CIE iGCSE Co-Ordinated Science C9.5 Corrosion of metals Exam Style Questions Paper 3
Question
Most-appropriate topic codes (Cambridge IGCSE Coordinated Sciences 0654):
• Topic C10.2 — Air quality and climate (Part (a)(i)-(iv))
• Topic C9.5 — Corrosion of metals (Part (a)(v))
• Topic C2.5 — Simple molecules and covalent bonds (Part (b))
• Topic C7.1 — Characteristic properties of acids (Part (c))
• Topic C4.2 — Hydrogen-oxygen fuel cells (Part (d))
▶️ Answer/Explanation
(a)(i) He
Helium (He) is a monatomic gas because it consists of single atoms rather than molecules. It is a noble gas with a full outer electron shell.
(a)(ii) CO
Carbon monoxide (CO) is a toxic gas produced by incomplete combustion. It binds to haemoglobin in red blood cells, preventing oxygen transport.
(a)(iii) N₂
Nitrogen (N₂) makes up approximately 78% of clean, dry air. It is an inert gas at normal temperatures.
(a)(iv) He or N₂ or O₂
Elements are substances that contain only one type of atom. He, N₂, and O₂ are all elements, while CO, CO₂, and H₂O are compounds.
(a)(v) O₂ and H₂O
Rusting of iron requires both oxygen (O₂) and water (H₂O). These react with iron to form hydrated iron(III) oxide.
(b) Shared pair correct; all else correct
In HCl, hydrogen shares one electron with chlorine to complete both their outer shells. The dot-and-cross diagram should show one shared pair of electrons.
(c) turns red
Dilute hydrochloric acid is acidic. Acids turn blue litmus paper red, indicating a pH below 7.
(d) hydrogen; oxygen
A hydrogen-oxygen fuel cell uses hydrogen and oxygen as reactants. The chemical energy is converted directly into electrical energy with water as the only product.
Question
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C9.6 — Extraction of metals (Part (a))
• Topic C9.5 — Corrosion of metals (Part (b))
• Topic C9.1 — Properties of metals (Part (c)(i))
• Topic C7.1 — The characteristic properties of acids and bases (Part (c)(ii))
• Topic C9.1 — Properties of metals (Part (d))
▶️ Answer/Explanation
(a)(i) Reduction is the loss of oxygen from a substance.
In the blast furnace, iron(III) oxide is reduced by carbon monoxide to produce iron metal. The iron(III) oxide loses oxygen to become iron.
(a)(ii) Hematite
Hematite is the main ore of iron used in the blast furnace. Its chemical formula is Fe₂O₃ (iron(III) oxide).
(b) oxygen and water
Rusting of iron requires both oxygen (from the air) and water to be present. If either is absent, rusting does not occur.
(c)(i) Iron forms a coloured compound (pale green iron(II) chloride).
Transition metals are characterised by forming coloured compounds. The pale green colour of iron(II) chloride indicates that iron is a transition metal.
(c)(ii) Fe(s) + 2HCl(aq) → FeCl₂(aq) + H₂(g)
The equation is balanced with 2 moles of HCl reacting with 1 mole of iron. The state symbols are: (s) for solid iron, (aq) for aqueous hydrochloric acid and iron(II) chloride, and (g) for hydrogen gas.
(d) High melting/boiling point / malleable / ductile
Most metals have characteristic physical properties including high melting and boiling points, malleability (can be hammered into shapes), and ductility (can be drawn into wires). Any one of these is correct.