Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):
• Topic 4.1 — Electrolysis (Parts (a), (b), (c), (d), (e)(i), (e)(ii))
• Topic 7.3 — Preparation of salts (Part (f) related to hydrated substances)
(a)
LHS electrode labelled ‘anode’
In electroplating, the object to be plated is the cathode (negative electrode). The plating metal (copper) is the anode (positive electrode), which dissolves to replace the metal ions in the solution. The LHS electrode is the positive anode.
(b)
Any soluble copper salt (e.g. copper(II) sulfate)
The electrolyte must contain the metal ions to be plated. A solution of a soluble copper salt, like copper(II) sulfate, provides the necessary \( \mathrm{Cu}^{2+} \) ions.
(c)
Red-brown
Electrolysis of molten lead(II) bromide produces bromine gas at the anode. Bromine is a red-brown gas/vapour.
(d)
Type of change: chemical
Explanation: New substance(s) made
Electrolysis decomposes a compound (lead(II) bromide) into its elements (lead and bromine). Since new chemical substances are formed, this is a chemical change.
(e)(i)
Ethanoic acid
This answer corresponds to a related question regarding the oxidation of ethanol: the product formed is ethanoic acid.
(e)(ii)
Lighted splint AND ‘pop’ sound
The ‘pop’ sound with a lighted splint is the standard test for hydrogen gas.
(f)
Hydrated means chemically bonded to water molecules, anhydrous means containing no water, and aqueous means dissolved in water to form a solution.
