CIE iGCSE Co-Ordinated Science C8.4 Transition elements Exam Style Questions Paper 3
Question
☐ copper forms coloured compounds
☐ copper has a low melting point
☐ copper has a low density
☐ copper is ductile
Topic codes:
• Topic C2.2 — Atomic structure and the Periodic Table (Part (a)(i) & (a)(ii))
• Topic C8.4 — Transition elements (Part (b))
• Topic C3.1 — Formulas (Part (c)(i))
• Topic C2.1 — Elements, compounds and mixtures (Part (c)(ii))
• Topic C9.3 — Alloys and their properties (Part (d)(i), (d)(ii) & (d)(iii))
▶️ Answer/Explanation
(a)(i) Proton number (atomic number)
The number 29 is the proton number (also called atomic number) of copper. This is the number of protons in the nucleus of a copper atom. All atoms of the same element have the same proton number.
(a)(ii) 35 neutrons
Number of neutrons = mass number − proton number = 64 − 29 = 35.
The mass number (64) is the total number of protons and neutrons in the nucleus.
(b) The three correct statements are:
✓ copper acts as a catalyst
✓ copper forms coloured compounds
✓ copper is ductile
Transition elements are metals with high densities and high melting points (not low). They form coloured compounds, often act as catalysts, and are ductile (can be drawn into wires).
(c)(i) 2Cu(s) + O₂(g) → 2CuO(s)
The balanced equation shows 2 copper atoms reacting with 1 oxygen molecule to form 2 copper(II) oxide units. This ensures the number of atoms of each element is the same on both sides: 2 Cu on both sides, and 2 O on both sides.
(c)(ii) Gas
The symbol (g) indicates that oxygen is in the gaseous state at room temperature and pressure.
(d)(i) An alloy is a mixture of a metal with other elements.
Alloys are mixtures of metals with other metals or non-metals to enhance specific properties such as strength, hardness, or corrosion resistance.
(d)(ii) Structure Y
Structure Y best represents an alloy because it shows atoms of different sizes arranged in a metallic lattice. In alloys, atoms of different sizes disrupt the regular arrangement of atoms, making it harder for layers to slide over each other, which increases hardness and strength.
(d)(iii) Stainless steel is used in cutlery because of its hardness and resistance to rusting (corrosion).
Stainless steel is an alloy of iron with chromium, nickel, and carbon. It is hard and does not rust easily, making it ideal for knives, forks, and other cutlery items that need to maintain a sharp edge and withstand frequent washing.
Question
(ii) Identify two substances which are solvents.
(iii) Identify one substance which is a transition element.
(iv) Identify one substance which is a halogen.
(v) Identify one substance which consists of diatomic molecules.
Most-appropriate topic codes:
• Topic C1.1 — Solids, liquids and gases (Part (a))
• Topic C8.4 — Transition elements (Part (b))
▶️ Answer/Explanation
(a)
In solids, particles are held tightly together and can only vibrate in place.
In gases, particles are far apart and move freely and randomly.
(b)(i) Water (or ethanol)
A compound contains two or more different elements chemically joined; water \((H_2O)\) is a compound.
(b)(ii) Ethanol and water
Both ethanol and water are common liquids used to dissolve other substances (solvents).
(b)(iii) Copper
Copper is located in the transition metal block of the Periodic Table.
(b)(iv) Chlorine
Chlorine is in Group VII, the halogens.
(b)(v) Chlorine or oxygen
Both chlorine \((Cl_2)\) and oxygen \((O_2)\) exist as diatomic molecules made of two atoms.