BharatNotes
Overview
Organic chemistry, polymers, and environmental chemistry are frequently tested in UPSC Prelims — questions cover hydrocarbons, plastic types, ozone depletion, greenhouse gases, and pollution chemistry. This topic focuses on concepts and exam-relevant facts rather than reactions or equations.
Organic Chemistry Basics
Carbon — The Backbone Element
| Property | Detail |
|---|---|
| Tetravalency | Carbon has 4 valence electrons — can form 4 covalent bonds, allowing it to bond with hydrogen, oxygen, nitrogen, and other carbon atoms |
| Catenation | Carbon's unique ability to form long chains, branched chains, and rings by bonding with other carbon atoms — this is why millions of organic compounds exist |
| Isomerism | Same molecular formula but different structural arrangements — e.g., butane (C₄H₁₀) has two isomers: n-butane and isobutane |
Hydrocarbons
Hydrocarbons are compounds containing only carbon and hydrogen.
| Type | Bonding | General Formula | Examples |
|---|---|---|---|
| Alkanes | Single bonds only (C–C) | CₙH₂ₙ₊₂ | Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈) |
| Alkenes | At least one double bond (C=C) | CₙH₂ₙ | Ethylene/Ethene (C₂H₄), Propene (C₃H₆) |
| Alkynes | At least one triple bond | CₙH₂ₙ₋₂ | Acetylene/Ethyne (C₂H₂) |
Saturated hydrocarbons (alkanes) — all single bonds; relatively unreactive; burn with a clean blue flame.
Unsaturated hydrocarbons (alkenes, alkynes) — contain double/triple bonds; more reactive; burn with a sooty yellow flame; decolourise bromine water (test for unsaturation).
Functional Groups
Functional groups determine the chemical properties of organic compounds.
| Functional Group | Structure | Class of Compounds | Example |
|---|---|---|---|
| Hydroxyl (–OH) | –OH attached to carbon | Alcohols | Ethanol (C₂H₅OH) — used in beverages, antiseptics, fuel |
| Aldehyde (–CHO) | –C(=O)H | Aldehydes | Formaldehyde (HCHO) — used in preservation, Bakelite production |
| Ketone (>C=O) | C=O between two carbons | Ketones | Acetone (CH₃COCH₃) — common solvent, nail polish remover |
| Carboxyl (–COOH) | –C(=O)OH | Carboxylic Acids | Acetic acid (CH₃COOH) — vinegar; Citric acid — in citrus fruits |
| Amine (–NH₂) | –NH₂ attached to carbon | Amines | Methylamine (CH₃NH₂) — fishy odour; amino acids contain amine groups; amines are basic in nature |
| Ester (–COO–) | –C(=O)O– linking two carbons | Esters | Ethyl acetate (CH₃COOC₂H₅) — fruity smell, used in perfumes and flavouring; formed by reaction of alcohol + carboxylic acid (esterification) |
Biomolecules
Biomolecules are organic molecules essential for life processes. The four major classes are:
| Biomolecule | Building Blocks | Key Functions | Examples |
|---|---|---|---|
| Carbohydrates | Monosaccharides (simple sugars) | Energy source, structural support | Glucose (C₆H₁₂O₆) — primary energy molecule; Sucrose — table sugar; Cellulose — plant cell walls; Starch and glycogen — energy storage |
| Proteins | Amino acids (20 standard types) | Enzymes, structural support, transport, immunity, hormones | Haemoglobin (oxygen transport), Insulin (hormone), Keratin (hair, nails), Collagen (connective tissue) |
| Lipids | Fatty acids + glycerol | Energy storage, cell membrane structure, insulation, hormone synthesis | Fats and oils (triglycerides), Phospholipids (cell membranes), Cholesterol, Waxes |
| Nucleic Acids | Nucleotides (sugar + phosphate + nitrogenous base) | Storage and transmission of genetic information | DNA (deoxyribonucleic acid) — double helix, carries hereditary information; RNA (ribonucleic acid) — single-stranded, involved in protein synthesis |
Enzymes are biological catalysts — proteins that speed up biochemical reactions without being consumed. Each enzyme is specific to a particular substrate (lock-and-key model). Example: amylase in saliva breaks down starch into maltose.
Vitamins — Classification
| Type | Vitamins | Key Feature |
|---|---|---|
| Fat-soluble | A, D, E, K | Dissolve in fat; stored in the liver and fatty tissues; do not need daily intake; excess can cause toxicity |
| Water-soluble | B-complex (B₁, B₂, B₃, B₅, B₆, B₇, B₉, B₁₂) and C | Dissolve in water; not stored in the body; must be consumed daily; excess is excreted in urine; easily destroyed by cooking and food processing |
Deficiency diseases (frequently asked): Vitamin A — night blindness; Vitamin B₁ (Thiamine) — beriberi; Vitamin B₃ (Niacin) — pellagra; Vitamin C — scurvy; Vitamin D — rickets (children), osteomalacia (adults); Vitamin K — impaired blood clotting.
Polymers
Polymers are large molecules (macromolecules) made by linking many small repeating units called monomers.
Natural Polymers
| Polymer | Monomer | Source/Use |
|---|---|---|
| Natural rubber | Isoprene (C₅H₈) | Latex of rubber trees; used in tyres, gloves |
| Silk | Amino acids (fibroin protein) | Silkworm cocoons; textile fibre |
| Cellulose | Glucose (C₆H₁₂O₆) | Plant cell walls; paper, cotton |
| Starch | Glucose | Energy storage in plants; food |
| Proteins | Amino acids | Structural and functional roles in living organisms |
| DNA | Nucleotides | Genetic information carrier |
Synthetic Polymers
| Polymer | Monomer | Key Properties & Uses |
|---|---|---|
| Polyethylene (PE) | Ethylene (C₂H₄) | Most widely used plastic; carry bags, bottles, packaging |
| PVC (Polyvinyl Chloride) | Vinyl chloride | Pipes, cable insulation, flooring; rigid or flexible |
| Nylon (Polyamide) | Hexamethylenediamine + adipic acid | First fully synthetic fibre (synthesised 1935; commercialised 1938); ropes, clothing, toothbrush bristles |
| Teflon (PTFE) | Tetrafluoroethylene | Non-stick coating (cookware); chemically inert; heat-resistant |
| Bakelite | Phenol + Formaldehyde | First synthetic plastic (1907); electrical switches, handles — thermosetting |
| Polystyrene (PS) | Styrene | Packaging (Thermocol/Styrofoam); disposable cups |
| PET | Ethylene glycol + terephthalic acid | Water bottles, polyester fabric; widely recycled |
Plastics — Thermoplastics vs Thermosetting
| Property | Thermoplastics | Thermosetting Plastics |
|---|---|---|
| Behaviour on heating | Soften and can be remoulded repeatedly | Harden permanently; cannot be reshaped once set |
| Structure | Linear or slightly branched chains | Heavily cross-linked 3D network |
| Examples | Polyethylene, PVC, PET, polystyrene, nylon | Bakelite, melamine, epoxy resin |
| Recyclability | Recyclable | Not easily recyclable |
Plastic Recycling Codes (Resin Identification Codes)
| Code | Abbreviation | Full Name | Common Products |
|---|---|---|---|
| 1 | PET/PETE | Polyethylene Terephthalate | Water/soft drink bottles |
| 2 | HDPE | High-Density Polyethylene | Milk jugs, detergent bottles |
| 3 | PVC | Polyvinyl Chloride | Pipes, shrink wrap, medical tubes |
| 4 | LDPE | Low-Density Polyethylene | Grocery bags, food wrapping |
| 5 | PP | Polypropylene | Yoghurt containers, bottle caps |
| 6 | PS | Polystyrene | Disposable cups, Thermocol |
| 7 | Other | Mixed/other plastics | Polycarbonate, nylon, acrylic |
India's Single-Use Plastic Ban
India banned the manufacture, import, sale, and use of identified single-use plastic items with effect from 1 July 2022 under the Plastic Waste Management Amendment Rules, 2021 (notified 12 August 2021). Banned items include: plastic earbuds, balloon sticks, flags, candy sticks, ice-cream sticks, polystyrene (Thermocol) for decoration, plates, cups, glasses, cutlery (forks, spoons, knives), straws, trays, wrapping films around sweet boxes, invitation cards, cigarette packets, PVC banners less than 100 microns, and stirrers. Plastic carry bags must be at least 120 microns thick (from 31 December 2022).
Extended Producer Responsibility (EPR): The Plastic Waste Management Amendment Rules, 2022 (notified 16 February 2022) mandate EPR guidelines for plastic packaging — producers, importers, and brand owners (PIBOs) must establish systems for collection, recycling, and reuse of plastic packaging waste, with mandatory recycling targets phased in until FY 2027–28. The CPCB launched a centralised EPR portal for plastic packaging on 5 April 2022.
Microplastics — An Emerging Concern
| Aspect | Detail |
|---|---|
| Definition | Tiny plastic fragments less than 5 mm in size; classified as large microplastics (5 mm–1 mm) and small microplastics (1 mm–1 μm) |
| Primary microplastics | Intentionally manufactured at small size — microbeads in face washes, toothpastes, cosmetics; industrial abrasives |
| Secondary microplastics | Result from fragmentation of larger plastic debris through UV radiation, weathering, and mechanical abrasion — e.g., from plastic bags, bottles, synthetic textiles, tyre wear |
| In human blood | A 2022 Dutch study (Vrije Universiteit Amsterdam, published in Environment International) detected microplastics in human blood for the first time — found in 77% of 22 healthy volunteers; PET (50%), polystyrene (36%), and polyethylene (23%) were the most common types |
| Environmental impact | Enter food chains via water and soil; consumed by marine organisms → bioaccumulation and biomagnification; found in seafood, drinking water, table salt, and even the air |
Bioplastics and Biodegradable Alternatives
| Type | Source | Key Properties |
|---|---|---|
| PLA (Polylactic Acid) | Fermented plant starch (corn, sugarcane, sugar beet) | Biodegradable under industrial composting conditions (~58 °C); used in packaging, disposable tableware, 3D printing; degrades slowly in natural environments |
| PHA (Polyhydroxyalkanoates) | Synthesised by bacteria as carbon/energy storage granules | Biodegradable in soil, freshwater, and marine environments; degrades faster than PLA under natural conditions; used in packaging, medical sutures |
Limitation: Bioplastics currently account for a small fraction of global plastic production. Most require industrial composting facilities (not home composting) to degrade effectively, and they can contaminate conventional plastic recycling streams if mixed.
Biodegradable vs Non-Biodegradable Materials
| Aspect | Biodegradable | Non-Biodegradable |
|---|---|---|
| Definition | Broken down by microorganisms (bacteria, fungi) into simpler, harmless substances | Cannot be decomposed by biological processes; persist in the environment for decades or centuries |
| Time to decompose | Days to months | Hundreds to thousands of years |
| Examples | Vegetable peels, paper, cotton, wood, cow dung, food waste | Plastics, glass, aluminium cans, Styrofoam, synthetic rubber |
| Disposal | Composting, biogas production, vermicomposting | Recycling, incineration, landfill |
Composting — Aerobic decomposition of organic waste into nutrient-rich humus; reduces landfill burden and produces natural fertiliser.
Ozone Layer
| Aspect | Detail |
|---|---|
| What is ozone? | O₃ — a molecule of three oxygen atoms; found mainly in the stratosphere (15–35 km altitude) |
| Formation (Chapman Cycle) | UV radiation splits O₂ → 2O (atomic oxygen); atomic oxygen combines with O₂ → O₃; this cycle continuously regenerates ozone while absorbing harmful UV-B and UV-C radiation |
| Ozone hole | Severe depletion of the ozone layer, primarily over Antarctica; discovered in 1985 by Farman, Gardiner, and Shanklin |
| CFCs (Chlorofluorocarbons) | Synthetic chemicals (used in refrigerants, aerosol sprays); extremely stable — survive long enough to reach the stratosphere |
| Destruction mechanism | UV light breaks CFC molecules, releasing chlorine atoms; each chlorine atom acts as a catalyst, destroying thousands of ozone molecules (Cl + O₃ → ClO + O₂; ClO + O → Cl + O₂ — chlorine is regenerated) |
| Montreal Protocol (1987) | International treaty to phase out ODS (ozone-depleting substances) — CFCs, halons, carbon tetrachloride; achieved universal ratification (all 198 UN members); ozone layer is now slowly recovering |
| Kigali Amendment (2016) | Adopted on 15 October 2016 in Kigali, Rwanda; extends Montreal Protocol to phase down HFCs (hydrofluorocarbons) — HFCs do not deplete ozone but are potent greenhouse gases; aims to avoid up to 0.5 °C warming by 2100 and cut HFC use by over 80% in 30 years |
Dobson Unit (DU) — the standard measure of ozone column thickness; normal ozone ~300 DU; Antarctic ozone hole values drop below 220 DU.
Greenhouse Gases and Global Warming
| Gas | Formula | Main Sources | GWP (100-year, relative to CO₂) |
|---|---|---|---|
| Carbon Dioxide | CO₂ | Fossil fuel combustion, deforestation, cement production | 1 (reference) |
| Methane | CH₄ | Rice paddies, livestock (enteric fermentation), wetlands, landfills, natural gas leaks | ~30 |
| Nitrous Oxide | N₂O | Fertiliser use, biomass burning, industrial processes | ~273 |
| HFCs | Various | Air conditioning, refrigeration (replacements for CFCs) | 1,530–14,600 (varies by compound) |
| Water vapour | H₂O | Evaporation — most abundant GHG by volume but not directly controlled by human emissions | Not assigned a GWP |
GWP values from IPCC Sixth Assessment Report (AR6, 2021).
Greenhouse effect is a natural phenomenon essential for life — without it, Earth's average temperature would be about –18 °C instead of ~15 °C. The problem is the enhanced greenhouse effect caused by rising concentrations of CO₂, CH₄, and other GHGs due to human activities.
Acid Rain
| Aspect | Detail |
|---|---|
| Cause | Burning of fossil fuels releases SO₂ (sulphur dioxide) and NOₓ (nitrogen oxides); these react with atmospheric moisture to form sulphuric acid (H₂SO₄) and nitric acid (HNO₃) |
| pH threshold | Normal rain is slightly acidic (~pH 5.6 due to dissolved CO₂); acid rain has pH below 5.6 |
| Effects on buildings | Corrodes limestone and marble — CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂; gypsum (CaSO₄) swells and flakes off, damaging structures |
| Marble cancer | The corrosion of the Taj Mahal's marble by acid rain (from Mathura refinery emissions and vehicular pollution) — referred to as "marble cancer" |
| Effects on ecosystems | Acidifies lakes and rivers (kills fish and aquatic organisms), damages forest foliage, leaches nutrients from soil |
| Mitigation | Use of low-sulphur fuels, flue-gas desulphurisation (scrubbers), catalytic converters in vehicles, shift to renewable energy |
Water Pollution Chemistry
| Concept | Detail |
|---|---|
| BOD (Biochemical Oxygen Demand) | Amount of dissolved oxygen consumed by microorganisms to decompose organic matter in water; high BOD = heavily polluted water (organic waste depletes oxygen) |
| COD (Chemical Oxygen Demand) | Total oxygen required to chemically oxidise all organic matter (biodegradable + non-biodegradable); COD is always equal to or greater than BOD |
| Eutrophication | Excessive enrichment of water bodies with nitrogen and phosphorus (from fertiliser runoff, detergents) → algal blooms → algae die and decompose → oxygen depletion → dead zones where aquatic life cannot survive |
| Heavy metal contamination | Lead (Pb), mercury (Hg), cadmium (Cd), arsenic (As) enter water from industrial effluents and mining; bioaccumulation and biomagnification concentrate toxins up the food chain |
| Minamata disease | Mercury poisoning from contaminated fish — first identified in Minamata, Japan (1956); led to global mercury regulation (Minamata Convention, 2013) |
UPSC Relevance
Prelims focus areas: Carbon's tetravalency and catenation, saturated vs unsaturated hydrocarbons, functional groups (hydroxyl, carboxyl, amine, ester), thermoplastics vs thermosetting plastics, recycling codes, Montreal Protocol vs Kigali Amendment, GWP of greenhouse gases, BOD vs COD, acid rain and marble cancer, biomolecules (carbohydrates, proteins, lipids, nucleic acids), microplastics definition and sources.
Mains and essay links (GS-3): Single-use plastic ban and EPR framework for waste management policy, microplastics as an emerging environmental and health concern, bioplastics (PLA, PHA) as sustainable alternatives, ozone layer recovery as a multilateral success story, greenhouse gas emissions and India's climate commitments, eutrophication and river pollution (Namami Gange).
Key terms to remember: Catenation, tetravalency, monomer, polymer, thermoplastic, thermosetting, CFC, HFC, ODS, Dobson Unit, BOD, COD, eutrophication, biomagnification, marble cancer, microplastics, nanoplastics, EPR (Extended Producer Responsibility), PLA, PHA, bioplastics, enzymes, amino acids, nucleotides.
Vocabulary
Polymer
- Pronunciation: /ˈpɒlɪmər/
- Definition: A large molecule (macromolecule) composed of many repeating structural units called monomers, bonded together by covalent chemical bonds.
- Origin: From Greek polus (many) + meros (part); the term was coined by Swedish chemist Jons Jacob Berzelius in 1833.
Monomer
- Pronunciation: /ˈmɒnəmər/
- Definition: A relatively small molecule that can bond chemically with other identical or similar molecules to form a polymer chain.
- Origin: From Greek monos (single) + meros (part); first recorded in English in the 1910s.
Hydrocarbon
- Pronunciation: /ˌhaɪdrəˈkɑːrbən/
- Definition: An organic compound consisting entirely of hydrogen and carbon atoms, occurring naturally in petroleum, natural gas, and coal.
- Origin: A compound of hydrogen (from Greek hydro-, water + -gen, producing) + carbon (from Latin carbō, charcoal); the term dates from 1800.
Key Terms
Polymerisation
- Pronunciation: /pəˌlɪməraɪˈzeɪʃən/
- Definition: A chemical process in which small monomer molecules react together to form long polymer chains or three-dimensional networks, occurring by either addition (chain-growth) polymerisation -- where monomers add directly without loss of any atoms (e.g., polyethylene from ethylene, PVC from vinyl chloride) -- or condensation (step-growth) polymerisation -- where monomers join with the loss of a small molecule like water (e.g., nylon, polyester, Bakelite). Polymers can be natural (proteins, starch, cellulose, natural rubber, DNA) or synthetic (plastics, synthetic fibres, synthetic rubber).
- Context: The modern understanding of polymer science was advanced by German chemist Hermann Staudinger in the 1920s (Nobel Prize in Chemistry, 1953, for demonstrating that polymers are long-chain molecules). Key classification: thermoplastics (can be remoulded on heating -- polyethylene, PVC, nylon, PET) vs thermosetting plastics (cannot be remoulded once set -- Bakelite, melamine, epoxy). India generates approximately 62 million tonnes of solid waste annually, of which ~3.4 million tonnes is plastic waste. On 1 July 2022, India banned 19 identified single-use plastic (SUP) items. Extended Producer Responsibility (EPR) guidelines (February 2022) require producers to collect and recycle packaging waste. Microplastics (plastic particles <5 mm) have been detected in human blood, placenta, and drinking water, emerging as a major environmental and health concern.
- UPSC Relevance: GS3 (General Science / Environment). Prelims tests thermoplastics vs thermosetting plastics (Bakelite -- first fully synthetic plastic, 1907), recycling codes (PET=1, HDPE=2, PVC=3, LDPE=4, PP=5, PS=6), biodegradable vs non-biodegradable materials, and rubber vulcanisation (Charles Goodyear, 1839). Know India's SUP ban (1 July 2022, 19 items), EPR guidelines (February 2022), and bioplastics (PLA from corn starch, PHA from bacterial fermentation) as sustainable alternatives. Mains frequently asks about microplastics as an emerging environmental and health concern, India's Plastic Waste Management Rules, circular economy, and the tension between plastic convenience and environmental damage.
Green Chemistry
- Pronunciation: /ɡriːn ˈkɛmɪstri/
- Definition: The design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances across the entire lifecycle of a product -- from raw material sourcing through manufacturing, use, and disposal. It is guided by twelve core principles including prevention of waste (better to prevent than treat), atom economy (maximise incorporation of all atoms into final product), use of renewable feedstocks, design for energy efficiency, and design for degradation (products should break down harmlessly after use).
- Context: The term was coined in 1991 by Paul Anastas while working at the U.S. Environmental Protection Agency. Anastas and John Warner formalised the twelve principles in their 1998 book Green Chemistry: Theory and Practice. Green chemistry represents a shift from "end-of-pipe" pollution treatment to pollution prevention at source. Examples: replacing toxic organic solvents with water or supercritical CO2, using catalysts instead of stoichiometric reagents, developing biodegradable pesticides, and producing bioplastics from renewable sources. India's Chemical and Petrochemical Department promotes green chemistry through research funding and industrial partnerships. The concept aligns with India's Lifestyle for Environment (LiFE) mission and circular economy goals.
- UPSC Relevance: GS3 (Science & Technology / Environment). Prelims may test the concept definition, that it was formalised by Paul Anastas (1991), and key principles (prevention over treatment, atom economy, use of renewable feedstocks). Mains connects green chemistry to sustainable development, circular economy (reducing waste at source), India's climate commitments (NDCs, Net Zero by 2070), and pollution prevention. Links to ozone layer protection (Montreal Protocol 1987, Kigali Amendment 2016 for HFC phase-down -- India committed to 80% HFC reduction by 2047), greenhouse gas mitigation, and India's BioE3 Policy (2024) promoting bio-based chemical alternatives. A useful conceptual framework for any GS3 answer on sustainable industrial development.
Sources: NCERT Class 10 Science (Chapter 4 — Carbon and its Compounds), NCERT Class 12 Chemistry (Chapter 13 — Amines), US EPA (Understanding Global Warming Potentials; Montreal Protocol; Microplastics Research), IPCC AR6 (GWP values, 2021), PIB (Single-use Plastic Ban, 1 July 2022; EPR Guidelines, 16 February 2022), UNEP Ozone Secretariat (Montreal Protocol, Kigali Amendment), UNEP (Microplastics), Leslie et al. (2022) — Environment International (Microplastics in human blood, VU Amsterdam), NOAA (Eutrophication definition; Microplastics), Britannica (Biomolecules), Wikipedia (Acid Rain, Ozone-oxygen cycle, Resin identification code, Bioplastics).
