A list of gases is shown.
Answer the following questions about these gases. Each gas may be used once, more than once or not at all.
(a) State one gas which:
(i) is the main constituent of natural gas
(ii) is responsible for both photochemical smog and acid rain
(iii) is unsaturated
(iv) has monatomic particles
(v) reduces iron(III) oxide in a blast furnace.
(b) Nitrogen dioxide, \(NO_2\), and carbon monoxide are removed from a car exhaust by a catalytic converter. Write the symbol equation for this reaction.
Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):
• Topic 11.3 — Fuels (a)(i)
• Topic 10.3 — Air quality and climate (a)(ii)
• Topic 11.5 — Alkenes (a)(iii)
• Topic 8.5 — Noble gases (a)(iv)
• Topic 9.6 — Extraction of metals (a)(v)
• Topic 10.3 — Air quality and climate (b)
Detailed Solution:
(a)(i) Methane: According to the syllabus (Topic 11.3), natural gas is a fossil fuel, and methane (CH₄) is named as its main constituent.
(a)(ii) Nitrogen dioxide: The syllabus (Topic 10.3) states that oxides of nitrogen from car engines cause photochemical smog and, as they dissolve in water to form acids, are also responsible for acid rain.
(a)(iii) Propene: Unsaturated hydrocarbons contain at least one carbon-carbon double bond (C=C). According to the diagram, propene (C₃H₆) fits the general formula CₙH₂ₙ for alkenes, which are unsaturated (Topic 11.5).
(a)(iv) Helium: Noble gases (Group VIII) exist as single, separate atoms (monatomic) due to their full outer electron shell, which makes them unreactive (Topic 8.5).
(a)(v) Carbon monoxide: In the blast furnace extraction of iron (Topic 9.6), carbon monoxide (CO) acts as the reducing agent. It reacts with and removes oxygen from iron(III) oxide (Fe₂O₃).
(b) 2NO₂ + 4CO → N₂ + 4CO₂: The syllabus (Topic 10.3 Supplement) requires knowledge of how catalytic converters remove oxides of nitrogen. They convert harmful NO and NO₂ into harmless nitrogen gas (N₂) while also converting toxic carbon monoxide (CO) into carbon dioxide (CO₂).
