Explain why some metals are found as native metals in the Earth's crust whilst others must be extracted from their ores.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Metals vary in their reactivity. Gold and platinum are found as uncombined elements in nature, whilst metals such as zinc and iron are always found as compounds.
Model answer (4 marks)
Unreactive metals such as gold and platinum are found as native metals because they do not react readily with other elements in the Earth's crust.
More reactive metals, for example zinc and iron, are found as compounds (oxides, sulfides, etc.) because they readily react with oxygen, sulphur and other elements.
To obtain a pure metal from its ore, a more reactive substance (e.g. carbon or an electric current) must reduce the metal ion.
Thus the position of a metal in the reactivity series determines whether it is found as a native metal or as an ore and which extraction method is required.
More reactive metals, for example zinc and iron, are found as compounds (oxides, sulfides, etc.) because they readily react with oxygen, sulphur and other elements.
To obtain a pure metal from its ore, a more reactive substance (e.g. carbon or an electric current) must reduce the metal ion.
Thus the position of a metal in the reactivity series determines whether it is found as a native metal or as an ore and which extraction method is required.
Examiner tips
- Use the terms "native metal" and "ore". Mention the reactivity series. Explain the need for a reducing agent or electrolysis for reactive metals.
Common mistakes
- Confusing the terms native metal and ore. Failing to link reactivity to the need for reduction. Using vague phrases like "reactive" without reference to the series.
Mark scheme (4 marks)
- Unreactive / less reactive metals are found as native / uncombined metals
- More reactive metals are found as compounds / ores because they react readily with other elements (e.g. oxygen, sulfur)
- Metals above carbon / hydrogen in the reactivity series require reduction by a more reactive substance (e.g. carbon / electrolysis) to extract them
- The position of a metal in the reactivity series determines the method of extraction used
Key terms in this question
Related
- All Cambridge International IGCSE Chemistry (0620) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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