Using resources — section overview

Section C10 covers sustainability, materials science and water treatment — how chemistry helps us use Earth's resources more responsibly.

Natural resources and sustainability

Finite (non-renewable) resources: fossil fuels, metal ores, minerals — will run out eventually. Renewable resources: wood, crops, solar energy, wind.

Sustainable development: meeting the needs of the present without compromising the ability of future generations to meet their needs.

Life Cycle Assessment (LCA): evaluates environmental impact of a product through its whole life:

1. Extraction and processing of raw materials
2. Manufacturing and packaging
3. Use during lifetime
4. Disposal at end of life

LCA helps compare products and identify where environmental impact can be reduced.

Metal extraction and recycling

Most metals are extracted from ores by:

• Reduction with carbon (iron, copper, lead)
• Electrolysis (aluminium, sodium)
• Phytoremediation / bioleaching (copper from low-grade ores)

Bioleaching: bacteria oxidise metal sulfide ores → metal ions in solution → electrolysis extracts metal.

Recycling advantages: uses less energy than primary extraction; reduces landfill; conserves finite resources.

The Haber process

Industrial production of ammonia: N₂ + 3H₂ ⇌ 2NH₃ (ΔH = −92 kJ/mol)

Conditions: temperature ~450°C (compromise between rate and yield), pressure ~200 atm, iron catalyst.

Ammonia is used to make fertilisers (ammonium nitrate, ammonium sulfate) and nitric acid.

Making fertilisers

NPK fertilisers contain nitrogen (N), phosphorus (P) and potassium (K).

• N: from ammonia → ammonium salts or nitrates
• P: from phosphate rock + acid → soluble phosphate
• K: from potassium chloride deposits

Fertilisers increase crop yields; BUT over-use can cause eutrophication (excess nitrates/phosphates run into water → algal bloom → water deoxygenated → organisms die).

Water treatment

Potable (drinking) water must be safe to drink — low levels of dissolved substances, microorganisms removed.

Steps to produce potable water:

1. Sedimentation — particles settle
2. Filtration — sand/gravel filters remove remaining particles
3. Chlorination — kills bacteria and other microorganisms

Desalination: removing salt from sea water — distillation or reverse osmosis. Expensive and energy-intensive.

Waste water treatment: screening → settling tank (sedimentation) → biological treatment (bacteria break down organic matter) → UV treatment → release.

Common exam mistakes in C10

1. Recycling is always better — not always true for LCA; some recycling processes use more energy than primary production (e.g. glass)
2. Chlorination makes water taste bad — sometimes, but it is essential for safety; small amounts are harmless
3. Eutrophication — oxygen decreases, not increases — algae block light → plants die → bacteria decompose them using O₂ → water deoxygenated