Eduqas GCSE Chemistry · Topic 11 — Production, use and disposal of important chemicals and materials
Mini-Lesson
Production, Use & Disposal of Important Chemicals & Materials
This mini-lesson walks you through the core of Eduqas Topic 11: making ammonia (Haber) and fertilisers, corrosion and its prevention, recycling, life cycle assessment, and choosing materials — plus two useful extras: making sulfuric acid (Contact) and potable water (Eduqas Topic 12).
Make a guess: why do ammonia plants run so hot?
Mission 1Why do ammonia plants run so hot?
Mission 2How does river water become safe to drink?
Mission 3Why let one metal corrode to save another?
Mission 4How do you judge a product's whole impact?
Work through each screen, answer the questions as you go (some are wordy, some are calculations, some are sorting games) and collect ⭐ stars. HT marks Higher-tier-only ideas. Press Start.
Making ammonia — the Haber process
Pulling nitrogen out of the air
Plants need nitrogen to grow, but they can't use the unreactive N₂ in the air. The Haber process combines nitrogen and hydrogen to make ammonia (NH₃), the starting point for fertilisers.
N₂ + 3H₂ ⇋ 2NH₃
nitrogen (from the air) + hydrogen (from natural gas) ⇋ ammonia · the ⇋ means it is reversible
The Haber process: gases pass over an iron catalyst at ~450 °C and ~200 atm; ammonia is cooled to a liquid and removed; unreacted gases are recycled.
Temperature ~450 °C — a compromise (more later).
Pressure ~200 atmospheres — high, but safe and affordable.
Iron catalyst — speeds the reaction up; it does not change how much ammonia forms.
Ammonia is cooled and liquefied to remove it; unreacted N₂ and H₂ are recycled.
⚠️ Misconception: the conditions are a compromise, not the "best" for yield. The Haber reaction is reversible — it never goes 100% to ammonia in one pass, which is exactly why the gases are recycled.
Higher tier · the compromise
Why those exact conditions?
The forward reaction (making ammonia) is exothermic and the gas particles decrease (4 molecules → 2). Le Chatelier's principle predicts the "ideal" yield conditions — but real factories compromise:
Change
Best for yield
Real compromise
Temperature
low (exothermic ⇒ more NH₃)
~450 °C — low temp is too slow
Pressure
high (fewer gas molecules on right)
~200 atm — higher is too costly/unsafe
In a sentence: low temperature gives a higher equilibrium yield but a slower rate; 450 °C trades a little yield for a much faster reaction, and recycling unreacted gas mops up the loss. High pressure helps yield but big pressures need expensive, strong equipment — so ~200 atm is the balance.
Check your understanding
Why about 450 °C?
?In the Haber process, why is a temperature of about 450 °C used rather than a much lower temperature?
Higher tier · reasoning
Raise the pressure
?N₂ + 3H₂ ⇋ 2NH₃. Using Le Chatelier's principle, what happens to the equilibrium yield of ammonia if the pressure is increased?
Mission 1 check
Why do ammonia plants run so hot?
?A company finds a new catalyst that makes the Haber reaction fast enough at 300 °C. Why might it run its plant at 300 °C instead of about 450 °C?
NPK fertilisers
From ammonia to feeding crops
Plants need three main elements from the soil. Fertilisers replace them so crops grow well:
P — Phosphorus (e.g. phosphate compounds) → roots.
K — Potassium (e.g. potassium chloride/sulfate) → flowers & fruit.
An NPK fertiliser is a formulation — a carefully mixed product containing all three. Ammonia from the Haber process is reacted with acids (e.g. nitric acid → ammonium nitrate; sulfuric acid → ammonium sulfate) to make the nitrogen salts.
💡 Link: the Haber process exists mainly to feed the world — most ammonia becomes fertiliser. Over-use, though, causes problems like eutrophication when fertiliser washes into rivers.
Extra · the Contact process (not on the Eduqas spec)
One of the world's most-used chemicals
Sulfuric acid (H₂SO₄) is made industrially by the Contact process, in three stages:
S + O₂ → SO₂ 2SO₂ + O₂ ⇋ 2SO₃ SO₃ + H₂O → H₂SO₄
burn sulfur → make sulfur dioxide; oxidise it to sulfur trioxide over a vanadium(V) oxide catalyst at ~450 °C; absorb SO₃ to form sulfuric acid
The key reversible step is 2SO₂ + O₂ ⇋ 2SO₃.
Catalyst: vanadium(V) oxide (V₂O₅).
Conditions: about 450 °C and roughly 1–2 atmospheres — a compromise of yield, rate and cost.
⚠️ Don't mix them up: the Haber process makes ammonia (iron catalyst); the Contact process makes sulfuric acid (vanadium(V) oxide catalyst). Both use a reversible step and a compromise temperature near 450 °C.
Check your understanding
Name the catalyst
?Which catalyst is used in the Contact process to make sulfuric acid?
Mission 2 of 4
How does river water become safe to drink?
Make a guess: how does river water become safe to drink?
Potable water (Eduqas Topic 12)
Making water safe to drink
Potable water is water that is safe to drink — low in dissolved salts and microbes. It is not the same as pure water, which is only H₂O molecules.
Treating fresh water: filter out solids, then sterilise (chlorine, ozone or UV) to kill microbes.
Filtration through beds of sand/gravel removes insoluble solids.
Sterilisation kills microbes — by chlorination, ozone, or ultraviolet (UV) light.
Where fresh water is scarce, sea water is treated by desalination — using distillation or membranes (reverse osmosis). Distillation needs lots of energy.
⚠️ Misconception:potable ≠ pure. Potable water still contains dissolved salts; it just has safe, low levels of them and no harmful microbes. Pure water would taste flat and is expensive to make.
Mission 2 check
How does river water become safe to drink?
?A town takes its water from a river. The water carries mud and harmful microbes. Which treatment makes it safe to drink?
Practical skills
Analysing & purifying a water sample
In a common class practical you analyse water samples from different sources, then purify one by distillation:
Measure the pH of each sample and compare with pure water (pH 7).
Evaporate a sample to dryness to reveal any dissolved solids — a clean watch glass left after evaporation shows almost none.
Distil a sample: heat to boiling, condense the steam, and collect pure water in the receiver. Distilled water boils at 100 °C and leaves the dissolved solids behind.
🔎 Why distillation works: only the water turns to vapour and condenses; the dissolved salts (which have much higher boiling points) stay in the flask, so the collected liquid is pure. Note: this is not one of the Eduqas specified practicals — the one listed for Topic 11 is SP11, finding the percentage of water in a hydrated salt such as copper(II) sulfate (next screen).
Specified practical SP11
How much water is in a hydrated salt?
Blue hydrated copper(II) sulfate crystals contain water of crystallisation. Heating drives it off, leaving white anhydrous copper(II) sulfate:
CuSO₄·5H₂O → CuSO₄ + 5H₂Oblue hydrated → white anhydrous + water (driven off as steam)
Weigh an empty crucible, then the crucible + hydrated salt.
Heat, let it cool, reweigh. Repeat until the mass stops changing (heat to constant mass), so all the water has gone.
Mass of water = mass before heating − mass after heating.
% water = (mass of water ÷ mass of hydrated salt) × 100
Worked example: 2.50 g of hydrated salt leaves 1.60 g after heating. Water = 0.90 g, so % water = (0.90 ÷ 2.50) × 100 = 36%. That matches the formula: 5H₂O = 90 out of Mr 249.5 ≈ 36%.
Check your understanding
Potable or pure?
?A student says "potable water is the same as pure water." Why is this wrong?
Game · put the steps in order
Treat the water
Tap the water-treatment steps in the correct order, from raw source to safe drinking water.
Tap them one at a time, earliest first.
Order so far
Mission 3 of 4
Why let one metal corrode to save another?
Make a guess: why bolt a zinc block onto a steel ship?
Corrosion & rusting
Why iron rusts
Corrosion is the breaking down of a metal by reaction with its environment. For iron and steel, corrosion is called rusting, and it needs both:
iron + oxygen + water → hydrated iron(III) oxide (rust)
The classic experiment: iron only rusts when both air (oxygen) and water are present. Boiled water has the dissolved air driven out and the oil keeps it out; the drying agent (anhydrous calcium chloride) keeps the air dry.
⚠️ Misconception: rusting needs BOTH oxygen and water — remove either one and it stops. Salt water speeds it up but isn't required.
Preventing corrosion
Two big ideas: barriers & sacrifice
Barrier methods — keep out air and water with paint, oil/grease, plastic coating or electroplating. If the barrier is scratched, rusting starts there.
Galvanising — coating iron with zinc. The zinc is a barrier and works sacrificially.
Sacrificial protection — attach a more reactive metal (e.g. zinc or magnesium). It corrodes instead of the iron, because it loses electrons more readily.
Sacrificial protection: a more reactive metal (magnesium or zinc) corrodes instead of the iron.
⚠️ Misconception: the sacrificial metal must be MORE reactive than iron, not less. A less reactive metal would let the iron corrode first.
Check your understanding
Why bolt on magnesium?
?An iron gate is protected by bolting blocks of magnesium to it. Why does this stop the iron rusting?
Mission 3 check
Why let one metal corrode to save another?
?A galvanised (zinc-coated) steel bucket gets a deep scratch, so bare steel shows. Months later, the steel at the scratch has still not rusted. Why?
Mission 4 of 4
How do you judge a product's whole impact?
Make a guess: how do you judge a product's whole impact?
Recycling materials
Why recycle?
Most metals come from finite ores and extracting them takes a lot of energy and causes pollution. Recycling metals and other materials:
Conserves the limited supply of ores (and other raw materials).
Saves energy — recycling a metal usually uses much less energy than extracting it from ore.
Reduces waste sent to landfill and cuts mining/quarrying damage and CO₂.
Steel is separated with magnets; aluminium, glass and many plastics are sorted, melted and re-formed. Recycling is rarely perfect — sorting and contamination add cost.
💡 Tip: "reduce, reuse, recycle" — reusing an object (a glass bottle refilled) saves even more than melting it down to recycle.
Life cycle assessment (LCA)
Cradle to grave
A life cycle assessment works out the total environmental impact of a product across its whole life, in four stages:
The four stages of a life cycle assessment, from raw materials to disposal; the dashed arrow shows recycling feeding material back to the start.
1. Raw materials — extracting and processing them (energy, mining damage).
2. Manufacturing — making the product (energy, waste, transport).
3. Use — impacts while it is used (energy, emissions).
4. Disposal — landfill, incineration or recycling at end of life.
⚠️ Misconception: an LCA covers the whole life, not just manufacture. A product that is "green" to make can still be worse overall if it's energy-hungry to use or hard to dispose of. (Judging impacts also involves opinion, so LCAs can be biased.)
Check your understanding
Which LCA stage?
?Which of these belongs to the disposal stage of a life cycle assessment?
Mission 4 check
How do you judge a product's whole impact?
?An advert says a new electric toothbrush is eco-friendly because it uses very little electricity. How should its whole environmental impact be judged?
Choosing materials
Alloys, polymers, ceramics & composites
Different jobs need different properties, so we choose (or design) materials to match:
Alloys — mixtures of a metal with other elements (e.g. steel, brass, bronze). Usually harder and stronger than the pure metal.
Polymers — long-chain molecules. Two types (below).
Ceramics — e.g. clay pottery and glass. Hard, brittle, heat-resistant, electrical insulators.
Composites — two materials combined (e.g. fibreglass, carbon fibre, reinforced concrete): a strong reinforcement held in a matrix, giving the best of both.
Two kinds of polymer
Thermosoftening — separate tangled chains. They soften when heated and can be remelted and reshaped again and again (so they recycle easily).
Thermosetting — chains held by strong cross-links. They are rigid and do not melt when heated (they char/burn instead).
⚠️ Misconception:thermosetting plastics can't be re-melted. The cross-links lock the structure, so once set they keep their shape even when hot — unlike thermosoftening plastics.
Game · match the material to its property
Pick the right material
Tap a material on the left, then its best-matching property/use on the right.
Material
Property / use
Check your understanding
Thermosoftening or thermosetting?
?Which statement about a thermosoftening polymer is correct?
Recap
Topic 11 in a nutshell
Haber: N₂ + 3H₂ ⇌ 2NH₃ · iron · ~450 °C · ~200 atm · a compromise; gases recycled.
NPK: N, P, K fertilisers feed crops; ammonia + acids → nitrogen salts.