Topic 67: Chemistry – Atoms, Metals, Acids,

Q: What are isotopes? Give two examples and state one practical application of each.

**Isotopes** are atoms of the same element with identical atomic number (Z) but different mass numbers (A) — they differ in neutron count. Example 1: **Carbon-14** (Z=6, A=14, half-life 5,730 years) — used in **radiocarbon dating** to determine age of organic archaeological specimens. Example 2: **Iodine-131** (Z=53, A=131, half-life 8 days) — used in **thyroid cancer diagnosis and treatment** via targeted radiation.

Study Material

Paper Paper II

Unit 2

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

Key facts

Isotopes — Atoms of the same element with same Z but different A — Example: Carbon-12 and Carbon-14
Key Ores — Bauxite — primary ore of aluminium — Haematite (Fe₂O₃) — iron ore — Galena (PbS) — lead ore — Chalcopyrite (CuFeS₂) — copper ore
Alloys — Alloys are homogeneous mixtures of metals — Stainless steel: Fe + Cr (10–11%) + Ni — corrosion-resistant — Brass: Cu + Zn; Bronze: Cu + Sn
pH Scale — pH scale ranges 0–14: pH < 7 = acidic; pH = 7 = neutral; pH > 7 = basic/alkaline — Human blood pH = 7.35–7.45
Drug Categories — Analgesics relieve pain: aspirin, paracetamol — Antibiotics kill/inhibit bacteria: penicillin (Alexander Fleming, 1928)

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

Why does chemistry matter in the RPSC Science and Technology syllabus?

Chemistry matters in the RPSC Science and Technology syllabus because it links core scientific concepts with daily-life applications in water, agriculture, health, energy, materials and the environment.

Topic 67 is the foundational chemistry chapter for Paper II's Science & Technology unit. It covers the widest range of sub-domains — from the quantum world of atomic structure to everyday applications in medicines, fuels, and materials.

According to the RPSC syllabus page, the English Mains syllabus for the 2026 Rajasthan State and Subordinate Services Combined Competitive Examination was released on 09/01/2026.

PYQ data confirms this is one of the highest-scoring topics, appearing in all 5 exam years with a 6-year total of 51 marks.

Why Chemistry Dominates S&T Questions

The RPSC examiner draws on chemistry across daily life contexts:

Water purification (pH, bleaching powder)
Agriculture (fertilisers, pesticides)
Health (drugs, food additives)
Energy (fuels, nuclear power)
Environment (green chemistry, pollution)

The 2026 syllabus explicitly lists green chemistry and radioactivity, both of which have not been asked recently — making them high-probability questions.

Exam Approach for 50-Word Answers

Identify the concept → give its defining feature or formula → state 2–3 specific examples with names/numbers. Avoid vague descriptions — examiners reward precision.

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PREDICTED Predicted RAS Questions

Based on PYQ trends and 2026 syllabus analysis

1 5M What are isotopes? Give two examples and state one practical application of each. 5 marks · 50 words

Model Answer

Isotopes are atoms of the same element with identical atomic number (Z) but different mass numbers (A) — they differ in neutron count. Example 1: Carbon-14 (Z=6, A=14, half-life 5,730 years) — used in radiocarbon dating to determine age of organic archaeological specimens. Example 2: Iodine-131 (Z=53, A=131, half-life 8 days) — used in thyroid cancer diagnosis and treatment via targeted radiation.

~50 words • 5 marks