1. 1
   A student mixes silver nitrate solution with sodium chloride solution in a test tube. A white solid (silver chloride) forms immediately and settles at the bottom, leaving a solution of sodium nitrate above it.

   (a)

   Silver chloride does not dissolve in water. What name is given to this type of reaction?

   [1 mark]

   • AA precipitation reaction
   • BA neutralisation reaction
   • CA combustion reaction
   • DA displacement reaction

   (b)

   Which solution provides the chloride ions needed to form the insoluble silver chloride precipitate?

   [1 mark]

   • ASilver nitrate solution
   • BSodium chloride solution
   • CSodium nitrate solution
   • DDistilled water

   (c)

   Describe how the student should separate the solid silver chloride precipitate from the remaining sodium nitrate solution, and obtain a dry sample of the salt.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A water treatment plant adds iron(III) chloride solution to wastewater containing dissolved phosphate ions. This causes insoluble iron phosphate to form as a precipitate, which settles out and is removed before the treated water is released into a river.

   (a)

   Why is this method used before the water is released into a river?

   [1 mark]

   • ATo add more chloride ions to the river
   • BTo make the water taste better
   • CTo increase the pH of the wastewater
   • DTo remove phosphate ions, which can cause excessive algal growth in the river if released

   (b)

   What happens to the phosphate ions during this precipitation reaction?

   [1 mark]

   • AThey are converted into chloride ions
   • BThey evaporate out of the water as a gas
   • CThey combine with iron ions to form an insoluble solid that can be removed from the water
   • DThey remain dissolved in the water, unchanged

   (c)

   Explain how this precipitation process removes the unwanted phosphate ions from the wastewater before it is released into the river.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student wants to prepare a pure dry sample of lead iodide, an insoluble bright yellow salt, in a school laboratory.

   (a)

   A student wants to prepare a sample of lead iodide, an insoluble bright yellow salt. Name the two solutions the student should mix, and describe what will be observed.

   [3 marks]

   (b)

   Describe how the student obtains a pure, dry sample of solid lead iodide from the mixture.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A local council is treating water supplies to remove unwanted dissolved ions before the water is used or released into the environment. One task is to remove excess fluoride ions from drinking water using calcium chloride solution. Another task is to remove phosphate ions from effluent before it reaches a nearby lake, to prevent excessive algal growth.

   (a)

   A local council needs to remove excess dissolved fluoride ions from a supply of drinking water by adding calcium chloride solution, which reacts with the fluoride ions to form insoluble calcium fluoride. Describe, in full, how this precipitation reaction could be carried out and how the solid calcium fluoride could be obtained and removed from the water.

   [6 marks]

   (b)

   Evaluate the advantages and possible limitations of using precipitation reactions, as described above, to remove unwanted ions from drinking water or effluent before it is released into the environment.

   [6 marks]

   Total for question 4: 12 marks

End of questions