Chemistry Guru – Condensed Exam Notes

Experimental Chemistry

  • Measurement apparatus
    • Mass: electronic balance
    • Volume (accurate): burette ±0.05 cm3\pm 0.05\ \text{cm}^3, pipette (fixed vol.)
    • Gas: gas syringe
  • Gas collection
    • Insoluble gases → displacement of water
    • M<em>r>30M<em>r>30 & dense → downward delivery • Mr<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=Z= protons, A−Z=A-Z= neutrons, electrons = protons (atom)
  • Ions: loss → cation, gain → anion (achieve noble-gas config.)
  • Isotopes: same ZZ, 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+1, 2 +2+2, 3 +3+3, 17 −1-1, 16 −2-2, 15 −3-3; NH<em>4+<em>4^+, OH$^-,NO, NO3^-,SO, SO4^{2-},CO, CO3^{2-}
  • Ionic formula: cross charges (simplify) e.g. Al$^{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^+inwater;Alkali:releasesin water; Alkali: releasesOH^- in water
  • Key reactions
    • Metal + acid → salt + H$2$ • Acid + base/alkali → salt + H$2$O
    • Acid + carbonate → salt + H$2$O + CO$2$
    • Alkali + NH$4^+$ salt → salt + NH$3$ + H$_2$O
  • pH scale 0–14: [H^+]\uparrow → pH↓; UI colours red (0) to violet (14)
  • Indicators: methyl orange (red→yellow pH3−5),phenolphthalein(colourless→pink3-5), phenolphthalein (colourless→pinkpH 8-10)
  • Soil too acidic → add CaO or Ca(OH)$_2$ (liming)
  • Oxides
    • Basic: metal oxides
    • Acidic: non-metal oxides
    • Amphoteric: Al$2$O$3$, ZnO, PbO
    • Neutral: CO, NO

Qualitative Analysis

  • Gas tests
    • H$2$: lighted splint → ‘pop’ • O$2$: glowing splint relights
    • CO$2$: turns limewater milky • NH$3$: 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$_2$O (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 O$2$ + H$2$O; 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, Al$2$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 Cl$2$/Br$2$ (UV)
Alkenes CnH{2n} (unsaturated, C=C)
  • 2–3 C: ethene, propene
  • More reactive: combustion (sooty), addition
    • +H$2$ (200 °C, Ni) → alkane (margarine) • +Br$2$ (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
    • NO$x$: lightning, engines • SO$2$: volcanoes, burning sulfur fuels
    • Unburnt hydrocarbons, O$3$, CH$4$
  • Effects
    • CO: toxic, blocks O2 transport • NO$2$, SO$2$: acid rain → corrodes CaCO$3$, harms lakes/forests
  • Carbon cycle: photosynthesis removes CO$2$; respiration & combustion add; keeps \text{[CO}2]$$ ~ constant
  • Greenhouse gases: CO$2$, CH$4$ trap heat → global warming; consequences: extreme weather, melting ice, sea-level rise