2019 O Level Chem P1 Q29 — Metals / Extraction of Metals Solution

Answer: A (copper). Two conditions must both be satisfied. First, M can be obtained from its oxide by heating with carbon, which works only for metals less reactive than carbon — such as zinc, iron, lead and copper. Second, M can be obtained from its aqueous chloride by electrolysis, which deposits the metal at the cathode only if the metal is less reactive than hydrogen, so that the metal ion is discharged in preference to H⁺ from water.

Copper meets both: \(\text{CuO} + \text{C} \to \text{Cu} + \text{CO}\), and during electrolysis of aqueous copper(II) chloride, \(\text{Cu}^{2+} + 2\text{e}^- \to \text{Cu}\) at the cathode.

Sodium is far too reactive: carbon cannot reduce its oxide and electrolysing its aqueous chloride gives hydrogen at the cathode, not sodium. Silver is so unreactive its oxide decomposes on heating alone, and lead sits awkwardly close to hydrogen. Copper is the clear-cut answer, so A.