A student has collected a sample of muddy river water. Describe how the processes of sedimentation and filtration can be used to remove the solid particles from this water sample.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
River water often contains suspended solid particles such as sand and mud. These solids must be removed as part of water treatment before the water can become potable.
Model answer (4 marks)
Sedimentation:
1. Leave the muddy water undisturbed in a clear container.
2. Suspended solids settle by gravity to form a sediment at the bottom.
3. The clear water above the sediment can then be decanted or siphoned off.
Filtration:
4. The remaining water is passed through a filter (e.g. filter paper or cloth).
5. The filter traps the remaining insoluble particles, forming a residue.
6. The clean water (filtrate) passes through the filter and can be collected.
1. Leave the muddy water undisturbed in a clear container.
2. Suspended solids settle by gravity to form a sediment at the bottom.
3. The clear water above the sediment can then be decanted or siphoned off.
Filtration:
4. The remaining water is passed through a filter (e.g. filter paper or cloth).
5. The filter traps the remaining insoluble particles, forming a residue.
6. The clean water (filtrate) passes through the filter and can be collected.
Examiner tips
- Use the word ‘sedimentation’ first, then explain gravity‑settling. Show that the sediment is removed before filtration. Mention that filtration separates the remaining solids by trapping them in the filter. Use the terms ‘filter’, ‘residue’ and ‘filtrate’ as the mark scheme expects.
Common mistakes
- Confusing sedimentation with filtration or vice versa. Failing to mention that the sediment is removed before filtration. Using vague terms like ‘clean water’ instead of ‘filtrate’ or ‘filter’.”
Mark scheme (4 marks)
- Sedimentation involves leaving the water so that suspended solids fall to the bottom of the container (forming a sediment)
- Sedimentation allows the solid particles to be easily removed from the water
- Filtration is used to separate the remaining insoluble solid particles from the water / the water passes through a filter
- The solid particles are trapped / remain in the filter (as a residue) and the water passes through as the filtrate
Key terms in this question
Related
- All Edexcel GCSE Chemistry (1CH0) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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