Corrosion, alloys, ceramics, polymers & composites (Chem only) – GCSE Chemistry exam questions with mark scheme

1Grade 1–3FoundationTriple only5 marks

(a) What is meant by corrosion?

Tick (✓) one box. [1]

☐ A metal wearing away because it is rubbed against another surface.
☐ A material being destroyed by chemical reactions with substances in its environment.
☐ A metal turning into a liquid when it is heated strongly.
☐ A material dissolving in water without any chemical reaction.

(b) Draw one line from each alloy to the metals it mainly contains. [3]

Alloy		Metals mainly in the alloy
brass		aluminium and magnesium
bronze		copper and tin
stainless steel		copper and zinc
		iron, chromium and nickel

(a) a material being destroyed by chemical reactions with substances in its environment (more than one box ticked = 0)(1)
(b) brass → copper and zinc(1)
(b) bronze → copper and tin(1)
(b) stainless steel → iron, chromium and nickel (more than one line from an alloy cancels the mark for that alloy)(1)
(c) water and oxygen both needed; allow air for oxygen; allow moisture / water vapour for water; ignore salt(1)
Answer: (a) destroyed by chemical reactions with substances in the environment; (b) brass – copper and zinc, bronze – copper and tin, stainless steel – iron, chromium and nickel; (c) water and oxygen (air)
Examiner tip: Brass and bronze are the classic mix-up: brass has zinc, bronze has tin – and (c) needs both water and oxygen for the one mark.

2Grade 4–5Triple only5 marks

A student set up the three test tubes shown in the diagram to find out what is needed for iron to rust.

The tubes were left for one week. The table shows the results.

Tube	Did the nail rust?
A	yes
B	no
C	no

(a) Why was the water in tube B boiled before the nail was added? [1]

(b) Give the reason for the layer of oil in tube B. [1]

(d) What do the results for tubes A, B and C show about the conditions needed for iron to rust? [2]

(a) to remove dissolved air / oxygen (from the water) allow to remove gases; ignore to kill bacteria / to sterilise(1)
(b) to stop air / oxygen (re)dissolving in the water allow to keep air / oxygen out (of the water)(1)
(c) to absorb water (vapour) from the air in the tube or so the air / tube is dry (so there is no water) allow removes moisture(1)
(d) iron needs both water and oxygen / air to rust allow rusting needs water and air together(1)
(d) tube B shows water without oxygen does not cause rusting and tube C shows oxygen / air without water does not cause rusting both comparisons needed for this mark(1)
Answer: (a) to remove dissolved oxygen/air; (b) to stop air dissolving back into the water; (c) to remove water vapour so the air is dry; (d) rusting needs both water and oxygen – B (no oxygen) and C (no water) did not rust
Examiner tip: In (d) say what each control tube removes: B has water but no air, C has air but no water – only A has both.

3Grade 4–5Triple only5 marks

The purity of gold is measured in carats. Pure gold is 24 carat.

(a) Gold used for jewellery is usually an alloy of gold with silver, copper and zinc.

Give one reason, in terms of its properties, why pure gold is not usually used for jewellery. [1]

(b) A necklace is made of 9 carat gold. The necklace has a mass of 12.8 g.

Calculate the mass of gold in the necklace. [2]

Calculate the carat value of the gold in the ring. [2]

(a) pure gold is too soft or the alloy is harder (so it does not bend / scratch / wear away as easily) allow pure gold bends easily; ignore cheaper / stronger on its own; ignore shinier(1)
(b) $\dfrac{9}{24} \times 12.8$ allow 0.375 × 12.8 or 37.5% of 12.8(1)
(b) 4.8 (g) correct answer scores 2 marks(1)
(c) $\dfrac{5.25}{7.0}$ (= 0.75) allow 75%(1)
(c) (0.75 × 24 =) 18 (carat) correct answer scores 2 marks(1)
Answer: (a) pure gold is too soft; (b) 4.8 g; (c) 18 carat
Examiner tip: A carat value is parts out of 24, not out of 100: 9 carat means 9/24 of the mass is gold, and to find a carat value multiply the fraction of gold by 24.

4Grade 1–3FoundationTriple only5 marks

Steel is an alloy of iron. The table gives information about three types of steel.

Type of steel	Properties
high carbon steel	very strong but brittle
low carbon steel	softer and easily shaped
stainless steel	hard and resistant to corrosion

(a) Stainless steel contains iron and carbon. Name two other elements added to make stainless steel. [1]

(b) A car maker presses sheets of steel into curved shapes to make car body panels.

Which type of steel should the car maker use? Give a reason for your answer. [2]

(d) Knives and forks are washed in water many times.

Give one reason why stainless steel is used to make knives and forks. [1]

(a) chromium and nickel both needed; allow Cr and Ni(1)
(b) low carbon steel(1)
(b) (because it is) easily shaped / softer allow malleable / can be bent (into shape) easily; reason only scores if low carbon steel chosen(1)
(c) it is brittle so it would crack / break (when pressed into shape or in a crash) allow it is hard to shape; ignore it is too strong(1)
(d) it does not corrode / rust allow resists corrosion; allow it is hard so it does not bend / wear / go blunt; ignore hard on its own with no consequence(1)
Answer: (a) chromium and nickel; (b) low carbon steel – easily shaped; (c) brittle, so it would crack; (d) it resists corrosion / does not rust (or: it is hard so it does not bend or wear)
Examiner tip: Match the property in the table to what the product has to do – pressed into shape needs ‘easily shaped’, washed in water needs ‘resists corrosion’.

5Grade 4–5Triple only5 marks

Aluminium alloys are used to build aircraft. The table gives information about some metals and alloys.

Material	Composition by mass	Density in g/cm³	Strength
pure aluminium	100% Al	2.70	low
alloy P	93.5% Al, 4.4% Cu, 1.5% Mg, 0.6% Mn	2.78	high
alloy Q	95.0% Al, 5.0% Mg	2.64	medium
brass	70% Cu, 30% Zn	8.53	medium

(a) Use the table to give one reason why alloy P is used for aircraft wings rather than brass. [1]

(b) An aircraft wing contains 450 kg of alloy P.

Calculate the mass of copper in the wing. [2]

Explain why aluminium does not corrode away. [2]

(a) (alloy P has a) lower density (2.78 g/cm³ compared with 8.53 g/cm³) so the wing is lighter or alloy P is stronger (high strength compared with medium for brass) allow less dense; allow higher strength(1)
(b) $\dfrac{4.4}{100} \times 450$(1)
(b) 19.8 (kg) allow 20 (kg); correct answer scores 2 marks(1)
(c) aluminium has a (thin) layer of aluminium oxide on its surface allow oxide coating / layer forms when it reacts with oxygen(1)
(c) the oxide layer stops air / oxygen / water reaching the aluminium underneath so no further reaction / corrosion do not accept the layer is paint or grease(1)
Answer: (a) lower density (2.78 vs 8.53 g/cm³), so lighter – or higher strength (high vs medium); (b) 19.8 kg; (c) a layer of aluminium oxide forms on the surface, which stops oxygen and water reaching the metal so it does not corrode further
Examiner tip: In (c) the key word is ‘oxide’ – a protective layer of aluminium oxide, not paint or a coating someone added.

6Grade 6–7HigherTriple only5 marks

Steel is mainly iron. The list shows some metals in order of reactivity.

magnesium (most reactive)
zinc
iron
tin
copper (least reactive)

Steel buckets are coated with zinc (galvanised). Steel food cans are coated with tin.

Both coatings are scratched so that some of the steel underneath is exposed to air and water.

The steel at the scratch on the bucket does not rust. The steel at the scratch on the food can rusts quickly.

(a) Explain these observations. [4]

(b) Complete the half equation for the zinc in the coating when it protects the steel. [1]

$$\text{Zn} \rightarrow \underline{\qquad\qquad}$$

(a) (before scratching) both coatings act as a barrier that keeps air / oxygen and water away from the iron(1)
(a) zinc is more reactive than iron(1)
(a) so zinc reacts / corrodes / is oxidised instead of the iron or sacrificial protection allow zinc loses electrons more easily than iron; do not accept zinc rusts(1)
(a) tin is less reactive than iron so (once scratched) the iron reacts instead / tin gives no sacrificial protection allow tin only works as a barrier(1)
(b) $\text{Zn} \rightarrow \text{Zn}^{2+} + 2\text{e}^-$ allow Zn − 2e⁻ → Zn²⁺; ignore state symbols(1)
Answer: (a) both coatings are barriers; zinc is more reactive than iron so it corrodes instead (sacrificial protection); tin is less reactive than iron so once scratched the iron corrodes; (b) Zn → Zn²⁺ + 2e⁻
Examiner tip: Only iron ‘rusts’ – say zinc corrodes or is oxidised, and compare each coating’s reactivity with iron, not with each other.

7Grade 4–5Triple only6 marks

The table gives information about two types of glass.

Type of glass	Raw materials	Temperature at which the glass softens in °C
soda-lime glass	sand, sodium carbonate and limestone	720
borosilicate glass	sand and boron trioxide	820

(a) Laboratory test tubes are made of borosilicate glass. Test tubes are often heated strongly.

Explain why borosilicate glass is better than soda-lime glass for making test tubes. Use the table. [2]

(b) Calculate the percentage increase in the softening temperature from soda-lime glass to borosilicate glass.

Give your answer to 2 significant figures. [2]

(a) borosilicate glass softens / melts at a higher temperature (820 °C compared with 720 °C) allow 100 °C higher(1)
(a) so it does not soften / change shape / melt when the test tube is heated (strongly) allow soda-lime glass would soften at a lower temperature(1)
(b) $\dfrac{820-720}{720} \times 100$ allow 100 ÷ 720 × 100(1)
(b) 14 (%) correct answer to 2 s.f. scores 2 marks; 13.9 or 13.888… (not to 2 s.f.) scores 1 mark only(1)
(c) wet clay is shaped (e.g. in a mould) allow clay mixed with water and moulded(1)
(c) (then) heated in a furnace / kiln allow fired / baked at a high temperature; ignore heated on its own(1)
Answer: (a) borosilicate softens at a higher temperature (820 °C vs 720 °C) so it keeps its shape when heated; (b) 14%; (c) shape wet clay, then heat it in a furnace
Examiner tip: Percentage increase divides by the ORIGINAL value (720), not the new one – 100 ÷ 820 gives 12%, which scores nothing.

8Grade 6–7Triple only6 marks

The diagram shows the structures of two polymers, X and Y.

(a) Which polymer, X or Y, is a thermosetting polymer? Give a reason from the diagram. [1]

(b) Polymer X softens and melts when heated. Polymer Y does not melt when heated.

Explain why. [3]

Give one way the production of LD poly(ethene) is different from the production of HD poly(ethene). [1]

(d) The table gives information about the two types of poly(ethene).

Polymer	Density in g/cm³	Temperature at which it softens in °C
LD poly(ethene)	0.92	85
HD poly(ethene)	0.96	125

A baby-bottle maker sterilises the bottles in boiling water at 100 °C.

Which type of poly(ethene) should be used to make the bottles? Give a reason. [1]

(a) Y and it has cross-links / links between the chains allow bonds between the chains(1)
(b) (in X) there are (only) weak intermolecular forces between the chains(1)
(b) (in X) these forces are overcome / broken by heating so the chains can slide / move past each other allow little energy needed to overcome the forces(1)
(b) (in Y) the cross-links are (strong covalent) bonds which are not broken when heated so the chains cannot move do not accept intermolecular forces are covalent bonds(1)
(c) different catalyst or different reaction conditions (e.g. temperature / pressure) allow LD made at higher pressure; ignore different monomer(1)
(d) HD poly(ethene) and it softens at 125 °C which is above 100 °C (so it will not soften / lose its shape in boiling water) allow LD would soften at 85 °C(1)
Answer: (a) Y – cross-links between chains; (b) X has weak intermolecular forces that are overcome so chains slide; Y’s cross-links are strong bonds not broken by heating; (c) different catalyst / conditions; (d) HD – softens at 125 °C, above 100 °C
Examiner tip: Heating a thermosoftening polymer overcomes the forces BETWEEN chains – never write that the covalent bonds in the chains break.

9Grade 6–7Triple only6 marks

A company is choosing a material to make the frame of a racing bicycle. The table gives information about three materials.

Material	Density in g/cm³	Strength in MPa	Relative cost	Other information
low carbon steel	7.85	400	low	rusts unless painted; easy to repair by welding
aluminium alloy	2.70	310	medium	does not corrode away
carbon fibre composite	1.55	900	very high	carbon fibres in a polymer resin; does not corrode; can crack if hit hard and is difficult to repair

Evaluate the use of the three materials for the frame of a racing bicycle.

Use the information in the table and your knowledge of the materials.

Give a justified conclusion. [6]

racing frame needs to be light (low density / low mass) and strong(1)
carbon fibre composite has the lowest density (1.55 g/cm³) so lightest frame – about 5 times less dense than steel(1)
carbon fibre composite is strongest (900 MPa) – over twice as strong as steel and about 3 times aluminium alloy(1)
composite: carbon fibres are the reinforcement held in a polymer resin matrix / binder, combining the properties of both(1)
composite: very high cost / cracks if hit / hard to repair(1)
steel is strong (400 MPa) and cheapest but has the highest density so the frame is heaviest(1)
steel rusts – needs a barrier such as paint (adds cost/mass; rusts if paint is scratched); low carbon steel is easily shaped / repaired(1)
aluminium alloy is about one third the density of steel (2.70 vs 7.85) so a much lighter frame, but less strong (310 MPa) so tubes may need to be thicker(1)
aluminium does not corrode away because of its protective aluminium oxide layer(1)
quantitative comparison, e.g. strength ÷ density: steel ≈ 51, aluminium alloy ≈ 115, composite ≈ 580(1)
justified conclusion, e.g. carbon fibre composite because a racing bike needs the lightest, strongest frame and cost matters less; or aluminium alloy as a lighter, corrosion-resistant compromise if cost matters; any conclusion allowed if justified by comparison(1)

Level	Marks	What it looks like
Level 3	5–6	A detailed, coherent evaluation of all three materials, using data from the table to compare density, strength, cost and corrosion (ideally with a quantitative comparison) and linking at least one property to structure or chemistry (e.g. oxide layer, composite matrix and reinforcement). Gives a conclusion clearly justified by the comparison.
Level 2	3–4	Compares at least two materials, with some use of data, giving advantages and disadvantages linked to use in a racing frame. A conclusion is given but may be only partly justified.
Level 1	1–2	Simple statements about one or more materials, mostly copied from the table, with little or no comparison. Any conclusion is not justified.
No relevant content	0	Nothing worthy of credit.

Answer: Carbon fibre composite: lowest density and highest strength (best for racing) but very expensive and hard to repair; aluminium alloy a lighter, corrosion-resistant compromise; steel cheapest and repairable but heaviest and rusts. Justified conclusion, e.g. composite for a racing bike.
Examiner tip: A top-level answer compares all three with numbers from the table and ends with a conclusion that says WHY that material beats the other two.

10Grade 8–9HigherTriple only7 marks

A student used the apparatus shown to find the percentage of oxygen in air.

At the start, the cylinder contained 85.0 cm³ of air. After one week the volume of gas in the cylinder had stopped changing at 67.2 cm³. The iron wool had rusted.

(a) Explain why the water level inside the measuring cylinder rose. [2]

(b) Calculate the percentage of oxygen in the air. Give your answer to 3 significant figures. [2]

$$4\text{Fe} + 3\text{O}_2 \rightarrow 2\text{Fe}_2\text{O}_3$$

Calculate the mass of iron that reacted.

The volume of one mole of any gas at room temperature and pressure is 24.0 dm³.

Relative atomic mass ($A_r$): Fe = 56

Give your answer to 3 significant figures. [3]

(a) iron reacts with the oxygen (in the air) / rusts using oxygen(1)
(a) so the volume of gas (in the cylinder) decreases and water rises to take its place allow oxygen is used up so pressure inside falls(1)
(b) volume of oxygen = 85.0 − 67.2 = 17.8 (cm³)(1)
(b) $\dfrac{17.8}{85.0} \times 100 = 20.9$ (%) allow 20.94…; correct answer scores 2 marks(1)
(c) moles of oxygen = $\dfrac{17.8}{24\,000}$ = 7.42 × 10⁻⁴ (mol) allow 0.0178 ÷ 24; allow ECF from volume in (b)(1)
(c) moles of iron = $7.42\times10^{-4} \times \dfrac{4}{3}$ = 9.89 × 10⁻⁴ (mol)(1)
(c) mass of iron = 9.89 × 10⁻⁴ × 56 = 0.0554 (g) allow 5.54 × 10⁻² g; allow ECF; correct answer to 3 s.f. scores 3 marks; 0.0312 g (mole ratio used as 3/4) scores 2 marks(1)
Answer: (a) iron reacts with (uses up) the oxygen, so the gas volume falls and water rises to replace it; (b) 20.9%; (c) 0.0554 g
Examiner tip: Convert cm³ to dm³ (÷ 1000) before dividing by 24, and use the 4 : 3 ratio the right way round – more iron than oxygen.

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