Aspirant Academy

Science and Technology

Key Points at a Glance

Chemistry: Atomic Structure, Metals & Non-Metals, Ores & Alloys, Acids/Bases/pH, Drugs, Pesticides, Carbon Compounds, Fuels, Radioactivity, Green Chemistry

Paper II · Unit 2 Section 1 of 13 0 PYQs 28 min
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Key Points at a Glance

  1. Atomic Structure

    • Atom has a nucleus (protons + neutrons) surrounded by electrons in energy shells
    • Atomic number (Z) = number of protons; uniquely identifies each element
    • Mass number (A) = protons + neutrons

  2. Isotopes

    • Atoms of the same element with same Z but different A
    • Example: Carbon-12 and Carbon-14
    • Carbon-14 used in radiocarbon dating; half-life = 5,730 years

  3. Metals vs Non-Metals

    • Metals: electropositive, malleable, ductile, good conductors
    • Non-metals: electronegative, brittle, poor conductors
    • Exception: graphite (non-metal, conducts electricity)
    • Exception: mercury (metal, liquid at room temperature)

  4. Key Ores

    • Bauxite — primary ore of aluminium
    • Haematite (Fe₂O₃) — iron ore
    • Galena (PbS) — lead ore
    • Chalcopyrite (CuFeS₂) — copper ore
    • India's bauxite reserves (~3 billion tonnes) are the 5th largest globally

  5. Alloys

    • Alloys are homogeneous mixtures of metals
    • Stainless steel: Fe + Cr (10–11%) + Ni — corrosion-resistant
    • Brass: Cu + Zn; Bronze: Cu + Sn
    • Duralumin: Al + Cu + Mn + Mg — used in aircraft
    • Solder: Pb + Sn — used for electrical joints

  6. pH Scale

    • pH scale ranges 0–14: pH < 7 = acidic; pH = 7 = neutral; pH > 7 = basic/alkaline
    • Human blood pH = 7.35–7.45
    • Stomach acid (HCl) pH ≈ 1.5–2
    • Seawater pH ≈ 8.1

  7. Drug Categories

    • Analgesics relieve pain: aspirin, paracetamol
    • Antibiotics kill/inhibit bacteria: penicillin (Alexander Fleming, 1928)
    • Antipyretics reduce fever
    • Antiseptics prevent infection on living tissue
    • Disinfectants kill microbes on non-living surfaces

  8. Pesticides

    • Organochlorine pesticides (DDT, BHC/lindane) — highly persistent, bioaccumulate in food chains
    • Most banned under the Stockholm Convention (2004)
    • Safer alternatives: neonicotinoids, pyrethroids, integrated pest management (IPM)

  9. Carbon Compounds

    • Carbon forms millions of compounds due to catenation (self-linking) and tetravalency (4 bonds)
    • Alkanes: CₙH₂ₙ₊₂ — saturated hydrocarbons
    • Alkenes: CₙH₂ₙ — one double bond
    • Alkynes: CₙH₂ₙ₋₂ — triple bond

  10. Petroleum and Fuels

    • Petroleum (crude oil) is a mixture of hydrocarbons, refined by fractional distillation
    • Fractions: LPG (below 30°C), petrol (30–70°C), kerosene (150–270°C), diesel (250–350°C)
    • Calorific values: hydrogen (142 MJ/kg) > LPG (~50) > petrol (~47) > coal (~30 MJ/kg)

  11. Radioactivity

    • Spontaneous emission of radiation from unstable nuclei
    • Alpha (α): helium nuclei (2p+2n); low penetration, stopped by paper
    • Beta (β): electrons or positrons; moderate penetration
    • Gamma (γ): high-energy EM radiation; highest penetration, stopped only by thick lead/concrete

  12. Green Chemistry

    • 12 Principles formulated by Paul Anastas & John Warner, 1998
    • Aims to reduce or eliminate hazardous substances in chemical design, synthesis, and use
    • Key principles: atom economy, renewable feedstocks, avoiding auxiliary solvents
    • Also: energy efficiency, catalytic reagents over stoichiometric

  13. Nuclear Fission vs Fusion

    • Nuclear fission: U-235 or Pu-239 splits; releases ~200 MeV per fission; powers reactors
    • Nuclear fusion: hydrogen isotopes form helium; releases ~17.6 MeV per D-T reaction
    • Fusion requires temperatures of ~100 million °C
    • Fusion is the energy source of the Sun

  14. Polymer Chemistry

    • Natural polymers: rubber (polyisoprene), cellulose, starch, proteins
    • Synthetic polymers: nylon (polyamide, 1935), PVC (polyvinyl chloride), Teflon (PTFE), Bakelite (first synthetic plastic, 1907)
    • Rubber vulcanisation: heating with sulphur (Charles Goodyear 1839) improves elasticity and durability