CIE iGCSE Co-Ordinated Science C10.2 Air quality and climate Exam Style Questions Paper 3
Question
Most-appropriate topic codes (Cambridge IGCSE Coordinated Sciences 0654):
• Topic C11.4 — Alkanes (Part (a))
• Topic C11.2 — Naming organic compounds (Part (b))
• Topic C3.2 — Relative masses of atoms and molecules (Part (c))
• Topic C10.1 — Water (Part (d)(i))
• Topic C10.1 — Water (Part (d)(ii))
• Topic C10.2 — Air quality and climate (Part (d)(iii))
▶️ Answer/Explanation
(a) single and double
Alkanes have only single C-C bonds, so they are saturated (cannot add more atoms). Alkenes have at least one C=C double bond, making them unsaturated and able to undergo addition reactions.
(b) Displayed formula of ethane with C-C single bond and all C-H bonds correct
Ethane (C₂H₆) has two carbon atoms joined by a single bond, with each carbon bonded to three hydrogen atoms. The displayed formula shows all atoms and bonds.
(c) 24 + 6 or 2 × 12 + 6 × 1; 30
Mᵣ of C₂H₆ = (2 × 12) + (6 × 1) = 24 + 6 = 30. Relative molecular mass is the sum of the relative atomic masses of all atoms in the molecule.
(d)(i) blue; (to) pink
Anhydrous cobalt(II) chloride is blue. When water is present, it turns pink as it forms hydrated cobalt(II) chloride. This is a positive test for water.
(d)(ii) pure water boils at 100°C; impurities increase boiling point
Pure water has a boiling point of 100°C at standard atmospheric pressure. The observed boiling point of 102°C is higher than 100°C, indicating the presence of impurities that elevate the boiling point.
(d)(iii) planting trees / planting plants; CO₂ removed by trees / CO₂ removed by plants
OR decreasing use of fossil fuels; less CO₂ produced (during combustion)
OR increasing use of renewables; no CO₂ produced
Plants absorb CO₂ during photosynthesis, reducing atmospheric CO₂. Reducing fossil fuel use decreases CO₂ emissions at source.
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.