1. 1
   A student finds an unlabelled clear liquid in a laboratory and wants to confirm whether it contains water before continuing an experiment. She adds a few drops of the liquid to a sample of white anhydrous copper(II) sulfate powder.

   (a)

   Which colour change would confirm that water is present in the liquid?

   [1 mark]

   • AWhite to blue
   • BBlue to white
   • CBlue to pink
   • DPink to blue

   (b)

   The student also has a sample of anhydrous cobalt(II) chloride paper available. Which colour change in this paper would confirm the presence of water?

   [1 mark]

   • AWhite to blue
   • BBlue to pink
   • CPink to blue
   • DBlue to white

   (c)

   Having confirmed the liquid contains water, the student wants to check whether it is pure water or water containing dissolved impurities. Describe two physical measurements she could carry out on the liquid to test its purity, and state what result would indicate the water is pure in each case.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A chemistry technician preparing standard solutions for a school laboratory is deciding whether to use tap water or distilled water. She chooses distilled water for all quantitative practical work.

   (a)

   What is the main reason distilled water is preferred over tap water in this context?

   [1 mark]

   • ADistilled water is cheaper to produce than tap water
   • BDistilled water has a higher boiling point than tap water
   • CDistilled water contains fewer chemical impurities than tap water
   • DDistilled water contains added chlorine for disinfection

   (b)

   The technician also supervises a project studying a river near a farm that drains into a public reservoir used for the town's tap water supply. Fertiliser runoff from the farm has increased the nitrate and phosphate levels in the river. What is the main environmental consequence of these increased nitrate and phosphate levels in the water?

   [1 mark]

   • AA reduction in harmful microbes in the water
   • BAn increase in dissolved oxygen benefiting aquatic life
   • CA decrease in the water's electrical conductivity
   • DEutrophication, causing excessive algal growth

   (c)

   Explain one beneficial and one potentially harmful effect that substances dissolved in natural water sources, such as the river described, can have.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A water company operates a treatment works that takes water from the reservoir described above (affected by fertiliser runoff and general debris) and treats it before it is supplied to homes as drinking water.

   (a)

   Describe the sedimentation and filtration stages of this treatment process, and state what type of impurity each stage is designed to remove.

   [3 marks]

   (b)

   After sedimentation and filtration, the water still has an earthy taste and odour, and could still contain harmful microbes from the farm runoff. Describe the two further treatment stages needed to address these two remaining problems, explaining what each stage achieves.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A public health officer is preparing a report on why a rural community's traditional practice of drinking untreated river water has led to repeated outbreaks of disease, and why building a modern water treatment works would resolve the problem.

   (a)

   Discuss the substances that may be present in the untreated river water (including dissolved oxygen, metal compounds, nitrates, phosphates and harmful microbes), and the beneficial or harmful effects of each, before explaining how a full treatment process would address the harmful ones.

   [6 marks]

   (b)

   The officer also wants to explain, for a non-specialist audience, how the community could quickly check at home whether water collected from a new well is likely to be pure enough to trust, using simple chemical and physical tests, before the treatment works is completed. Describe the chemical tests for the presence of water and the physical tests for the purity of water that could be used, and explain the limitations of relying on these simple tests alone.

   [6 marks]

   Total for question 4: 12 marks

End of questions