2024 O Level Chem P1 Q2 — Metal Extraction / Identification of Gases Solution
Question
A scientist investigates the products of the reaction between lead(II) oxide and carbon monoxide. Carbon monoxide, like carbon, is able to reduce metal oxides. Which reagent and set of apparatus allows the scientist to identify the gaseous product and prevents excess carbon monoxide from entering the atmosphere?
Correct answer: C
Video Solution
Explanation
Answer: C. The reduction is \(\text{PbO} + \text{CO} \rightarrow \text{Pb} + \text{CO}_2\). Two requirements: identify the gaseous product, AND prevent excess CO escaping into the atmosphere.
Limewater identifies \(\text{CO}_2\) (turns milky → confirms reduction occurred). Collection of remaining gas over water in a downstream vessel traps any unreacted CO so it can't vent.
A uses concentrated sulfuric acid, which doesn't test for \(\text{CO}_2\). B has limewater but no second trap, so excess CO bubbles through and escapes. D applies limewater only at the final stage, after CO has already passed through earlier collection points.
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