective and descriptive questions.

Formulas:

• Soap Formation: RCOOH + NaOH → RCOONa + H₂O.
• Aspirin Synthesis: C₆H₅OH + (CH₃CO)₂O → C₉H₈O₄ (aspirin) + CH₃COOH.
• Neutralization (Antacid): HCl + NaHCO₃ → NaCl + H₂O + CO₂.
• Azo Dye Formation: C₆H₅N₂⁺Cl⁻ + C₆H₅OH → C₆H₅–N=N–C₆H₅OH + HCl.

Applications:

• Competitive Exams:
  • UPSC/PCS: Questions on drugs in health policy or detergents in environmental pollution.
  • SSC: Objective questions on drug types, soap vs. detergent, or food additives.
  • Descriptive: Explain antibiotic resistance or biodegradable detergents.
• Real-World:
  • Medicine: Aspirin for pain, antibiotics for infections.
  • Food: Preservatives in packaged goods, sweeteners in diet products.
  • Environment: Biodegradable soaps to reduce pollution.
• Exam Tips:
  • Master drug classifications and soap/detergent chemistry.
  • Link to environmental science (e.g., antibiotic resistance, detergent pollution) for mains.

Diagram (Textual Description):

• Soap Micelle in Action: Show a micelle with hydrophilic heads (–COO⁻) facing water and hydrophobic tails (hydrocarbon chains) trapping grease. Label micelle structure, grease molecule, and water, highlighting cleaning mechanism.