The diagram shows a water-treatment investigation at a campsite. Muddy stream water was first passed through a filter containing gravel, sand and charcoal. ...
Question 1 Report
The diagram shows a water-treatment investigation at a campsite. Muddy stream water was first passed through a filter containing gravel, sand and charcoal. The clear liquid was then tested. Table 1 gives results before and after filtration. A student claims that the filtered water is pure water because it looks colourless. The teacher explains that colourless water can still be a solution containing dissolved substances such as sodium chloride or nitrate.
| test | stream water | filtered water |
|---|---|---|
| appearance | brown and cloudy | colourless |
| mass of solid after evaporating 50 cm3 / g | 0.18 | 0.12 |
| nitrate test | positive | positive |
(a) Name the separation process taking place in the filter. [1]
(b) State what happens to insoluble mud particles in this process. [1]
(c) Use Table 1 to explain why the filtered water is not pure. [2]
(d) Give the mass of dissolved solid in 200 cm3 of the filtered water. [2]
(e) Which method could be used to obtain pure water from the filtered water? [1]
(f) Describe one risk of drinking water that contains nitrate ions. [1]
(g) State one limitation of the campsite filter. [1]
(h) Give one reason why charcoal is included in the filter. [2]
Answer Details
(a) The process is filtration. [1]
(b) Insoluble mud particles are trapped by the filter and remain as residue. [1]
(c) The filtered water is not pure because evaporating it leaves solid behind and it still gives a positive nitrate test. A colourless appearance does not prove that dissolved substances are absent. [2]
(d) \(200\text{ cm}^3\) is four times \(50\text{ cm}^3\):
\[0.12\text{ g}\times4=0.48\text{ g}\]
The mass of dissolved solid is 0.48 g. [2]
(e) Use simple distillation to obtain pure water. [1]
(f) Nitrate ions can make water unsafe and may harm health. Nitrates entering waterways can also contribute to eutrophication. [1]
(g) The filter does not remove dissolved salts such as nitrate ions. It may also fail to remove all microorganisms. [1]
(h) Charcoal adsorbs some coloured or smelly dissolved impurities onto its surface, improving the colour or odour of the water. [2]
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