Chemistry Notes – Set 7: Detailed Guide for UPSC, PCS, SSC Competitive Exams

Class 9: Chemical Changes and Reactions

Detailed Concepts:

• Chemical Change: Transformation forming new substances with different properties, usually irreversible (e.g., burning wood → ash, CO₂, H₂O).
  • Characteristics:
    • New substances formed.
    • Change in color, smell, or state (e.g., rusting: Fe → Fe₂O₃, red-brown).
    • Gas evolution (e.g., Zn + HCl → H₂ gas).
    • Heat/light production or absorption (e.g., burning methane, exothermic).
• Physical Change: No new substance formed, reversible (e.g., melting ice, dissolving sugar).
• Types of Chemical Reactions (Simplified):
  • Combination: Two substances form one product (e.g., CaO + H₂O → Ca(OH)₂, slaking lime).
  • Decomposition: One substance breaks into two or more (e.g., CaCO₃ → CaO + CO₂, heating limestone).
  • Displacement: More reactive element displaces less reactive (e.g., Fe + CuSO₄ → FeSO₄ + Cu).
  • Precipitation: Insoluble product formed (e.g., AgNO₃ + NaCl → AgCl↓ + NaNO₃).
• Indicators of Chemical Change:
  • Gas bubbles (e.g., CO₂ from NaHCO₃ + acid).
  • Color change (e.g., CuSO₄·5H₂O (blue) → CuSO₄ (white) on heating).
  • Temperature change (e.g., exothermic: burning; endothermic: dissolving NH₄Cl).
• Chemical Equations:
  • Represent reactants and products (e.g., 2H₂ + O₂ → 2H₂O).
  • Balanced to conserve mass (equal atoms on both sides).
• Applications in Daily Life:
  • Cooking (e.g., baking soda decomposition: 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂).
  • Rusting, digestion (enzymatic reactions), photosynthesis (6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂).
• Applications in Exams: Understanding chemical vs. physical changes and reaction types is key for objective and descriptive questions.

Formulas:

• Combination: A + B → AB (e.g., 2Mg + O₂ → 2MgO).
• Decomposition: AB → A + B (e.g., 2H₂O → 2H₂ + O₂, electrolysis).
• Displacement: A + BC → AC + B (e.g., Zn + CuSO₄ → ZnSO₄ + Cu).
• Precipitation: AB + CD → AD↓ + CB (e.g., BaCl₂ + Na₂SO₄ → BaSO₄↓ + 2NaCl).

Applications:

• Competitive Exams:
  • UPSC/PCS: Questions on chemical changes in environmental contexts (e.g., photosynthesis, pollution) or industrial processes (e.g., lime production).
  • SSC: Objective questions on reaction types, indicators of chemical change, or balancing equations.
  • Descriptive: Explain chemical changes in cooking or rusting prevention.
• Real-World:
  • Industry: Limestone decomposition in cement production.
  • Environment: Photosynthesis in carbon cycle, combustion in pollution.
  • Daily Life: Baking, fermentation (e.g., ethanol production in wine).
• Exam Tips:
  • Focus on identifying chemical changes and reaction types for objective questions.
  • Link to environmental science (e.g., CO₂ in climate change) for mains.

Diagram (Textual Description):

• Precipitation Reaction: Show BaCl₂ + Na₂SO₄ → BaSO₄↓ + 2NaCl. A beaker with BaCl₂ solution mixed with Na₂SO₄, forming white BaSO₄ precipitate at the bottom. Label reactants, precipitate, and soluble products (NaCl in solution).

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Class 10: Environmental Chemistry

Detailed Concepts:

• Environmental Chemistry: Study of chemical processes in the environment (air, water, soil) and their impact.
• Air Pollution:
  • Pollutants:
    • Gases: CO, CO₂, SO₂, NOₓ (NO, NO₂), volatile organic compounds (VOCs).
    • Particulate Matter: PM2.5, PM10 (e.g., soot, dust).
  • Sources:
    • Combustion of fossil fuels (e.g., CO₂, SO₂ from coal).
    • Vehicle emissions (NOₓ, CO).
    • Industrial processes, biomass burning.
  • Effects:
    • Acid Rain: SO₂ + H₂O → H₂SO₃ → H₂SO₄; NO₂ → HNO₃. Damages soil, water, buildings.
    • Smog: Photochemical (NOₓ + VOCs + sunlight → ozone) or classical (SO₂ + particulates).
    • Global Warming: CO₂, CH₄ trap heat (greenhouse effect).
• Water Pollution:
  • Pollutants: Heavy metals (e.g., Hg, Pb), organic waste, fertilizers (nitrates, phosphates).
  • Eutrophication: Excess nutrients cause algal blooms, depleting O₂ (e.g., NO₃⁻ → algae → low O₂).
  • Chemical Reactions: Heavy metals form complexes (e.g., Hg²⁺ in water), organic waste decomposition (CH₂O → CO₂ + H₂O).
• Soil Pollution:
  • Pollutants: Pesticides, heavy metals, industrial waste.
  • Impact: Affects soil pH, fertility (e.g., Pb²⁺ accumulation).
• Ozone Layer:
  • Stratospheric O₂ → O₃ by UV, protects from UV radiation.
  • Depleted by CFCs (e.g., CF₂Cl₂ → Cl· radicals, catalyze O₃ → O₂).
• Green Chemistry:
  • Sustainable practices to reduce pollution (e.g., biodegradable detergents, renewable feedstocks).
• Applications in Exams: Pollution reactions, 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.
• Combustion (Pollution): C + O₂ → CO₂; 2C + O₂ → 2CO (incomplete).

Applications:

• Competitive Exams:
  • UPSC/PCS: Questions on pollution chemistry (e.g., acid rain, ozone depletion) or green chemistry in policy.
  • SSC: Objective questions on pollutants, reactions, or environmental impacts.
  • Descriptive: Explain acid rain formation or green chemistry solutions.
• Real-World:
  • Environment: Scrubbers to remove SO₂, catalytic converters for NOₓ, CO.
  • Industry: Green synthesis of chemicals, biodegradable plastics.
  • Health: Heavy metal removal from water (e.g., activated carbon).
• Exam Tips:
  • Master pollution reactions and their environmental effects.
  • Link to environmental science (e.g., climate change, water treatment) for mains.

Diagram (Textual Description):

• Acid Rain Formation: Show SO₂ emitted from a factory, reacting with H₂O and O₂ in air to form H₂SO₄ droplets in clouds. Rain falls, affecting soil and water. Label SO₂, H₂SO₄, and environmental impact (e.g., damaged trees).

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Class 11: Hydrogen

Detailed Concepts:

• Hydrogen: Simplest element (Z = 1), exists as H₂ gas, highly reactive, abundant in universe.
• Isotopes:
  • Protium (¹H): 1 proton, 0 neutrons, most abundant.
  • Deuterium (²H or D): 1 proton, 1 neutron, used in heavy water (D₂O).
  • Tritium (³H): 1 proton, 2 neutrons, radioactive, used in nuclear reactions.
• Physical Properties:
  • Colorless, odorless, diatomic gas (H₂), low density (0.089 g/L), low boiling point (–252.8°C).
• Chemical Properties:
  • Combustion: 2H₂ + O₂ → 2H₂O, highly exothermic (ΔH = –286 kJ/mol for liquid H₂O).
  • Reduction: Reduces metal oxides (e.g., CuO + H₂ → Cu + H₂O).
  • Addition: Adds to unsaturated hydrocarbons (e.g., C₂H₄ + H₂ → C₂H₆, Ni catalyst).
• Preparation:
  • Laboratory: Zn + 2HCl → ZnCl₂ + H₂.
  • Industrial: Electrolysis of H₂O (2H₂O → 2H₂ + O₂); steam reforming of CH₄ (CH₄ + H₂O → CO + 3H₂).
• Hydrides:
  • Ionic: Formed by alkali/alkaline earth metals (e.g., NaH, CaH₂), release H⁻.
  • Covalent: Non-metals (e.g., H₂O, NH₃), polar or non-polar.
  • Metallic: Transition metals (e.g., TiH₂), used in hydrogen storage.
• Water:
  • Structure: H₂O, bent, polar (104.5° bond angle), hydrogen bonding causes high boiling point (100°C).
  • Hardness: Due to Ca²⁺, Mg²⁺ ions, removed by boiling (temporary) or ion exchange (permanent).
• Hydrogen Peroxide (H₂O₂):
  • Preparation: BaO₂ + H₂SO₄ → BaSO₄ + H₂O₂.
  • Properties: Oxidizing agent (H₂O₂ → 2H₂O + O), bleaching agent.
• Hydrogen Economy: H₂ as clean fuel (produces H₂O), challenges in storage/production.
• Applications in Exams: Hydrogen’s properties, hydrides, and water chemistry are key for objective and descriptive questions.

Formulas:

• Combustion: 2H₂ + O₂ → 2H₂O.
• Steam Reforming: CH₄ + H₂O → CO + 3H₂.
• H₂O₂ Decomposition: 2H₂O₂ → 2H₂O + O₂.
• Electrolysis: 2H₂O → 2H₂ + O₂.

Applications:

• Competitive Exams:
  • UPSC/PCS: Questions on hydrogen as fuel or water chemistry in environmental contexts.
  • SSC: Objective questions on hydrogen preparation, hydrides, or H₂O₂ uses.
  • Descriptive: Explain hydrogen economy or water hardness removal.
• Real-World:
  • Energy: H₂ in fuel cells for clean energy.
  • Industry: Ammonia synthesis (N₂ + 3H₂ → 2NH₃), H₂O₂ in bleaching.
  • Environment: Water purification, H₂ as renewable fuel.
• Exam Tips:
  • Focus on hydrogen’s preparation and applications for objective questions.
  • Link to environmental science (e.g., hydrogen fuel, water treatment) for mains.

Diagram (Textual Description):

• Water Structure: Show H₂O molecule, bent shape (104.5°), with O at center, two H atoms, and two lone pairs. Dotted lines indicate hydrogen bonds between molecules, explaining high boiling point. Label polarity (O δ⁻, H δ⁺).

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Class 12: Biomolecules

Detailed Concepts:

• Biomolecules: Organic molecules essential for life (carbohydrates, proteins, lipids, nucleic acids).
• Carbohydrates:
  • Classification:
    • Monosaccharides: Simple sugars (e.g., glucose, fructose, C₆H₁₂O₆).
    • Disaccharides: Two monosaccharides (e.g., sucrose: glucose + fructose, C₁₂H₂₂O₁₁).
    • Polysaccharides: Multiple units (e.g., starch, cellulose, glycogen).
  • Structure: Glucose (C₆H₁₂O₆) exists as open chain or cyclic (pyranose/furanose).
  • Functions: Energy source (glucose), storage (starch), structural (cellulose).
• Proteins:
  • Structure: Polymers of amino acids (20 types, e.g., glycine, alanine) linked by peptide bonds.
    • Primary: Amino acid sequence.
    • Secondary: α-helix, β-sheet (H-bonding).
    • Tertiary: 3D folding (H-bonds, disulfide bonds, hydrophobic interactions).
    • Quaternary: Multiple polypeptide chains (e.g., hemoglobin).
  • Functions: Enzymes (catalysis), structural (keratin), transport (hemoglobin).
• Lipids:
  • Types: Fats, oils, phospholipids, steroids.
  • Structure: Fatty acids (e.g., stearic acid, C₁₇H₃₅COOH) esterified with glycerol (triglycerides).
  • Functions: Energy storage, membrane structure, hormones (steroids).
• Nucleic Acids:
  • DNA: Deoxyribonucleic acid, double helix, stores genetic information (bases: A, T, C, G).
  • RNA: Ribonucleic acid, single-stranded, protein synthesis (bases: A, U, C, G).
  • Structure: Nucleotides (sugar + base + phosphate), linked by phosphodiester bonds.
• Enzymes:
  • Protein catalysts, specific, lower activation energy.
  • Example: Amylase breaks starch into glucose.
• Applications in Exams: Structures, functions, and biochemical reactions are key for objective and descriptive questions.

Formulas:

• Glucose: C₆H₁₂O₆ (open chain: CHO–(CHOH)₄–CH₂OH).
• Sucrose Hydrolysis: C₁₂H₂₂O₁₁ + H₂O → C₆H₁₂O₆ (glucose) + C₆H₁₂O₆ (fructose).
• Peptide Bond: R–COOH + H₂N–R’ → R–CONH–R’ + H₂O.
• Nucleotide: Sugar + Base + Phosphate.

Applications:

• Competitive Exams:
  • UPSC/PCS: Questions on biomolecules in nutrition or biotechnology (e.g., DNA in forensics).
  • SSC: Objective questions on carbohydrate/protein structures or enzyme functions.
  • Descriptive: Explain enzyme catalysis or DNA’s role in genetics.
• Real-World:
  • Medicine: Insulin (protein) for diabetes, DNA in genetic testing.
  • Industry: Enzymes in food processing (e.g., amylase in brewing).
  • Nutrition: Carbohydrates in energy, lipids in diets.
• Exam Tips:
  • Master biomolecule structures and enzyme functions for objective questions.
  • Link to biotechnology or environmental science (e.g., biodegradable polymers) for mains.

Diagram (Textual Description):

• DNA Double Helix: Two strands of nucleotides (sugar-phosphate backbone, A-T, C-G base pairs via H-bonds). Show ladder-like structure, twisted into helix. Label bases, phosphodiester bonds, and H-bonding (A=T, C≡G).