Chemistry Guru – Condensed Exam Notes

Experimental Chemistry

• Measurement apparatus
  • Mass: electronic balance
  • Volume (accurate): burette $\pm 0.05\ \text{cm}^3$, pipette (fixed vol.)
  • Gas: gas syringe
• Gas collection
  • Insoluble gases → displacement of water
  • $M<em>r>30$ & dense → downward delivery • $M</em>r<30$ & light → upward delivery
• Separation / purification
  • Solid–solid → choose solvent → filtration (+ evaporation / crystallisation)
  • Solid–liquid → filtration
  • Liquid–liquid (miscible) → fractional distillation
  • Chromatography: compare spots; start line in pencil; solvent below line
• Purity criteria
  • Pure: sharp m.p./b.p.; impurities ↓m.p., ↑b.p.

Particulate Nature of Matter

• Kinetic particle theory: particles in constant random motion
• States & changes
  • Heating: ↑kinetic energy, ↑spacing, ↓attraction (solid→liquid→gas)
  • Cooling: reverse
• Heating/cooling curves: plateaus = change of state (m.p., b.p.)

Atomic Structure

• Sub-particles: proton +1 (1), neutron 0 (1), electron –1 $\tfrac1{1840}$
• Nuclide: $^{A}_{Z}X$ ; $Z=$ protons, $A-Z=$ neutrons, electrons = protons (atom)
• Ions: loss → cation, gain → anion (achieve noble-gas config.)
• Isotopes: same $Z$, different neutrons; same chem., diff. phys.

Chemical Bonding & Structure

• Ionic bonding
  • Metal → non-metal; e⁻ transfer; strong electrostatic forces in giant lattice
  • Properties: high m.p./b.p., soluble in water, conduct when molten/aq (mobile ions)
• Covalent bonding
  • Non-metals share e⁻; single/double/triple bonds
  • Simple molecules: low m.p./b.p., non-conductors (no mobile charges)
• Drawing tips: keep 8/2 e⁻ rule; different symbols for transferred e⁻
• Elements vs compounds vs mixtures
  • Element → 1 type of atom
  • Compound → fixed ratio, chem. bonded
  • Mixture → phys. combined; separated by physical methods
• Metals
  • High m.p./b.p., malleable (layers slide), good conductors
  • Alloy = mixture of metal + element; irregular layers → harder/stronger

Formulae, Equations & Moles

• Common ion charges: Group 1 $+1$, 2 $+2$, 3 $+3$, 17 $-1$, 16 $-2$, 15 $-3$; NH$<em>4^+$, OH$^-$, NO$3^-$, SO$4^{2-}$, CO$3^{2-}
• Ionic formula: cross charges (simplify) e.g. Al^{3+}$+ O$^{2-}$→ Al$2$O$3
• Balancing: adjust coefficients only; include (s,l,g,aq)
• Ionic equations: split aqueous ions; cancel spectators; universal neutralisation H^+ + OH^- \rightarrow H_2O
• Mole relation: \text{mass}=\text{mol}\times\text{Mr}$;$\text{mol}=\dfrac{\text{mass}}{\text{Mr}}

Acid–Base Chemistry

• Acid: releases H^+$in water; Alkali: releases$OH^- in water
• Key reactions
  • Metal + acid → salt + H2 • Acid + base/alkali → salt + H2O
  • Acid + carbonate → salt + H2$O + CO$2
  • Alkali + NH4^+$salt → salt + NH$3$+ H$_2O
• pH scale 0–14: [H^+]\uparrow → pH↓; UI colours red (0) to violet (14)
• Indicators: methyl orange (red→yellow pH$3-5), phenolphthalein (colourless→pink$pH 8-10)
• Soil too acidic → add CaO or Ca(OH)_2 (liming)
• Oxides
  • Basic: metal oxides
  • Acidic: non-metal oxides
  • Amphoteric: Al2$O$3, ZnO, PbO
  • Neutral: CO, NO

Qualitative Analysis

• Gas tests
  • H2: lighted splint → ‘pop’ • O2: glowing splint relights
  • CO2: turns limewater milky • NH3: damp red litmus → blue

Periodic Table & Reactivity

• Arrangement: increasing Z; groups = valence e⁻; periods = shells
• Metallic character ↑ down group, ↓ across period
• Group 1: soft, low d, m.p.↓ down group, react vigorously with H_2O (Li<Na<K)
• Group 17: coloured diatomic gases→liquid→solid; m.p./b.p.↑ down group; reactivity ↓; displacement: more reactive halogen replaces less reactive halide
• Group 18: noble gases; inert (full valence shell)
• Reactivity series: K>Na>Ca>Mg>Al>(C)>Zn>Fe>Pb>(H)>Cu>Ag>Au
  • Above H: react with acids (except Pb slow)
  • Above C: extract by electrolysis; below C by reduction
• Rusting: needs O2$+ H$2O; prevent by barrier coating or sacrificial Zn/Mg

Organic Chemistry

Crude Oil & Fuels

• Crude oil = hydrocarbon mixture; fractional distillation separates by b.p.
  • Top: petroleum gas, petrol; Bottom: lubricating oil, bitumen
• Cracking (600 °C, Al2$O$3$/SiO$2$): long alkanes → shorter alkanes + alkenes + H$2; meets demand
• Bioethanol: fermentation of sugarcane; CO_2 absorbed during growth offsets combustion

Homologous Series

• Features: same functional group, general formula, similar chem., gradation in phys.
• Prefixes: meth-1, eth-2, prop-3, but-4

Alkanes CnH{2n+2} (saturated)

• 1–4 C: methane, ethane, propane, butane
• Properties: low m.p./b.p.; m.p./b.p.↑ with size; poor conductors
• Reactions: combustion; substitution with Cl2$/Br$2 (UV)

Alkenes CnH{2n} (unsaturated, C=C)

• 2–3 C: ethene, propene
• More reactive: combustion (sooty), addition
  • +H2 (200 °C, Ni) → alkane (margarine) • +Br2 (aq) decolourises → test for C=C
  • Polymerisation: n\,CH2=CH2 \rightarrow (–CH2CH2–)_n poly(ethene)

Plastics & Recycling

• Non-biodegradable → land, air, water pollution
• Recycling
  • Physical: melt & remould into pellets
  • Chemical: crack into fuels/monomers

Air Quality & Environment

• Dry air: 78\%$N$2$,$21\%$O$2$,$0.97\% Ar & other noble gases, 0.03\%$CO$_2
• Pollutants & sources
  • CO: incomplete combustion
  • NOx: lightning, engines • SO2: volcanoes, burning sulfur fuels
  • Unburnt hydrocarbons, O3$, CH$4
• Effects
  • CO: toxic, blocks O2 transport • NO2$, SO$2$: acid rain → corrodes CaCO$3, harms lakes/forests
• Carbon cycle: photosynthesis removes CO2; respiration & combustion add; keeps \text{[CO}2] ~ constant
• Greenhouse gases: CO2$, CH$4$$ trap heat → global warming; consequences: extreme weather, melting ice, sea-level rise