UGC NET Environmental Science Unit-II: Environmental Chemistry Flashcards

24 sample cards from the Unit-II: Environmental Chemistry deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. Describe the main reservoirs and fluxes of the carbon cycle.

   Carbon moves among the atmosphere (CO₂), oceans (dissolved CO₂/carbonates), biosphere (organic matter), and lithosphere (fossil fuels, carbonate rocks). Photosynthesis fixes CO₂; respiration, decomposition, and combustion release it.

2. What is distinctive about the phosphorus cycle compared with the nitrogen and carbon cycles?

   The phosphorus cycle is a sedimentary cycle with no significant gaseous (atmospheric) phase. P is released by weathering of rocks (phosphate), cycled through organisms, and lost to ocean sediments; it is often the limiting nutrient in freshwater.

3. Outline the sulphur biogeochemical cycle.

   Sulphur cycles among rocks/sediments, water, atmosphere, and organisms. Key transformations: mineralization of organic S to H₂S/SO₄²⁻, oxidation to sulphate, reduction (sulphate-reducing bacteria → H₂S), and atmospheric SO₂/sulphate from volcanism and fossil fuel burning.

4. How are pesticides classified based on chemical nature? Give examples.

   Major classes: organochlorines (e.g. DDT, endosulfan), organophosphates (e.g. malathion, parathion), carbamates (e.g. carbaryl), and pyrethroids (e.g. permethrin). They are also classed by target as insecticides, herbicides, fungicides, rodenticides.

5. Why are organochlorine pesticides like DDT especially harmful in the environment?

   They are persistent (resist degradation), lipophilic, and bioaccumulate and biomagnify up food chains, causing toxic effects (e.g. eggshell thinning in birds) and long-term ecosystem contamination.

6. What is the biochemical toxic effect of mercury (Hg), and what is its most toxic form?

   Mercury binds to sulfhydryl (−SH) groups of proteins/enzymes, damaging the nervous system and kidneys. Methylmercury (CH₃Hg⁺) is the most toxic, highly bioaccumulative form, causing Minamata disease.

7. Describe the toxic effects of lead (Pb) and cadmium (Cd) on humans.

   Lead inhibits heme synthesis enzymes (e.g. ALA dehydratase), causing anemia and neurotoxicity (especially in children). Cadmium damages kidneys and bones, causing Itai-itai disease, and disrupts Zn/Ca-dependent enzymes.

8. How does chromium toxicity depend on its oxidation state?

   Cr(III) is an essential trace nutrient and relatively non-toxic, whereas Cr(VI) (chromate/dichromate) is highly toxic, mutagenic, and carcinogenic, being readily absorbed and a strong oxidant inside cells.

9. What are the toxicological concerns of the metalloids arsenic (As) and selenium (Se)?

   Arsenic inhibits cellular respiration enzymes and is a carcinogen (causes skin lesions, cancers; arsenicosis from contaminated groundwater). Selenium is essential in trace amounts but toxic in excess (selenosis), with a narrow safe-to-toxic range.

10. What is PAN, how is it formed, and why is it significant?

    PAN (peroxyacetyl nitrate, CH₃COOONO₂) is a secondary pollutant formed in photochemical smog from acetyl radicals + NO₂. It is a powerful eye irritant, phytotoxic to plants, and a reservoir that transports NOx over long distances.

11. Why are carbon monoxide (CO) and ground-level ozone (O₃) harmful pollutants?

    CO binds hemoglobin ~200× more strongly than O₂, forming carboxyhemoglobin and causing tissue hypoxia. Ground-level O₃ is a strong oxidant that irritates the respiratory tract, damages lungs, and harms vegetation.

12. What are VOCs and POPs in the context of air pollution?

    VOCs (volatile organic compounds, e.g. benzene, toluene) are organics that readily evaporate and serve as smog/ozone precursors. POPs (persistent organic pollutants, e.g. PCBs, dioxins, DDT) resist degradation, bioaccumulate, and travel long distances (Stockholm Convention).

13. Name important carcinogens found in air and a common source of each.

    Benzene (vehicle exhaust, petrol), benzo[a]pyrene and other PAHs (incomplete combustion, smoke), formaldehyde (combustion, building materials), asbestos fibers (insulation), and 1,3-butadiene (vehicle exhaust).

14. What is titrimetry (volumetric analysis) and what defines the equivalence point?

    Titrimetry determines an analyte's concentration by reacting it with a standard solution of known concentration until the reaction is complete. The equivalence point is when stoichiometrically equivalent amounts have reacted; the endpoint (indicator change) signals it.

15. What is gravimetric analysis and on what principle is the result calculated?

    Gravimetry quantifies an analyte by converting it to a pure, weighable solid (usually a precipitate) and measuring its mass. The analyte amount is calculated from the mass of product using stoichiometry and the gravimetric factor.

16. What does a bomb calorimeter measure and under what conditions?

    A bomb calorimeter measures the heat of combustion (calorific value) of a sample at constant volume, giving ΔU (internal energy change). Sample is burned in excess O₂ in a sealed bomb immersed in water; heat released raises the water temperature.

17. State the basic principle of chromatography and name the two phases involved.

    Chromatography separates components of a mixture based on their differential distribution (partitioning/adsorption) between a stationary phase and a moving mobile phase; components with greater affinity for the mobile phase move faster.

18. What is the principle of flame photometry and which elements is it best suited for?

    Flame photometry (flame emission spectroscopy) measures the intensity of light emitted by atoms excited in a flame, which is proportional to concentration. It is best for easily excited alkali and alkaline-earth metals: Na, K, Li, Ca, Ba.

19. State the principle of spectrophotometry and the law it relies on.

    Spectrophotometry measures absorption (or transmission) of light by a solution at a specific wavelength. It relies on the Beer–Lambert law: A = εcl, where absorbance is proportional to concentration (c), path length (l), and molar absorptivity (ε).

20. What is electrophoresis and what governs the separation of species?

    Electrophoresis separates charged molecules (ions, proteins, nucleic acids) by their migration in an electric field through a medium (e.g. gel). Separation depends on charge, size, and shape — smaller, more highly charged molecules move faster.

21. What do XRF and XRD analyze, and how do their purposes differ?

    XRF (X-ray fluorescence) identifies and quantifies elemental composition by measuring characteristic X-rays emitted after excitation. XRD (X-ray diffraction) determines crystalline structure and mineral phases using Bragg's law (nλ = 2d sinθ).

22. What structural information do NMR and FTIR spectroscopy provide?

    NMR (nuclear magnetic resonance) reveals the molecular/structural environment of nuclei (e.g. ¹H, ¹³C) — connectivity and number of H/C atoms. FTIR (Fourier-transform infrared) identifies functional groups by their characteristic vibrational absorption bands.

23. What does GC-MS do, and why is it powerful for environmental analysis?

    GC-MS couples gas chromatography (separates volatile/semi-volatile compounds) with mass spectrometry (identifies/quantifies by mass-to-charge ratio). It enables sensitive identification and quantification of trace organic pollutants like pesticides, PAHs, and VOCs.

24. Compare SEM and TEM in terms of imaging and resolution.

    SEM (scanning electron microscope) scans the surface with an electron beam to give 3D-like surface/topographic images at moderate resolution. TEM (transmission electron microscope) passes electrons through ultrathin samples for very high-resolution internal/structural images at near-atomic scale.

What this deck covers

Unit-II: Environmental Chemistry flashcards FAQ