Chemistry of the Environment

Worked examples (12)extended set

• 1Boiling point and a cobalt(II) chloride test on lake water (multiple choice)
• 2Beneficial and harmful substances in river water
• 3The four stages of treating a domestic water supply
• 4Hydrated cobalt(II) chloride: formula and colour change (multiple choice)
• 5Heating hydrated copper(II) sulfate and testing the liquid
• 6Percentage of water in hydrated cobalt(II) chloride
• 7Finding x in hydrated magnesium sulfate by heating to constant mass
• 8Heating curves: which water sample is pure?
• 9Distilling sea water, and why labs use distilled water
• 10Dissolved oxygen: from mg/dm³ to moles and gas volume
• 11Testing well water for nitrate and checking the safe limit
• 12Chlorine dose for a day's water supply

Model answers (6)

• ✓Model answer — Paper 4 short-answer style
• ✓Model answer — Paper 4 short-answer style
• ✓Model answer — Paper 4 structured style
• ✓Model answer — Paper 4 (Extended) structured style
• ✓Model answer — Paper 4 (Extended) structured style
• ✓Model answer — Paper 4 (Extended) extended-response style

Worked examples (12)extended set

• 1Reading the composition of clean, dry air from a pie chart
• 2Matching air pollutants to their sources and effects
• 3Measuring the percentage of oxygen in air with heated copper
• 4Where do oxides of nitrogen in exhaust gas come from? (multiple choice)
• 5Catalytic converter: equation and redox
• 6Car exhaust statements: spotting the one that is not correct (multiple choice)
• 7Incomplete combustion of octane: carbon monoxide and particulates
• 8Flue gas desulfurisation: how much calcium oxide?
• 9Nitrogen monoxide and engine temperature: reading a graph
• 10Testing exhaust gas for sulfur dioxide and carbon dioxide
• 11City air-quality data: percentage decreases and the strategies behind them
• 12Limiting reactant in a catalytic converter: gas volumes

Model answers (6)

• ✓Model answer — Paper 4 short-answer style
• ✓Model answer — Paper 4 short-answer style
• ✓Model answer — Paper 4 structured style
• ✓Model answer — Paper 4 structured style
• ✓Model answer — Paper 4 (Extended) structured style
• ✓Model answer — Paper 4 (Extended) structured style

Worked examples (6)

• 1The roles of N, P and K
• 2Name and write formulae for nitrogenous fertilisers
• 3Make ammonium nitrate by neutralisation
• 4Link the Haber process to fertilisers
• 5Percentage of nitrogen in ammonium nitrate
• 6Explain the eutrophication oxygen-depletion chain

Model answers (6)

• ✓Model answer — Paper 4 short-answer style
• ✓Model answer — Paper 4 short-answer style
• ✓Model answer — Paper 4 structured style
• ✓Model answer — Paper 4 calculation style
• ✓Model answer — Paper 4 (Extended) structured style
• ✓Model answer — Paper 4 (Extended) structured style

Worked examples (12)extended set

• 1True statements about methane and carbon dioxide (multiple choice)
• 2Fossil fuels and the sources of carbon dioxide and methane
• 3How greenhouse gases cause global warming: reading an energy diagram
• 4Why more methane means more warming (multiple choice)
• 5Complete combustion of methane: masses and gas volumes
• 6Showing that a fuel produces water and carbon dioxide
• 7Photosynthesis: symbol equation and reacting masses
• 8Rising carbon dioxide levels: interpreting the graph
• 9Which fuel releases less carbon dioxide per 1000 kJ?
• 10Matching strategies to climate change and acid rain
• 11Bond energies for burning methane and the reaction pathway diagram
• 12Burning methane in a gas syringe: volumes before and after

Model answers (6)

• ✓Model answer — Paper 4 short-answer style
• ✓Model answer — Paper 4 short-answer style
• ✓Model answer — Paper 4 structured style
• ✓Model answer — Paper 4 (Extended) structured style
• ✓Model answer — Paper 4 (Extended) structured style
• ✓Model answer — Paper 4 (Extended) structured style

Worked examples (12)extended set

• 1Sulfur dioxide, acid rain and how to cut emissions
• 2Identifying an unknown sulfate from test results
• 3Contact process flow chart: sources, conditions and equation
• 4Reading an equilibrium graph to justify the Contact process temperature
• 5Contact process conditions (multiple choice)
• 6Roasting sulfide ores: balancing and gas volume
• 7Sulfur dioxide decolourising potassium manganate(VII): a redox reaction
• 8Making hydrated copper(II) sulfate: method and percentage yield
• 9Titration with sulfuric acid: burette readings to concentration
• 10Flue gas desulfurisation: how much calcium oxide?
• 11Reaching equilibrium: concentration–time graph and changing conditions
• 12Comparing the sulfur content of fuels (practical)

Model answers (6)

• ✓Model answer — Paper 4 short-answer style
• ✓Model answer — Paper 4 short-answer style
• ✓Model answer — Paper 4 structured style
• ✓Model answer — Paper 4 structured style
• ✓Model answer — Paper 4 (Extended) structured style
• ✓Model answer — Paper 4 (Extended) structured style

Worked examples (12)extended set

• 1Observations when copper(II) carbonate reacts with nitric acid
• 2Which mixture forms a carbonate precipitate? (multiple choice)
• 3Carbonates with acids: symbol and ionic equations
• 4Making magnesium nitrate crystals from magnesium carbonate
• 5Gas syringe calculation: potassium carbonate with acid
• 6Volume–time graph for marble chips and acid
• 7Limestone in the blast furnace: quicklime and slag
• 8Purity of limestone by heating to constant mass
• 9Identifying a carbonate from tests (multiple choice)
• 10Identifying an unknown carbonate from practical tests
• 11Percentage of sodium carbonate in a mixture by gas volume
• 12Identifying a metal from the thermal decomposition of its carbonate

Model answers (6)

• ✓Model answer — Paper 4 short-answer style
• ✓Model answer — Paper 4 / Paper 6 chemical-tests style
• ✓Model answer — Paper 4 structured style
• ✓Model answer — Paper 4 (Extended) structured style
• ✓Model answer — Paper 4 structured style
• ✓Model answer — Paper 4 (Extended) extended-response style