1. 1
   A student is given four unlabelled aqueous solutions, W, X, Y and Z, as part of a class investigation into pH. She adds a few drops of universal indicator solution to a sample of each and records the colour produced. Solution W turns the indicator red, solution X turns it green, solution Y turns it purple, and solution Z turns it orange.

   (a)

   A student tests four unlabelled solutions with universal indicator. Solution W turns the indicator red, solution X turns it green, solution Y turns it purple, and solution Z turns it orange. Which solution has the highest concentration of hydrogen ions?

   [1 mark]

   • ASolution W
   • BSolution X
   • CSolution Y
   • DSolution Z

   (b)

   Which indicator would turn yellow in solution Y but a different colour in solution Z?

   [1 mark]

   • ALitmus
   • BMethyl orange
   • CUniversal indicator only
   • DNone of these indicators change colour with pH

   (c)

   Solution Z has a pH of 4 and solution W has a pH of 1. Compare the concentration of hydrogen ions in solution W with that in solution Z, explaining your reasoning.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A technician sets up three test tubes, each containing 20 cm3 of a dilute acid. She adds a different solid or solution to each test tube: magnesium ribbon to tube 1, copper carbonate powder to tube 2, and copper oxide powder to tube 3. She observes the reactions and collects any gas produced over water.

   (a)

   Which pair of reactants would produce a salt, water and carbon dioxide gas only?

   [1 mark]

   • ADilute hydrochloric acid and magnesium ribbon
   • BDilute hydrochloric acid and copper oxide powder
   • CDilute nitric acid and sodium hydroxide solution
   • DDilute sulfuric acid and copper carbonate powder

   (b)

   The technician wants to confirm that the gas collected from tube 2 is carbon dioxide. Which observation would confirm this?

   [1 mark]

   • AThe gas relights a glowing splint
   • BThe gas produces a squeaky pop with a lit splint
   • CThe gas turns limewater cloudy (milky)
   • DThe gas turns damp blue litmus paper red then white

   (c)

   Describe the chemical test the technician should use to confirm the identity of the gas produced in tube 1, and state the expected result.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student is asked to prepare a pure, dry sample of hydrated copper sulfate crystals in the laboratory, starting from copper oxide powder and dilute sulfuric acid, following the core practical method.

   (a)

   Explain why, when preparing a soluble salt from copper oxide (an insoluble base) and dilute sulfuric acid, excess copper oxide is added to the acid rather than mixing the two in exact proportions.

   [3 marks]

   (b)

   Describe the remaining steps the student should carry out, after filtering off the excess copper oxide, to obtain pure, dry hydrated copper sulfate crystals.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A technician mixes a solution of sodium sulfate with a solution of barium chloride, and separately mixes a solution of potassium carbonate with a solution of lead nitrate, as part of a demonstration on predicting precipitation reactions using solubility rules.

   (a)

   Using the solubility rules for common salts, predict and explain, with reference to ions present, whether a precipitate forms in each mixture, name any precipitate formed, and describe how the technician could isolate a pure, dry sample of any insoluble salt produced.

   [6 marks]

   (b)

   The technician then wants to prepare a pure, dry sample of a soluble salt, sodium sulfate, from dilute sulfuric acid and sodium hydroxide solution, both of which are soluble. Explain why the method used for this preparation must differ from the method used for preparing an insoluble salt by precipitation, and describe the full method, including how the technician ensures the correct proportions of acid and alkali are mixed.

   [6 marks]

   Total for question 4: 12 marks

End of questions