Overview
This lecture covers key concepts and experiments from AQA Chemistry Paper 2 Topics 6–10, including rates of reaction, organic chemistry, chemical analysis, atmospheric chemistry, and using resources, with notes on both combined and triple science content.
Rates of Reaction
- Rate of reaction = change in quantity (mass/volume) ÷ time.
- Rate experiments: measure time for a reaction to obscure a cross or collect gas volume.
- Rate is higher with increased concentration, pressure, surface area, temperature, or use of a catalyst.
- Catalysts lower activation energy and are not consumed.
- Graphs: steep curve leveling off; use tangents for rate at a specific time.
Reversible Reactions & Equilibrium
- Reversible reactions: products can revert to reactants (e.g., Haber process).
- In a closed system, equilibrium is reached when forward/reverse rates are equal.
- Le Chatelier’s Principle: system counteracts changes in pressure, concentration, or temperature.
- Increasing pressure favors side with fewer moles of gas; increasing temperature favors endothermic direction.
Organic Chemistry (C7)
- Organic compounds: carbon-based molecules (mainly hydrocarbons).
- Alkanes: single bonds, formula CnH2n+2, named by chain length (meth-, eth-, prop-, etc.).
- Fractional distillation separates crude oil by boiling points.
- Shorter alkanes: lower boiling points, more flammable, less viscous; long alkanes: opposite.
- Alkenes: unsaturated hydrocarbons with double bonds (C=C), test with bromine water (orange to colorless).
- Cracking: breaks long alkanes into shorter alkanes and alkenes, using heat and/or catalysts.
Polymers & Triple Science Organic
- Alkenes form plastics/polymers through addition polymerization (repeating units).
- Condensation polymerization joins two different monomers, releasing water (e.g., polyesters).
- Amino acids polymerize to make proteins; DNA is a double helix of nucleotide polymers.
- Natural polymers: starch (from glucose), cellulose (from beta glucose), proteins (from amino acids).
Chemical Analysis (C8)
- Pure substances have specific melting/boiling points.
- Formulations: designed mixtures with fixed amounts (e.g., paint, fuel).
- Chromatography separates mixtures; calculate Rf value = distance moved by spot ÷ distance moved by solvent.
- Gas tests: hydrogen (squeaky pop), oxygen (relights splint), carbon dioxide (limewater cloudy), chlorine (bleaches litmus).
- Flame tests: lithium (crimson), sodium (yellow), potassium (lilac), calcium (orange-red), copper (green).
- Sodium hydroxide test: white (aluminium dissolves in excess, calcium, magnesium), blue (copper), green (Fe2+), brown (Fe3+).
- Anion tests: carbonates (CO2 with acid), halides (silver nitrate: Cl– white, Br– cream, I– yellow), sulfates (white precipitate with barium chloride).
- Instrumental analysis (e.g., flame emission spectroscopy) is more accurate and sensitive.
Atmospheric Chemistry (C9)
- Early atmosphere: mainly nitrogen and CO2, little/no oxygen.
- Greenhouse effect: water vapor, CO2, methane trap heat; essential for life, but rising CO2 increases global warming.
- Pollutants: carbon monoxide (toxic), sulfur dioxide (acid rain), nitrogen oxides (breathing issues), particulates (health risks).
Using Resources (C10)
- Sustainable resource use meets current needs without harming future generations.
- Potable water: safe to drink, low salt/microbes, treated by filtration and sterilization.
- Desalination for seawater—energy intensive.
- Waste water treated by filtration, sedimentation, and aerobic/anaerobic processes.
- Metals extracted by mining, electrolysis, displacement, phytomining (plants), or bioleaching (bacteria).
- Life Cycle Assessment evaluates environmental impact at all stages (extraction, use, disposal).
- Corrosion: metals (e.g., iron rusts) destroyed by chemical reactions; galvanizing/protective coatings prevent rust.
- Alloys: mixtures of metals, stronger than pure metals (e.g., bronze, brass, steel, stainless steel).
- Glass, ceramics, composites, and polymers (thermosoftening vs. thermosetting) have specific properties for use.
- Haber process: makes ammonia (NH3) for fertilizers using N2 and H2 over a catalyst at 450°C, 200 atm.
- NPK fertilizers provide nitrogen, phosphorus, and potassium; phosphate rock treated with acid before use.
Key Terms & Definitions
- Rate of Reaction — How quickly reactants are used/products formed per unit time.
- Equilibrium — Point where forward and reverse reaction rates are equal in a closed system.
- Le Chatelier’s Principle — System shifts to oppose imposed changes.
- Alkane — Saturated hydrocarbon (single bonds), formula CnH2n+2.
- Alkene — Unsaturated hydrocarbon (contains C=C double bond).
- Polymer — Large molecule from many repeating monomers.
- Rf Value — Ratio of distance moved by substance to solvent in chromatography.
- Greenhouse Gas — Gases that trap heat in the atmosphere (CO2, methane, water vapor).
- Potable Water — Water safe for drinking.
- Corrosion — Gradual destruction of metals by chemical processes.
- Alloy — Mixture of metals or metals with other elements.
Action Items / Next Steps
- Review required practical experiments for each topic.
- Practice calculations for rates, Rf values, and ionic equations.
- Memorize key tests for gases, ions, and metals.
- Complete any assigned textbook questions or revision worksheets on Paper 2 topics.