Overview
This lecture covered all key content for GCSE Chemistry Paper 2, including required practicals, core theory, calculation skills, and exam tips for both combined and triple science students.
Rates of Reaction & Required Practicals
- Rate of reaction is measured as change in reactant/product over time (e.g. g/s, cm³/s, mol/s).
- Methods include measuring mass loss (using a balance) or gas volume collected (gas syringe or over water).
- Always record time zero and include units in table headers.
- Plot data with line of best fit; use gradient for rate.
- Tangents on curved graphs find instantaneous rate.
- Collision theory: particles must collide with enough (activation) energy.
- Factors affecting rate: pressure, concentration, surface area, temperature, catalyst.
- Required practical: investigate how changing concentration affects rate; identify independent, dependent, and control variables.
- Turbidity (cloudiness) method uses time until cross is obscured.
Reversible Reactions & Equilibrium
- Reversible reactions can go both ways; shown by a double arrow.
- At equilibrium, forward and backward reaction rates are equal, but concentrations are not necessarily equal.
- Le Chatelier’s Principle: System opposes changes by shifting position of equilibrium.
- Changing pressure favors side with fewer gas molecules; changing temperature favors endothermic/exothermic direction accordingly.
- Catalysts increase rate but don’t affect equilibrium position.
Organic Chemistry & Crude Oil
- Crude oil: finite mixture of hydrocarbons from ancient biomass (mainly plankton).
- Hydrocarbons: molecules with only hydrogen and carbon.
- Alkanes: saturated hydrocarbons, general formula CnH2n+2; know methane, ethane, propane, butane.
- Fractional distillation separates hydrocarbons by boiling point into useful fractions.
- Complete combustion produces CO₂ and H₂O; incomplete produces CO, particulates.
- Common pollutants: CO₂ (global warming), CO, SO₂, NOₓ, particulates (health, acid rain).
Cracking & Alkenes
- Cracking splits large alkanes into smaller alkanes and alkenes.
- Alkenes: unsaturated hydrocarbons with a C=C double bond (e.g. ethene, propene).
- Bromine water test: alkenes decolorize bromine (turns colorless).
Triple Science: Polymers & Alcohols/Carboxylic Acids
- Alkenes form addition polymers; condensation polymers form when molecules join with loss of water.
- Alcohols: functional group -OH, general formula CnH2n+1OH; made by fermentation or hydration.
- Carboxylic acids: functional group -COOH; react with carbonates to form CO₂.
- Esters: formed from alcohol + carboxylic acid; sweet-smelling.
Chemical Analysis & Required Practicals
- Pure substances have fixed boiling/melting points; impure substances show ranges.
- Formulation: carefully measured mixture to achieve desired properties (paints, alloys, medicines).
- Paper chromatography separates mixtures based on solubility; RF = distance by substance/distance by solvent.
- Key gas tests: O₂ relights a glowing splint, H₂ ‘squeaky pop’, CO₂ turns limewater cloudy, Cl₂ bleaches damp litmus.
Triple Science: Instrumental & Ion Analysis
- Flame tests and flame emission spectroscopy identify metal ions by color/spectrum.
- Sodium hydroxide tests: color of precipitate indicates metal ion (e.g. Cu²⁺—blue, Fe²⁺—green, Fe³⁺—brown).
- Sulfate test: white precipitate with BaCl₂.
- Halide test: AgNO₃ gives white (Cl⁻), cream (Br⁻), yellow (I⁻) precipitate.
Atmosphere & Greenhouse Gases
- Modern atmosphere: ~80% N₂, ~20% O₂, small CO₂, H₂O vapor, noble gases.
- Early atmosphere: lots of CO₂, little/no O₂.
- Greenhouse gases (CO₂, H₂O vapor, CH₄) trap heat; human activity (burning fossil fuels, farming, deforestation) increases levels, contributing to climate change.
- Carbon footprint = total greenhouse emissions over a product’s life.
Sustainable Use of Resources & Metals
- Sustainable development meets current needs without harming future generations.
- Finite resources will run out; renewable resources replenish faster.
- Water treatment: filtration, sterilization (fresh water); desalination (sea water); waste water treatment uses screening, sedimentation, aerobic/anaerobic bacteria.
- Metal extraction: high-grade ores (traditional methods), low-grade (bioleaching, phytomining).
- Life cycle assessment considers environmental impact at all stages: materials, manufacturing, use, disposal.
Triple Science: Corrosion, Alloys, Polymers, Ceramics, Composites
- Corrosion: reaction with environment (rusting for iron—needs air + water).
- Prevent corrosion: barrier methods, galvanizing (sacrificial protection).
- Named alloys: bronze (copper/tin), brass (copper/zinc), steel types, gold alloys, aluminum alloys.
- Ceramics: clay (opaque), glass (transparent); both hard, brittle.
- Polymers’ properties depend on monomer and formation conditions.
- Thermosoftening polymers melt on heating; thermosetting do not (have cross-links).
- Composites combine materials for improved properties (e.g. reinforced concrete).
Haber Process & Fertilizers
- Haber process: N₂ + 3H₂ ⇌ 2NH₃; 450°C, 200 atm, Fe catalyst.
- High pressure increases yield but is dangerous/costly; temperature is a compromise (higher rate vs yield).
- Ammonia used for NPK fertilizers (contain nitrogen, phosphorus, potassium).
Key Terms & Definitions
- Activation Energy — Minimum energy for a reaction to occur.
- Homologous Series — Family of compounds with similar properties.
- Fraction — Group of hydrocarbons with similar boiling points.
- Saturated — Contains only single bonds.
- Unsaturated — Contains at least one double bond.
- Functional Group — Specific group of atoms causing chemical properties.
- Formulation — Mixture designed for a purpose.
- RF Value — Ratio of distances in chromatography.
- Pure (chemistry) — Substance with no impurities.
- Finite Resource — Will run out.
- Renewable Resource — Can be replenished.
- Corrosion — Destruction by chemical reaction with environment.
- Equilibrium — Forward and reverse reactions at equal rates.
Action Items / Next Steps
- Review required practical methods and identify variables.
- Practice calculations (rates, balancing, RF values, percentages).
- Memorize key definitions and tests (gas, ion, flame colors).
- Practice plotting and analyzing graphs.
- Revise named examples (alloys, polymers, processes) as specified.
- Work through exam questions and recall tasks as recommended.