WJEC GCSE Chemistry 2.3 Metals and Their Extraction Exam Questions

About WJEC GCSE Chemistry 2.3 Metals and Their Extraction

Metals and their extraction in Unit 2 links reactivity to how metals are obtained from their ores. You need the reactivity series and displacement reactions, the reduction of iron oxide in the blast furnace, and the extraction of aluminium by electrolysis. You must explain electrolysis in terms of ions moving to electrodes, write half equations, and describe the electrolysis of water and aqueous solutions. Properties and uses of metals, transition metals and alloys are covered, along with the economics and benefits of recycling. Specified practicals cover displacement reactions and electrolysis. Examiners often ask why aluminium is extracted by electrolysis but iron by carbon.

What you need to know

• Reactivity and ores Ores are rocks containing enough metal compound to make extraction worthwhile. A more reactive metal displaces a less reactive one from its compounds, e.g. Mg + CuSO4 → MgSO4 + Cu. Metals below carbon can be extracted by heating with carbon.
• Blast furnace Coke burns: C + O2 → CO2, then CO2 + C → 2CO. Carbon monoxide reduces iron(III) oxide: Fe2O3 + 3CO → 2Fe + 3CO2. Limestone decomposes and the calcium oxide reacts with sand impurities to form slag.
• Electrolysis Ionic substances that are molten or in solution conduct; positive ions move to the cathode and gain electrons, negative ions move to the anode and lose electrons. Electrolysis is a specified practical, e.g. of copper(II) chloride solution.
• Aluminium Aluminium is more reactive than carbon, so aluminium oxide is electrolysed, dissolved in molten cryolite to lower the operating temperature. At the cathode Al3+ + 3e- → Al; at the anode oxide ions form oxygen, which burns the carbon anodes, so they must be replaced.
• Transition metals and alloys Transition metals are dense, have high melting points, form coloured compounds and act as catalysts. Alloys such as steel are harder than pure metals because different sized atoms distort the layers so they cannot slide easily.
• Recycling Recycling metals saves ore and energy, reduces mining and landfill and is often cheaper, but requires collection and sorting. Extraction by electrolysis is expensive because of the large amount of electricity used.

Common mistakes in 2.3 Metals and Their Extraction

• Saying aluminium is extracted by electrolysis because it is a strong metal. It is too reactive to be reduced by carbon.
• Writing that oxygen is the reducing agent in the blast furnace. Carbon monoxide reduces iron(III) oxide by removing oxygen.
• Mixing up which ions go to which electrode. Positive ions (cations) go to the negative cathode; negative ions (anions) go to the positive anode.
• Explaining that alloys are stronger because they are mixed. Explain that different sized atoms disrupt the regular layers, so layers cannot slide as easily.

Try three 2.3 Metals and Their Extraction exam-style questions