Chemistry Notes – Set 13: Detailed Guide for UPSC, PCS, SSC Competitive Exams

By /

Class 9: Introduction to Atoms and Molecules

Detailed Concepts:

  • Atoms: Smallest unit of an element retaining its properties.
    • Structure: Nucleus (protons, neutrons), electrons in shells (e.g., Na: 2,8,1).
    • Atomic Number (Z): Number of protons (e.g., C: Z = 6).
    • Mass Number (A): Protons + neutrons (e.g., C-12: A = 12).
    • Isotopes: Same Z, different A (e.g., C-12, C-14).
  • Molecules: Two or more atoms bonded (e.g., O₂, H₂O).
    • Types: Homoatomic (e.g., N₂), heteroatomic (e.g., CO₂).
    • Molecular Mass: Sum of atomic masses (e.g., H₂O: 2×1 + 16 = 18 u).
  • Mole Concept:
    • Mole: Amount containing Avogadro’s number (6.022×10²³) particles.
    • Molar Mass: Mass of 1 mole (e.g., CO₂: 12 + 2×16 = 44 g/mol).
    • Formula: Number of moles = Mass/Molar mass.
  • Chemical Behavior:
    • Valency: Combining capacity (e.g., Na: 1, O: 2).
    • Bonding: Ionic (e.g., NaCl, electron transfer), covalent (e.g., CH₄, electron sharing).
    • Reactions: Atoms rearrange to form molecules (e.g., 2H₂ + O₂ → 2H₂O).
  • Applications:
    • Industrial: Molecular mass in chemical synthesis (e.g., NH₃ production).
    • Environmental: CO₂ in carbon cycle, isotopes in dating (C-14).
    • Daily Life: H₂O in hydration, O₂ in respiration.
  • Applications in Exams: Atomic structure, mole concept, and applications are key for objective and descriptive questions.

Formulas:

  • Mole: Moles = Mass/Molar mass.
  • Molecular Mass: Sum of atomic masses (e.g., NH₃: 14 + 3×1 = 17 u).
  • Percentage Composition: % = (n × Atomic mass / Molecular mass) × 100.
  • Avogadro’s Number: 6.022×10²³ particles/mol.

Applications:

  • Competitive Exams:
    • UPSC/PCS: Questions on isotopes in environmental science (e.g., C-14 dating) or mole concept in industry.
    • SSC: Objective questions on atomic structure, valency, or mole calculations.
    • Descriptive: Explain mole concept or isotope applications.
  • Real-World:
    • Industry: Mole calculations in fertilizer synthesis (NH₃).
    • Environment: Isotopes in climate studies, CO₂ in greenhouse effect.
    • Daily Life: Molecular understanding in food (e.g., glucose, C₆H₁₂O₆).
  • Exam Tips:
    • Master mole calculations and valency.
    • Link to environmental science (e.g., isotopes in archaeology) for mains.

Diagram (Textual Description):

  • Atomic Structure of Carbon: Show C atom with nucleus (6 protons, 6 neutrons) and electron shells (2,4). Label atomic number (Z = 6), mass number (A = 12), and valence electrons (4, explaining tetravalency). Include C-14 isotope (8 neutrons).

Class 10: Sources of Energy [Fuels and Combustion]

Detailed Concepts:

  • Note: Revisiting Set 6’s “Sources of Energy [Fuels and Combustion]” with a focus on chemical energy, combustion reactions, and environmental impacts to avoid redundancy, tailored for Class 10 level and exam needs.
  • Fuels: Substances releasing energy via combustion.
    • Types:
      • Fossil Fuels: Coal (C), petroleum (hydrocarbons), natural gas (CH₄).
      • Biofuels: Ethanol (C₂H₅OH), biogas (CH₄ + CO₂).
    • Characteristics: High calorific value (e.g., CH₄: 55 MJ/kg), availability.
  • Combustion:
    • Complete: Fuel + O₂ → CO₂ + H₂O (e.g., CH₄ + 2O₂ → CO₂ + 2H₂O, exothermic).
    • Incomplete: Limited O₂, forms CO, soot (e.g., 2C + O₂ → 2CO).
    • Calorific Value: Energy released per unit mass (kJ/kg).
  • Chemical Reactions:
    • Petrol: C₈H₁₈ + 12.5O₂ → 8CO₂ + 9H₂O.
    • Ethanol: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O.
  • Environmental Impacts:
    • Pollution: CO₂ (greenhouse gas), CO (toxic), SO₂ (acid rain from coal).
    • Renewable Fuels: Ethanol reduces CO₂ emissions vs. fossil fuels.
  • Applications:
    • Energy: Fuels in vehicles, power plants.
    • Industrial: Coal in steel, biofuels in green energy.
    • Environmental: Shift to renewables to curb emissions.
  • Applications in Exams: Combustion reactions and environmental impacts are key for objective and descriptive questions.

Formulas:

  • Methane Combustion: CH₄ + 2O₂ → CO₂ + 2H₂O.
  • Octane Combustion: 2C₈H₁₈ + 25O₂ → 16CO₂ + 18H₂O.
  • Incomplete Combustion: 2C + O₂ → 2CO.
  • Calorific Value: Energy (kJ)/Mass (kg).

Applications:

  • Competitive Exams:
    • UPSC/PCS: Questions on fuels in energy policy or environmental impacts (e.g., CO₂ in climate change).
    • SSC: Objective questions on combustion reactions or fuel types.
    • Descriptive: Explain biofuel advantages or pollution from fossil fuels.
  • Real-World:
    • Energy: Natural gas in power plants, ethanol in vehicles.
    • Environment: Biofuels for lower emissions, SO₂ scrubbers in industry.
    • Industry: Coal in cement, biofuels in sustainable energy.
  • Exam Tips:
    • Master combustion equations and calorific values.
    • Link to environmental science (e.g., greenhouse gases) for mains.

Diagram (Textual Description):

  • Combustion of Methane: Show CH₄ reacting with O₂ in a flame, forming CO₂ and H₂O. Draw tetrahedral CH₄, linear CO₂, and bent H₂O. Label exothermic heat, CO₂ (greenhouse gas), and flame characteristics.

Class 11: Environmental Chemistry

Detailed Concepts:

  • Note: This topic complements Set 7’s Class 10 “Environmental Chemistry” by focusing on Class 11-level depth, emphasizing atmospheric chemistry, water pollution, and green chemistry.
  • Atmospheric Pollution:
    • Tropospheric:
      • Pollutants: CO, NOₓ, SO₂, VOCs, particulate matter (PM2.5, PM10).
      • Smog:
        • Classical: SO₂ + particulates (e.g., London smog).
        • Photochemical: NOₓ + VOCs + sunlight → O₃ (e.g., urban smog).
      • Acid Rain: SO₂ + H₂O → H₂SO₃ → H₂SO₄; NO₂ → HNO₃.
    • Stratospheric:
      • Ozone Depletion: CFCs → Cl· radicals, catalyze O₃ → O₂.
  • Water Pollution:
    • Pollutants: Heavy metals (Hg, Pb), organic waste, nitrates/phosphates.
    • Eutrophication: Nutrient excess → algal blooms → O₂ depletion.
    • Chemical Reactions: Organic waste → CO₂ + H₂O (decomposition), Pb²⁺ forms complexes.
  • Soil Pollution:
    • Pollutants: Pesticides, heavy metals.
    • Impact: Reduced fertility, bioaccumulation (e.g., DDT).
  • Green Chemistry:
    • Sustainable practices (e.g., biodegradable polymers, renewable feedstocks).
    • Examples: Using H₂O₂ instead of Cl₂ for bleaching, green solvents.
  • Applications in Exams: Pollution mechanisms, ozone depletion, and green chemistry are key for objective and descriptive questions.

Formulas:

  • Acid Rain: SO₂ + H₂O → H₂SO₃; 2H₂SO₃ + O₂ → 2H₂SO₄.
  • Ozone Formation: 3O₂ → 2O₃ (UV light).
  • Ozone Depletion: CF₂Cl₂ → CF₂Cl· + Cl·; Cl· + O₃ → ClO· + O₂.
  • Eutrophication: NO₃⁻ → algal growth → O₂ depletion.

Applications:

  • Competitive Exams:
    • UPSC/PCS: Questions on pollution in environmental policy or green chemistry solutions.
    • SSC: Objective questions on smog, acid rain, or ozone depletion.
    • Descriptive: Explain green chemistry or ozone depletion mechanisms.
  • Real-World:
    • Environment: Catalytic converters (NOₓ, CO → N₂, CO₂), activated carbon for water treatment.
    • Industry: Green solvents, biodegradable detergents.
    • Health: Heavy metal removal from water.
  • Exam Tips:
    • Master pollution reactions and green chemistry principles.
    • Link to environmental science (e.g., climate change, water treatment) for mains.

Diagram (Textual Description):

  • Ozone Depletion: Show stratosphere with O₃ molecules, CFC (CF₂Cl₂) releasing Cl· radical, catalyzing O₃ → O₂. Label Cl· + O₃ → ClO· + O₂, UV radiation, and ozone hole formation.

Class 12: General Principles and Processes of Isolation of Elements

Detailed Concepts:

  • Occurrence of Metals:
    • Native: Ag, Au (uncombined).
    • Ores: Oxides (e.g., Fe₂O₃), sulfides (e.g., ZnS), carbonates (e.g., CaCO₃).
  • Concentration of Ores:
    • Froth Flotation: Sulfide ores (e.g., ZnS separated using pine oil).
    • Magnetic Separation: Magnetic ores (e.g., Fe₃O₄).
    • Leaching: Chemical dissolution (e.g., Al₂O₃ + NaOH → NaAlO₂, bauxite).
  • Extraction:
    • Pyrometallurgy: High-temperature reduction (e.g., Fe₂O₃ + 3CO → 2Fe + 3CO₂, blast furnace).
    • Hydrometallurgy: Aqueous leaching (e.g., Au + CN⁻ → [Au(CN)₂]⁻).
    • Electrometallurgy: Electrolysis (e.g., NaCl → Na + Cl₂, Al₂O₃ → Al + O₂).
  • Refining:
    • Distillation: Low boiling metals (e.g., Hg, Zn).
    • Liquation: Low melting metals (e.g., Sn).
    • Electrolytic Refining: Cu, Al (e.g., CuSO₄ electrolysis, pure Cu at cathode).
  • Thermodynamic Principles:
    • Ellingham Diagram: Predicts reduction feasibility (e.g., C reduces Fe₂O₃ at high T).
    • Gibbs Free Energy: ΔG = ΔH – TΔS, negative for spontaneous reduction.
  • Applications:
    • Industrial: Fe in steel, Al in packaging, Cu in wiring.
    • Environmental: Mining waste, energy-intensive processes.
  • Applications in Exams: Extraction processes, thermodynamics, and environmental impacts are key for objective and descriptive questions.

Formulas:

  • Iron Extraction: Fe₂O₃ + 3CO → 2Fe + 3CO₂.
  • Aluminum Extraction: 2Al₂O₃ → 4Al + 3O₂ (electrolysis).
  • Leaching (Bauxite): Al₂O₃ + 2NaOH + 3H₂O → 2NaAl(OH)₄.
  • Gibbs Equation: ΔG = ΔH – TΔS.

Applications:

  • Competitive Exams:
    • UPSC/PCS: Questions on metal extraction in industry or environmental impacts (e.g., mining pollution).
    • SSC: Objective questions on extraction methods or refining.
    • Descriptive: Explain blast furnace or Ellingham diagram.
  • Real-World:
    • Industry: Steel production, Al in aircraft.
    • Environment: Recycling metals to reduce mining.
    • Technology: Cu in electronics.
  • Exam Tips:
    • Master extraction methods and thermodynamics.
    • Link to environmental science (e.g., mining waste) for mains.

Diagram (Textual Description):

  • Blast Furnace for Iron: Show furnace with layers of Fe₂O₃, coke (C), limestone (CaCO₃). Label reactions: C + O₂ → CO₂, CO₂ + C → 2CO, Fe₂O₃ + 3CO → 2Fe + 3CO₂. Show molten Fe and slag (CaSiO₃) at bottom.

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top