Lithium, sodium and potassium are all stored under oil in the laboratory. Explain why these metals must be stored in this way.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Group I metals are kept submerged in oil when stored in a laboratory. They are soft, low-density metals that react readily with substances found in the surrounding environment.
Model answer (4 marks)
Lithium, sodium and potassium are highly reactive alkali metals. They react rapidly with the oxygen in air to form a surface oxide layer and with the water vapour (moisture) in the atmosphere to give hydroxide and hydrogen gas. The reactions are vigorous and can be dangerous. Oil provides a physical barrier that prevents contact with air and moisture, so the metals are not consumed and remain safe for use.
Examiner tips
- Use the word ‘react’ and specify oxygen and water vapour; mention the barrier function of oil; explain the safety reason; keep answer concise to fit 4 marks
Common mistakes
- Forgetting to mention water vapour; describing oil as ‘lubricant’ instead of barrier; over‑expanding with unrelated properties of alkali metals
Mark scheme (4 marks)
- Group I metals react with oxygen / air
- Group I metals react with water (vapour / moisture in the air)
- Oil acts as a barrier / prevents contact with air and water / moisture
- To prevent the metals from being used up / to keep them safe / reactions could be dangerous / vigorous
Related
- All Cambridge International IGCSE Chemistry (0620) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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