Atmosphere & Environment, Chemical Language and Metal Reactivity – Comprehensive Study Notes
Composition of Air
Atmosphere = layer of air surrounding Earth; indispensable for life.
Air is a mixture; major to minor gases (clean, dry sample):
\text{N}_2: 78\%
\text{O}_2: 21\%
\text{CO}_2: 0.04\%
Inert gases (mainly Ar with He, Ne): 0.96\%
Water vapour content is variable (location & day-to-day).
Greenhouse Gases & Greenhouse Effect
Greenhouse = glass structure that traps solar energy → warm interior (analogy for atmosphere).
Main greenhouse gases (GHGs):
Carbon dioxide (\text{CO}_2)
Methane (\text{CH}_4)
Steps of natural/ enhanced greenhouse process:
Incoming solar radiation reaches atmosphere; part reflected to space.
Remainder absorbed by land & oceans → warms Earth.
Earth radiates infrared (heat) back to space.
Portion trapped by GHGs → maintains life-supporting temperature.
Human activities (burning fossil fuels, agriculture, land clearing) elevate GHG levels.
Extra trapping → average global temperature rises (global warming).
Global Warming
Definition: long-term increase in Earth’s average surface temperature caused by rising GHG concentrations.
Sources of key GHGs:
\text{CO}_2: combustion of fossil fuels (power plants, vehicle exhausts); deforestation reduces uptake.
\text{CH}_4: released by cattle, landfills, decomposition of biomass.
Observed impacts (Mauritius examples, IPCC AR6):
Relative sea-level rise: 4\,\text{mm yr}^{-1} (Mauritius), 6\,\text{mm yr}^{-1} (Rodrigues).
Severe coral bleaching & coral abundance decline.
More flash floods (warmer air holds more \text{H}_2\text{O} vapour → greater precipitation).
Warmer oceans favour cyclone formation/intensification.
Consequences list:
Coral bleaching
Melting glaciers, rising sea level, flooding
More frequent cyclones, droughts
Extinction risks for flora & fauna
Combating Climate Change
Overarching aim: cut GHG & pollutant emissions.
Practical measures (Table 3):
Save electricity: use energy-efficient bulbs.
Plant trees (enhance \text{CO}_2 uptake via photosynthesis).
Employ non-polluting energy: solar, wind, tidal, hydro.
Use public transport, carpool.
Recycle plastics.
Burn fewer fossil fuels overall.
Air Pollution
Definition: contamination of air altering its natural characteristics; harms living & non-living entities.
Air pollutants studied: Carbon monoxide, Sulfur dioxide, Oxides of nitrogen, Smoke, CFCs.
Carbon Monoxide (CO)
Formation: incomplete combustion of carbon-containing fuels.
Complete combustion: \text{C} + \text{O}2 \rightarrow \text{CO}2
Incomplete: \text{C} + \tfrac12\text{O}_2 \rightarrow \text{CO}
Sources: portable kerosene generators in closed rooms, charcoal grills in garages, unventilated gas water heaters, vehicle engines.
Health impacts: colourless, odourless “silent killer”; binds haemoglobin → cuts O₂ transport → headache, nausea, dizziness, unconsciousness, death.
Sulfur Dioxide (SO₂)
Origins: burning sulfur-containing fossil fuels (coal-fired power plants, vehicle exhausts); volcanic eruptions.
Atmospheric reaction: \text{SO}2 + \text{H}2\text{O} + \tfrac12\text{O}2 \rightarrow \text{H}2\text{SO}_4 → dissolves in clouds → acid rain.
Health: respiratory irritation, aggravates asthma/bronchitis; irritates eyes/skin.
Oxides of Nitrogen (NO & NO₂)
Produced in vehicle engines (high T causes \text{N}2 + \text{O}2 reaction) & during lightning.
Form nitric acid in air: 2\text{NO}2 + \text{H}2\text{O} \rightarrow \text{HNO}3 + \text{HNO}2 → acid rain.
Cause lung damage, eye/skin irritation.
Acid Rain
Cause: \text{SO}2 & \text{NO}x converting to \text{H}2\text{SO}4 & \text{HNO}_3 in atmosphere.
Effects: corrodes steel, erodes limestone, acidifies soils & water bodies → ecological harm.
Smoke
Sources: vehicle exhausts, factory chimneys, forest fires, garbage burning, BBQs, cigarettes.
Composition: soot (carbon particulates) + ash; contains \text{CO}, \text{SO}2, \text{NO}x.
Hazards: suffocation (O₂ depletion), lung damage, eye/skin irritation, carbon-monoxide poisoning.
Chlorofluorocarbons (CFCs)
Composition: C, F, Cl atoms.
Uses (historical): refrigerants, air-conditioner coolants, aerosol propellants, cleaning agents.
Ozone depletion mechanism: UV photolysis releases Cl radicals → \text{Cl} + \text{O}3 \rightarrow \text{ClO} + \text{O}2 (repeat cycle) → thins ozone layer.
Consequence: greater UV penetration → higher skin cancer, cataract & skin disease risks.
Measures to Reduce Air Pollution
Flue-gas desulfurisation: pass \text{SO}2-laden gases over powdered \text{CaCO}3 → \text{CaSO}4 + \text{CO}2.
Catalytic converters in vehicles: 2\text{CO} \rightarrow \text{CO}2; 2\text{NO} \rightarrow \text{N}2 + \text{O}_2.
Promote public transport & carpooling to cut fuel use.
Transition to clean energy (solar, wind, tidal).
Replace CFCs with ozone-friendly alternatives.
Avoid open waste burning; maintain vehicles to minimise smoke.
Water Pollution
Occurs when harmful substances enter water bodies.
Anthropogenic sources & effects:
Untreated sewage: pathogenic viruses/bacteria → fish kills, human disease.
Agricultural fertilisers: nutrient runoff → eutrophication (algal bloom → O₂ depletion → aquatic death).
Industrial wastes: heavy metals, detergents, pesticides, acids, dyes → toxicity.
Oil spills: coat & suffocate marine life.
Plastic dumping: ingestion & entanglement hazards.
Prevention:
Treat sewage & industrial effluents.
Apply fertilisers judiciously.
Dispose litter in bins.
Language of Chemistry (Symbols, Valency & Formulae)
Element symbol: 1–2 letters; first capital, second lowercase (e.g. \text{Na},\,\text{Cl}).
Valency = combining power; examples:
\text{H}:1,\ \text{O}:2,\ \text{Al}:3,\ \text{Fe}:2\text{ or }3 etc.
Working out formula example: sodium oxide.
Identify elements: Na (valency 1), O (valency 2).
Swap valencies → \text{Na}2\text{O}1 → simplest ratio \text{Na}_2\text{O}.
Subscript shows number of atoms; absence = 1.
Radicals: group of atoms with overall valency. Common radicals & valencies:
Hydroxide \text{OH}^-: 1
Ammonium \text{NH}_4^+: 1
Nitrate \text{NO}_3^-: 1
Carbonate \text{CO}_3^{2-}: 2
Sulfate \text{SO}_4^{2-}: 2
Example formula with radical: copper(II) nitrate → \text{Cu}^{2+} & \text{NO}3^-; formula \text{Cu}(\text{NO}3)_2.
Chemical Reactions & Equations
Word equation layout: Reactants \rightarrow Products.
Example: iron + sulfur \xrightarrow{\text{heat}} iron(II) sulfide.
Key principles:
Atoms rearrange; mass conserved.
Equations must be balanced by adjusting coefficients only.
Never alter formulas during balancing.
Radicals may be balanced as whole units.
Six-step balancing procedure: write word eqn, convert to formulas, draft chemical eqn, count atoms, add coefficients, re-count & iterate.
Metals & Reactivity Series
Reactions with Dilute Hydrochloric Acid
General reaction: \text{metal} + 2\text{HCl} \rightarrow \text{metal chloride} + \text{H}_2 ↑
Observations (bubble rate ∝ reactivity):
Copper: no reaction.
Iron: slow → pale green \text{FeCl}2 + \text{H}2.
Zinc: moderate → colourless \text{ZnCl}_2.
Magnesium: vigorous → colourless \text{MgCl}_2.
Relative reactivity (most → least): Mg > Zn > Fe > Cu.
Full Reactivity Series Mnemonic
(Please) Potassium
(Send) Sodium
(Charlie’s) Calcium
(Monkey) Magnesium
(And) Aluminium
(Zebras) Zinc
(In) Iron
(Lead) Lead
(Cages) Copper
(Securely) Silver
(Guarded) Gold
Reaction Types Summaries
With oxygen: \text{metal} + \text{O}_2 \rightarrow \text{metal oxide} (rate depends on position in series).
With cold water: \text{metal} + \text{H}2\text{O} \rightarrow \text{metal hydroxide} + \text{H}2 (only very reactive metals).
With steam: \text{metal} + \text{H}2\text{O (g)} \rightarrow \text{metal oxide} + \text{H}2 (moderately reactive metals).
With acids (e.g., HCl): see general equation above.
Notes:
Aluminium forms protective \text{Al}2\text{O}3 layer that hinders further reaction.
Lead generates insoluble \text{PbCl}_2, halting acid reaction.
Ethical & Practical Connections
Climate change & pollution mitigation demand collective policy & individual action.
Industrial processes must integrate flue-gas cleaning, catalytic technologies & renewable energy adoption.
Safe domestic practices: adequate ventilation for combustion devices, refrain from indoor charcoal burning.
Material science & extraction rely on reactivity series to select suitable extraction methods.
Key Equations & Data (Compiled)
Greenhouse gas percentages: \text{N}2 = 78\% ,\ \text{O}2 = 21\% ,\ \text{Ar} \text{+ inert} = 0.96\% ,\ \text{CO}_2 = 0.04\%.
Sea level rise (Mauritius/Rodrigues): 4\,\text{mm yr}^{-1} / 6\,\text{mm yr}^{-1}.
Desulfurisation: \text{CaCO}3 + \text{SO}2 + \tfrac12\text{O}2 \rightarrow \text{CaSO}4 + \text{CO}_2.
Catalytic converter (simplified): 2\text{CO} + 2\text{NO} \rightarrow \text{N}2 + 2\text{CO}2.
Rapid-Review Bullet List
Greenhouse gases (CO₂, CH₄) trap heat → global warming.
Anthropogenic activities elevate GHGs; impacts: floods, cyclones, coral bleaching, sea-level rise.
Air pollutants & their major health/environmental effects:
CO: silent killer (Hb binding).
SO₂ & NOₓ: acid rain, respiratory issues.
Smoke: suffocation, particulate damage.
CFCs: ozone depletion, UV health risks.
Pollution control technologies: flue-gas limestone scrubbers, catalytic converters, renewables.
Water pollution pathways: sewage, fertiliser runoff, industry, oil spills, plastics; eutrophication process.
Chemistry language essentials: symbols, valencies, radicals, formula derivation, equation balancing.
Reactivity series guides prediction of metal behaviour with O₂, H₂O, steam & acids; magnesium most reactive among Mg, Zn, Fe, Cu.