OCR GCSE Chemistry A: Improving processes and products (J248) – Revision Notes

These notes condense sub-topic C6.1 Improving processes and products from OCR’s Chemistry A (Gateway Science) specification for GCSE (9–1), code J248, in its Version 4.0 issue of August 2026. They cover learning outcomes C6.1a to C6.1s, the mathematical learning outcomes CM6.1i to CM6.1iv and the linked practicals (PAG C1, PAG C2, PAG C6). Statements C6.1c to C6.1f are Higher Tier only; the rest are tested at both tiers. The content is examined in Paper 2 (Foundation) or Paper 4 (Higher).

For full explanations and worked examples, use the Improving processes and products study guide. To practise exam-style questions, go to the practice set. Every J248 topic is linked from the course hub; print the J248 statement checklist to track progress, and take a free 10-minute diagnostic to spot gaps.

Key words

Term	Meaning
Ore	Rock from which a metal compound can be extracted at a profit
Reduction	Loss of oxygen (or gain of electrons)
Electrolysis	Breaking down an ionic compound, molten or in solution, using electricity
Bioleaching	Bacteria produce a metal-ion solution (leachate) from low-grade ore
Phytoextraction	Plants absorb metal ions; the burned plants leave metal-rich ash
Compromise conditions	Conditions balancing yield, rate and cost
Life-cycle assessment	Totals resource use and environmental impact from raw materials to disposal
Alloy	A metal mixed with one or more other elements; usually harder than the pure metal
Corrosion	A metal reacting with substances in its surroundings, such as oxygen and water
Sacrificial protection	A more reactive metal corrodes in place of the metal it is attached to
Composite	Two or more materials combined, for example fibres in a matrix

C6.1a: carbon extraction

Reactivity series (part): K, Na, Ca, Mg, Al, (C), Zn, Fe, Sn, Pb, (H), Cu, Ag, Au.

• Below carbon → heat oxide with carbon. Carbon is the reducing agent and becomes CO or CO₂.
• Above carbon → electrolysis.
• Iron: blast furnace, coke → carbon monoxide → reduces iron(III) oxide.
• Non-ferrous examples: copper, zinc, tin and lead oxides are reduced the same way.
• PAG C1: copper(II) oxide with carbon powder in a crucible, heated strongly; pink-brown copper forms.

Method: percentage of metal in an oxide. (1) Find Mr. (2) Divide the total Ar of the metal atoms by Mr. (3) Multiply by 100. Then the maximum mass of metal = mass of oxide × fraction.

C6.1b: electrolysis extraction

• Why: metal is above carbon, so carbon cannot remove the oxygen.
• Cost: large amounts of electricity, plus energy to melt the ore. Smelters are often near cheap electricity.
• Aluminium: oxide dissolved in molten cryolite (lower operating temperature). Cathode: Al³⁺ + 3e⁻ → Al. Anode: 2O²⁻ → O₂ + 4e⁻; oxygen burns the carbon anodes to CO₂, so they are replaced.
• PAG C2, inert electrodes:
  • NaCl(aq): hydrogen at the cathode (pop test), chlorine at the anode (bleaches damp litmus).
  • CuSO₄(aq): copper at the cathode (pink coating), oxygen at the anode (relights a glowing splint).
• Graph skill: mass deposited against time is a straight line; the gradient is the rate in g/min.

C6.1c: biological methods (Higher Tier only)

	Bioleaching	Phytoextraction
Works on	low-grade ore, waste tips	low-grade ore, contaminated soil
Product	leachate of metal ions	ash containing metal compounds
Then	scrap iron displacement or electrolysis	dissolve ash, then displacement or electrolysis
Good	low energy, no big mine	low energy, cleans land, little visible damage
Bad	slow; toxic leachate risk	slow; needs land; burning releases CO₂

C6.1d–f: industrial conditions (Higher Tier only)

	Haber	Contact
Equation	N₂ + 3H₂ ⇌ 2NH₃	2SO₂ + O₂ ⇌ 2SO₃
Forward reaction	exothermic	exothermic
Temperature	about 450 °C	about 450 °C
Pressure	about 200 atm	close to atmospheric
Catalyst	iron	vanadium(V) oxide
Why that pressure	fewer gas molecules on the right, so high pressure helps yield and rate; higher still costs too much	yield already high, so extra pressure is not worth the cost

Method: explaining a compromise. (1) State which direction the change favours (Le Chatelier). (2) State its effect on rate. (3) State the cost or safety effect. (4) Conclude why the chosen value balances them.

Raw materials and energy (C6.1f): nitrogen from air, hydrogen from natural gas and steam, sulfur for SO₂. Cheap, plentiful raw materials and recycling of unreacted gas allow a lower yield per pass. Energy for heating and compression is a running cost.

C6.1e and CM6.1i–iv: rate graphs

• Rate = change in amount ÷ time (arithmetic and ratio, CM6.1i).
• Plot product against time; the curve flattens as reactants are used up (CM6.1ii).
• Instantaneous rate = gradient of a tangent: rise ÷ run, with units such as cm³/s (CM6.1iii).
• If doubling a condition doubles the rate, rate is directly proportional to it: a straight line through the origin (CM6.1iv).
• Higher temperature, pressure or concentration and a catalyst all give steeper initial gradients.

C6.1g: Haber process and farming

Ammonia → nitrogen fertilisers → more protein in crops → higher yields. Without synthetic ammonia, far fewer people could be fed.

C6.1h–j: fertilisers

• N, P, K are the elements crops most often run short of. Compounds must be soluble.
• Nitrogen: ammonium salts and nitrates. Phosphorus: from phosphate rock treated with acid. Potassium: from potassium chloride, which is mined.
• Integrated site: Haber plant → ammonia; part oxidised → nitric acid; ammonia + nitric acid → ammonium nitrate; Contact plant → sulfuric acid; ammonia + sulfuric acid → ammonium sulfate.
• PAG C6 laboratory route: titrate ammonia solution (or potassium hydroxide solution) with dilute sulfuric acid using an indicator; repeat without indicator; evaporate and crystallise.

	Laboratory	Industry
Scale	grams, batch	tonnes, continuous
Reactants	bought, dilute	made on site, concentrated
Energy	heating to evaporate	reaction heat reused

C6.1k–l: life-cycle assessment

Four stages, each with resource use and environmental impact:

1. Raw materials and manufacture.
2. Use.
3. Transport.
4. Disposal (landfill, incineration, recycling).

Method: interpreting LCA data. (1) Add each product’s total for one measure. (2) Scale to the same number of uses or years. (3) Compare. (4) Name a factor the data miss, such as pollution or how long the product lasts, and note that some judgements are subjective.

C6.1m–n: recycling

• Recycling into a different product: crushed glass as road aggregate or sand; plastic bottles into fibres for clothing or carpets; old tyres into play-area surfacing.
• Viable when: bulk supply is reliable, the new use tolerates impurities, it saves raw materials, energy or landfill.
• Decision factors: collection and sorting costs, energy and transport, ease of separating mixed materials, market price, scarcity of the raw material, landfill charges.

C6.1o–q: alloys and corrosion

Alloy	Composition	Use
Steel	iron + carbon (stainless: + chromium, nickel)	construction, cutlery
Brass	copper + zinc	fittings, instruments
Bronze	copper + tin	statues, bearings
Solder	tin + lead, or tin + small amounts of copper or silver	electrical joints (low melting point)
Duralumin	aluminium + about 4% copper, small amounts of magnesium and manganese	aircraft (strong, low density)

• Rusting needs oxygen and water; salt speeds it; rust is hydrated iron(III) oxide and flakes off.
• Aluminium’s oxide layer protects it, so it corrodes very little.
• Barrier: paint, oil, grease, plastic, electroplating. Fails once scratched.
• Sacrificial: zinc or magnesium, more reactive than iron, oxidises first. Galvanising does both.

C6.1r–s: materials

Material	Typical strengths	Typical weaknesses
Glass	transparent, hard, unreactive	brittle
Clay ceramic	hard, high melting point, insulator	brittle, heavy
Polymer	low density, flexible, insulator	low melting point, weaker
Composite	strong for its density	expensive, hard to recycle
Metal	strong, tough, conducts, can be shaped	dense, may corrode

Quantitative comparison: work out a ratio such as strength ÷ density or cost per kilogram, then pick the material that best matches the stated use.

Quick self-test

1. Name the element that sits between aluminium and zinc in the reactivity series.
2. State why magnesium cannot be extracted by heating its oxide with carbon.
3. Calculate the percentage of lead in lead(II) oxide, PbO (Pb = 207, O = 16).
4. Give the products at each electrode when aqueous copper sulfate is electrolysed with inert electrodes.
5. State why the carbon anodes in aluminium extraction must be replaced.
6. (Higher Tier only) Give one advantage and one disadvantage of phytoextraction.
7. (Higher Tier only) State the catalyst and temperature used in the Contact process.
8. (Higher Tier only) A tangent passes through (10 s, 0 cm³) and (50 s, 30 cm³). Calculate the rate.
9. Calculate the percentage of nitrogen in calcium nitrate, Ca(NO₃)₂ (Ca = 40, N = 14, O = 16).
10. A lab preparation should give 4.5 g of ammonium sulfate. It gives 3.6 g. Calculate the percentage yield.
11. Name the four stages of a life-cycle assessment.
12. Explain why a scratched galvanised bucket does not rust.

Answers

1. Carbon.
2. Magnesium lies above carbon in the reactivity series; carbon cannot take its oxygen.
3. Mr = 223; 207 ÷ 223 × 100 = 92.8%.
4. Cathode: copper. Anode: oxygen.
5. Oxygen made at the anode reacts with the hot carbon to form carbon dioxide, so the anodes wear away.
6. Advantage: low energy or uses low-grade ore. Disadvantage: very slow or needs large areas of land.
7. Vanadium(V) oxide; about 450 °C.
8. 30 ÷ 40 = 0.75 cm³/s.
9. Mr = 164; 28 ÷ 164 × 100 = 17.1%.
10. 3.6 ÷ 4.5 × 100 = 80.0%.
11. Raw materials and manufacture; use; transport; disposal.
12. Zinc is more reactive than iron, so it oxidises instead (sacrificial protection).

Where marks are usually lost

• Writing “carbon is more reactive than aluminium”. It is less reactive.
• Saying cryolite “dissolves the aluminium”. It dissolves the aluminium oxide.
• Mixing up electrodes in PAG C2: hydrogen and copper form at the cathode.
• (Higher Tier) Saying a catalyst shifts equilibrium or raises yield.
• (Higher Tier) Explaining 450 °C with yield only; rate and cost must be in the answer too.
• (Higher Tier) Reading the gradient of a curve from two points on the curve instead of from a tangent.
• Forgetting that fertilisers must be soluble.
• Comparing LCA totals without putting both products on the same number of uses.
• Stating that rust is iron oxide made by oxygen alone; water is needed too.
• Choosing a material without linking a named property to the stated use.

Official syllabus

Source document, published by OCR: the GCSE (9–1) Chemistry A (Gateway Science) specification, code J248, Version 4.0, August 2026, with first assessment in 2018. Used here: sub-topic C6.1 Improving processes and products, with statements C6.1a–C6.1s, maths outcomes CM6.1i–CM6.1iv and the PAG C1, PAG C2 and PAG C6 practical suggestions.