When silver nitrate solution is added to sodium chloride solution, a white solid forms immediately and the solution becomes cloudy. Explain why this is a chemical change rather than a physical change.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Silver nitrate solution and sodium chloride solution are both colourless liquids. When they are mixed, a white solid forms that cannot be separated back into silver nitrate and sodium chloride by filtering alone.
Model answer (4 marks)
A new substance, silver chloride, is produced.
The reaction is irreversible – the solid cannot be recovered as silver nitrate and sodium chloride.
In a physical change no new substance is formed and the original material keeps its properties.
The products have different properties (white solid, cloudy solution) from the reactants, indicating a chemical reaction.
The reaction is irreversible – the solid cannot be recovered as silver nitrate and sodium chloride.
In a physical change no new substance is formed and the original material keeps its properties.
The products have different properties (white solid, cloudy solution) from the reactants, indicating a chemical reaction.
Examiner tips
- Use the word ‘new substance’ to show a chemical change. Mention irreversibility to contrast with a reversible physical change. Highlight the change in appearance (white solid, cloudiness). Keep each point concise and directly linked to the mark scheme.
Common mistakes
- Saying the change is ‘fast’ or ‘instantaneous’ – this does not prove a chemical change. Confusing the formation of a precipitate with a physical separation. Forgetting to state that the new substance cannot be returned to the original reactants.
Mark scheme (4 marks)
- A new substance (silver chloride) is formed
- The change is irreversible / cannot be easily reversed
- In a physical change, no new substance is formed / the substance keeps its original properties
- The properties of the products are different from the reactants, showing a chemical reaction has occurred
Key terms in this question
chemical change · physical change
Related
- All Eduqas GCSE Chemistry revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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