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:

  1. Incoming solar radiation reaches atmosphere; part reflected to space.

  2. Remainder absorbed by land & oceans → warms Earth.

  3. Earth radiates infrared (heat) back to space.

  4. Portion trapped by GHGs → maintains life-supporting temperature.

  5. Human activities (burning fossil fuels, agriculture, land clearing) elevate GHG levels.

  6. 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: $\text{C} + \text{O}<em>2 \rightarrow \text{CO}</em>2$

  • 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: $\text{SO}<em>2 + \text{H}</em>2\text{O} + \tfrac12\text{O}<em>2 \rightarrow \text{H}</em>2\text{SO}_4$ → 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 $\text{N}<em>2 + \text{O}</em>2$ reaction) & during lightning.

• Form nitric acid in air: $2\text{NO}<em>2 + \text{H}</em>2\text{O} \rightarrow \text{HNO}<em>3 + \text{HNO}</em>2$ → acid rain.

• Cause lung damage, eye/skin irritation.

Acid Rain

• Cause: $\text{SO}<em>2$ & $\text{NO}</em>x$ converting to $\text{H}<em>2\text{SO}</em>4$ & $\text{HNO}_3$ 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 $\text{CO}$, $\text{SO}<em>2$, $\text{NO}</em>x$.

• 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 → $\text{Cl} + \text{O}<em>3 \rightarrow \text{ClO} + \text{O}</em>2$ (repeat cycle) → thins ozone layer.

• Consequence: greater UV penetration → higher skin cancer, cataract & skin disease risks.

Measures to Reduce Air Pollution

1. Flue-gas desulfurisation: pass $\text{SO}<em>2$-laden gases over powdered $\text{CaCO}</em>3$ → $\text{CaSO}<em>4 + \text{CO}</em>2$.

2. Catalytic converters in vehicles: $2\text{CO} \rightarrow \text{CO}<em>2$; $2\text{NO} \rightarrow \text{N}</em>2 + \text{O}_2$.

3. Promote public transport & carpooling to cut fuel use.

4. Transition to clean energy (solar, wind, tidal).

5. Replace CFCs with ozone-friendly alternatives.

6. 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.

  1. Identify elements: Na (valency $1$), O (valency $2$).

  2. Swap valencies → $\text{Na}<em>2\text{O}</em>1$ → 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 → $\text{Cu}^{2+}$ & $\text{NO}<em>3^-$; formula $\text{Cu}(\text{NO}</em>3)_2$.

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 $\text{FeCl}<em>2$ + $\text{H}</em>2$.

  • 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: $\text{metal} + \text{H}<em>2\text{O} \rightarrow \text{metal hydroxide} + \text{H}</em>2$ (only very reactive metals).

• With steam: $\text{metal} + \text{H}<em>2\text{O (g)} \rightarrow \text{metal oxide} + \text{H}</em>2$ (moderately reactive metals).

• With acids (e.g., HCl): see general equation above.

• Notes:

  • Aluminium forms protective $\text{Al}<em>2\text{O}</em>3$ 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: $\text{N}<em>2 = 78\% ,\ \text{O}</em>2 = 21\% ,\ \text{Ar} \text{+ inert} = 0.96\% ,\ \text{CO}_2 = 0.04\%$.

• Sea level rise (Mauritius/Rodrigues): $4\,\text{mm yr}^{-1}$ / $6\,\text{mm yr}^{-1}$.

• Desulfurisation: $\text{CaCO}<em>3 + \text{SO}</em>2 + \tfrac12\text{O}<em>2 \rightarrow \text{CaSO}</em>4 + \text{CO}_2$.

• Catalytic converter (simplified): $2\text{CO} + 2\text{NO} \rightarrow \text{N}<em>2 + 2\text{CO}</em>2$.

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.