Using Resources

• Heating homes, constructing shelter, producing food and moving people all draw on materials or energy taken from nature.
• Finite resources are used faster than they form; renewable resources can be replenished.
• Farmed timber and food crops supplement natural supplies; synthetic fibres and polymers can replace wool, cotton or timber in some uses.
• Chemistry improves agricultural and industrial processes so useful products can be made with fewer scarce inputs.

The punchline: Use data and orders of magnitude to judge significance, not labels alone.

• UK fresh water is usually filtered then sterilised.
• Chlorine, ozone or ultraviolet light can sterilise water.
• Fresh ground or surface water is generally easiest to treat; waste water needs several stages, while salty water needs energy-intensive desalination.
• Distillation or reverse osmosis desalinate salty water but need much energy.

The punchline: Potable is not the same as chemically pure; treatment effort depends on the source.

• Treat domestic and farm effluent for biodegradable material and pathogens; factory effluent may instead, or also, need hazardous chemicals removed.
• Screening and grit removal precede sedimentation.
• Sludge undergoes anaerobic digestion.
• Effluent receives aerobic biological treatment.

The punchline: Name the physical stages before the biological stages.

• In phytomining, plants take up metal compounds; burning the crop leaves an ash that can be processed.
• Bacteria release metal compounds from low-grade ore into a leach solution.
• Recover copper from that solution either with more-reactive scrap iron or by electrolysis.

The punchline: Compare lower landscape disruption with slow rates and further processing.

• Follow the product from resource extraction through making and packaging it, its working life, transport between stages and its eventual disposal.
• Changing which stages or impacts are counted can make a preferred product look greener, so advertising comparisons may be biased.
• Compare products across equivalent lifetimes and functions.
• Plastic bags use finite crude-oil feedstock and can persist as litter; paper bags use timber and can require substantial water and energy. Reuse and disposal can change the verdict.

The punchline: Check scope, data and value judgements before accepting a winner.

• Reduction, reuse and recycling can save limited raw materials and energy and reduce waste.
• A glass bottle may be reused; crushing and remelting glass is recycling.
• After sorting, metals can be melted and reshaped; feeding scrap steel back into production means less new iron must come from ore.

The punchline: Keep reuse distinct from recycling and compare the energy required.

• Compare nails in air plus water, boiled water under oil with little oxygen, and dry air over a desiccant; only the nail with both air and water rusts.
• Paint, grease and electroplating form barriers.
• Air gives aluminium a thin, adherent oxide barrier that blocks continued attack.
• Zinc galvanising also gives sacrificial protection because zinc is more reactive than iron.

The punchline: A controlled tube comparison shows both reactants are necessary; protection removes one or sacrifices another metal.

• Combine copper with tin for bronze, used in medals, statues and bearings; combine copper with zinc for brass, used in taps and musical instruments.
• 18-carat gold is 75% gold; alloyed gold is harder than pure gold and is used for durable jewellery.
• Cutting tools exploit the hardness and strength of brittle high-carbon steel; readily formed low-carbon grades suit car bodies.
• Chromium-nickel stainless steel resists corrosion in cutlery and sinks; low-density aluminium alloys suit aircraft.

The punchline: Link a named alloy's composition and property to the named use.

• Two recipes, two behaviours: heat sand with sodium carbonate and limestone for soda-lime glass; combine sand with boron trioxide for borosilicate, which melts only at a higher temperature.
• Firing fixes wet clay after shaping. Ethene can instead yield either LDPE or HDPE because changing the manufacturing conditions changes the resulting poly(ethene)'s properties.
• Uncross-linked thermosoftening chains can slide and soften on heating; a cross-linked thermosetting network instead retains its shape rather than flowing.
• A composite surrounds strengthening fibres or fragments with a continuous matrix; fibreglass, carbon-fibre composite and reinforced concrete are examples.

The punchline: Use structure and supplied numerical property data when choosing between materials.

• Nitrogen comes from air; hydrogen is obtained from natural gas. The purified gases enter in a 1:3 ratio.
• Nitrogen and hydrogen react reversibly: N₂ + 3H₂ ⇌ 2NH₃.
• An iron surface catalyses the gases at roughly 450 °C and 200 atmospheres.
• Cool to remove liquid ammonia and recycle unreacted gases.

The punchline: State the gas sources, 1:3 ratio, reversible equation, operating conditions, ammonia removal and gas recycling.

• On a temperature graph, rising temperature increases rate but decreases equilibrium ammonia yield because the forward reaction is exothermic.
• On a pressure graph, rising pressure increases rate and favours ammonia because the product side has fewer gas molecules.
• A catalyst raises rate at every condition but does not change the equilibrium-yield curve.
• Commercial conditions balance rate and yield with plant expense, reliable access to feedstocks and power, and what those inputs cost.

The punchline: Read each axis and trend first, then use collision theory or equilibrium to explain it.

• Industry mines phosphate rock plus potassium chloride and potassium sulfate. The rock needs chemical treatment; ammonia supplies nitrogen for nitric acid and ammonium salts.
• Treating phosphate rock with nitric acid produces phosphoric acid and calcium nitrate; sulfuric acid produces single superphosphate; phosphoric acid produces triple superphosphate.
• A school lab makes a salt in a small batch by neutralisation, then evaporation and crystallisation.
• Industry uses large-scale integrated processes, controlled feed rates and recycled streams to make consistent fertiliser formulations continuously.

The punchline: Compare raw materials, scale, control, separation and continuity—not simply the final salt name.