AQA GCSE Chemistry 8462: Using resources – Revision Notes

These revision notes cover Topic 10, Using resources (sections 4.10.1 to 4.10.4), of the AQA GCSE Chemistry (8462) specification, for teaching from September 2016 with GCSE exams from June 2018 (version 1.1). The topic is examined on Paper 2 at Foundation and Higher tier. Section 4.10.1.4 and the equilibrium part of 4.10.4.1 are Higher tier only and are marked below.

For full explanations and worked examples, read the Using resources study guide first. Then test yourself with the Using resources practice questions. The course hub is AQA GCSE Chemistry and the printable checklist lets you tick off each statement. The previous topic is Chemistry of the atmosphere.

Key definitions

Term	Meaning
Sustainable development	Meets the needs of current generations without compromising the ability of future generations to meet their own needs
Finite resource	Will run out; not replaced fast enough (crude oil, metal ores)
Renewable resource	Can be replaced as fast as it is used (timber, crops)
Potable water	Water that is safe to drink: low levels of dissolved salts and microbes
Pure water	Contains only water molecules – no dissolved substances
Desalination	Removing salts from salty water or sea water
Life cycle assessment (LCA)	Assessment of a product’s environmental impact at every stage of its life
Corrosion	Destruction of materials by chemical reactions with substances in the environment
Alloy	A mixture of a metal with other elements, usually other metals
Composite	A matrix (binder) surrounding a reinforcement of fibres or fragments
NPK fertiliser	A formulation of salts containing nitrogen, phosphorus and potassium

4.10.1 Water and extraction

Resource data and orders of magnitude (4.10.1.1). Read values carefully from charts, graphs and tables, with units. Comparing powers of ten shows significance: a reserve of about 10⁹ tonnes used at about 10⁷ tonnes per year lasts about 10⁹ ÷ 10⁷ = 10² = 100 years. One order of magnitude is a factor of 10.

Potable water in the UK – method in steps

1. Choose a suitable source of fresh water (ground water, lakes, rivers).
2. Pass through filter beds – removes solids.
3. Sterilise with chlorine, ozone or UV – kills microbes.

Salty water: desalination by distillation or reverse osmosis. Both need large amounts of energy.

Required practical 8 – method in steps

1. Test pH with universal indicator or a pH meter.
2. Weigh an evaporating basin. Evaporate a measured volume of the sample. Reweigh. Mass of dissolved solids = difference.
3. Divide by the volume in dm³ to get g/dm³.
4. Distil a sample: heat, condense the vapour, collect distillate.
5. Check the distillate: pH 7, boils at 100 °C, leaves no residue.

Sewage treatment in order: screening and grit removal → sedimentation (sludge + effluent) → anaerobic digestion of sludge → aerobic biological treatment of effluent.

Ease of making potable water: ground water (easiest) → waste water (more stages) → salt water (most energy).

Higher tier only – metal extraction from low-grade ores

Method	How it works
Phytomining	Plants absorb metal compounds → harvested → burned → ash contains metal compounds
Bioleaching	Bacteria produce leachate solutions containing metal compounds
Final step	Displacement with scrap iron, or electrolysis

Advantages: less digging, moving and disposal of rock; uses low-grade ores. Disadvantages: slow; phytomining needs land.

4.10.2 LCAs and recycling

LCA stages: raw materials → manufacture and packaging → use → disposal, plus transport at every stage.

• Easy to quantify: energy, water, resources, some wastes.
• Hard to quantify: pollutant effects (need value judgements).
• Shortened or selective LCAs can be misused, e.g. in advertising.

Plastic vs paper bags (typical points)

Stage	Plastic (poly(ethene))	Paper
Raw materials	Crude oil (finite)	Trees (renewable)
Manufacture	Less energy and water	More energy and water
Use	Can be reused several times	Usually used once; weak when wet
Disposal	Not biodegradable; can be recycled	Biodegradable; can be recycled

Reduce, reuse, recycle

• Reuse glass bottles (wash and refill).
• Recycle glass by crushing and melting.
• Recycle metals by melting and recasting.
• Scrap steel added to blast-furnace iron cuts ore extraction.
• The amount of separation needed depends on the material and the product required.

4.10.3 Materials

Rusting needs air and water. Nails in boiled water under oil (no air) or in dry air with a drying agent (no water) do not rust.

Prevention	How it works
Paint, grease, electroplating	Barrier keeps out air and water
Aluminium oxide layer	Natural barrier on aluminium
Galvanising (zinc)	Barrier, plus sacrificial protection: zinc is more reactive, so it corrodes instead of iron

Alloys

Alloy	Key point	Use
Bronze	Copper + tin	Statues
Brass	Copper + zinc	Door handles
Gold	Alloyed with silver, copper, zinc; 24 carat = 100%, 18 carat = 75%	Jewellery
High carbon steel	Strong, brittle	Cutting tools
Low carbon steel	Softer, easily shaped	Car bodies
Stainless steel	Chromium + nickel; hard, resists corrosion	Cutlery
Aluminium alloys	Low density	Aircraft

Formula: % gold = carat ÷ 24 × 100

Glass and ceramics

• Soda-lime glass: sand + sodium carbonate + limestone, heated.
• Borosilicate glass: sand + boron trioxide; higher melting point.
• Clay ceramics: wet clay shaped, then heated in a furnace.

Polymers

• LDPE and HDPE: both from ethene; different conditions (LD: very high pressure, trace of oxygen; HD: lower temperature and pressure, catalyst).
• Thermosoftening: no cross-links, weak forces between chains → melt on heating.
• Thermosetting: cross-links between chains → do not melt.

Composites: matrix + reinforcement, e.g. reinforced concrete, fibreglass, carbon fibre, wood.

4.10.4 Haber process and NPK

Haber process summary

Item	Detail
Product	Ammonia, NH₃
Equation	N₂ + 3H₂ ⇌ 2NH₃
Nitrogen source	Air
Hydrogen source	Natural gas
Catalyst	Iron
Temperature	About 450 °C
Pressure	About 200 atmospheres
Separation	Cool: ammonia liquefies and is removed
Unreacted gases	Recycled

Higher tier only – trade-offs

• Forward reaction exothermic: low temperature → higher yield but slower rate. 450 °C = compromise.
• 4 gas molecules → 2: high pressure → higher yield and faster rate, but costly equipment and energy. 200 atm = compromise.
• Catalyst: faster rate, same yield.

NPK – salts from phosphate rock

Treated with	Products
Nitric acid	Phosphoric acid and calcium nitrate
Sulfuric acid	Single superphosphate (calcium phosphate + calcium sulfate)
Phosphoric acid	Triple superphosphate (calcium phosphate)

Potassium chloride and potassium sulfate are mined. Ammonia makes ammonium salts and nitric acid.

Percentage by mass – worked reminder. Ammonia, NH₃: Mr = 14 + 3(1) = 17. % N = 14 ÷ 17 × 100 = 82.4%. Method: find Mr, multiply the element’s Aᵣ by the number of its atoms in the formula, divide by Mr, multiply by 100. Count atoms carefully inside brackets.

Lab vs industry: lab = small batch, titration and crystallisation, dilute reagents. Industry = continuous, large scale, integrated processes, raw materials made on site.

Must-know distinctions

• Potable vs pure water. Potable has safe, low levels of dissolved substances; pure has none.
• Reuse vs recycle. Reuse keeps the product as it is; recycling breaks it down into material for new products.
• Barrier vs sacrificial protection. A barrier fails when scratched; a more reactive metal still protects.
• Thermosoftening vs thermosetting. No cross-links (melt) vs cross-links (do not melt).
• Yield vs rate. Temperature moves them in opposite directions in the Haber process; a catalyst changes rate only.

Quick self-test

1. Why is potable water not pure?
2. Name three sterilising agents for potable water.
3. 10.0 cm³ of sea water leaves 0.35 g of residue. Calculate the dissolved solids in g/dm³.
4. Which stage of sewage treatment uses anaerobic digestion?
5. (Higher tier only) What does bioleaching produce?
6. Why is an LCA not purely objective?
7. Calculate the percentage of gold in 22 carat gold, to 3 significant figures.
8. Why does a scratched galvanised bucket not rust?
9. Explain why a thermosetting polymer does not melt.
10. Give the sources of nitrogen and hydrogen for the Haber process.
11. Calculate the percentage by mass of potassium in potassium nitrate, KNO₃, to 3 significant figures. (Aᵣ: K = 39, N = 14, O = 16)
12. Name the product when phosphate rock is treated with phosphoric acid.

Answers

1. It contains dissolved substances (salts).
2. Chlorine, ozone, ultraviolet light.
3. 0.35 ÷ 0.0100 = 35 g/dm³.
4. Treatment of sewage sludge.
5. Leachate solutions containing metal compounds.
6. Giving values to pollutant effects needs value judgements.
7. 22 ÷ 24 × 100 = 91.7%.
8. Zinc is more reactive than iron, so zinc reacts instead (sacrificial protection).
9. Cross-links between chains hold them in place.
10. Nitrogen from the air; hydrogen from natural gas.
11. Mr = 39 + 14 + 48 = 101; 39 ÷ 101 × 100 = 38.6%.
12. Triple superphosphate (calcium phosphate).

Where marks are usually lost

• Describing potable water as “pure” or “clean with nothing in it”.
• Putting sewage treatment stages in the wrong order, or mixing up which part (sludge or effluent) is treated aerobically.
• Saying desalination is used in the UK for most drinking water.
• Stating “rust needs oxygen” without water.
• Explaining galvanising only as a barrier.
• Giving “plastic” as an example of a composite.
• Claiming a catalyst increases the yield of ammonia.
• Writing “high temperature gives a higher yield” for the Haber process.
• Forgetting that unreacted nitrogen and hydrogen are recycled.
• Mixing up single and triple superphosphate.

Official syllabus

AQA GCSE Chemistry (8462) specification, for teaching from September 2016, GCSE exams June 2018 onwards, version 1.1, published by AQA – section 4.10 Using resources.