1. 1
   A student tests three household liquids, an oven cleaner, white vinegar, and tap water, by dipping a strip of universal indicator paper into each. The oven cleaner turns the paper dark purple, the vinegar turns it orange-red, and the tap water turns it green.

   (a)

   Which liquid is the most acidic, based on the colour of the indicator, and what pH range does this colour suggest?

   [1 mark]

   • AVinegar; a pH around 3
   • BOven cleaner; a pH around 13
   • CTap water; a pH around 7
   • DOven cleaner; a pH around 3

   (b)

   The oven cleaner turns universal indicator dark purple. What does this indicate about the concentrations of hydrogen ions and hydroxide ions in the oven cleaner?

   [1 mark]

   • AEqual concentrations of hydrogen ions and hydroxide ions
   • BA high concentration of hydroxide ions and a very low concentration of hydrogen ions
   • CA high concentration of hydrogen ions and a very low concentration of hydroxide ions
   • DNo hydrogen ions or hydroxide ions are present

   (c)

   Explain, in terms of ion concentration, why vinegar has a lower pH than tap water.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student adds crushed antacid tablets, which contain calcium carbonate, to a test tube of dilute hydrochloric acid. Bubbles of gas are produced immediately, and the student bubbles this gas through a test tube of limewater, which turns cloudy.

   (a)

   The gas produced turns limewater cloudy. Which gas is being produced in this reaction?

   [1 mark]

   • AHydrogen
   • BOxygen
   • CCarbon dioxide
   • DChlorine

   (b)

   What are the products of the reaction between calcium carbonate and dilute hydrochloric acid?

   [1 mark]

   • ACalcium oxide and carbon dioxide only
   • BCalcium hydroxide and hydrogen
   • CCalcium chloride and oxygen
   • DCalcium chloride, water and carbon dioxide

   (c)

   Write the balanced symbol equation for the reaction between calcium carbonate and hydrochloric acid.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A technician wants to prepare a pure sample of potassium chloride crystals from potassium hydroxide solution (a soluble alkali) and dilute hydrochloric acid, using an acid-alkali titration with a burette, pipette and a suitable indicator.

   (a)

   Explain why titration, rather than simply adding excess acid to a solid, must be used to prepare a pure sample of potassium chloride from potassium hydroxide solution and hydrochloric acid.

   [3 marks]

   (b)

   Describe how the technician would carry out this titration to obtain a pure, dry sample of potassium chloride crystals, including the use of the indicator.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A technician electrolyses dilute sulfuric acid using inert graphite electrodes connected to a direct current supply. Gas bubbles are produced at both electrodes: the volume of gas collected at the negative electrode is twice the volume collected at the positive electrode.

   (a)

   Explain, in terms of the ions present in dilute sulfuric acid, why hydrogen gas is produced at the negative electrode, and describe how you could confirm this gas is hydrogen using a chemical test.

   [6 marks]

   (b)

   Explain why the volume of gas collected at the negative electrode is twice that collected at the positive electrode, referring to the formulae of the gases produced and the process occurring at the positive electrode.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A technician electrolyses molten zinc chloride using inert graphite electrodes connected to a direct current supply. Silvery-grey liquid zinc collects at one electrode, and a greenish-yellow gas with a choking smell is released at the other.

   (a)

   At which electrode does the liquid zinc collect, and why?

   [1 mark]

   • AThe negative electrode, because positively charged zinc ions are attracted there and gain electrons
   • BThe positive electrode, because positively charged zinc ions are attracted there
   • CThe negative electrode, because zinc ions lose electrons there
   • DThe positive electrode, because zinc ions are repelled from the negative electrode

   (b)

   What is the identity of the greenish-yellow gas with a choking smell released during this electrolysis?

   [1 mark]

   • AZinc vapour
   • BChlorine
   • COxygen
   • DHydrogen

   (c)

   Explain, in terms of ion movement, why zinc collects at the negative electrode.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A student mixes a solution of lead nitrate with a solution of potassium iodide. A bright yellow precipitate forms immediately.

   (a)

   What is the name of the bright yellow precipitate that forms?

   [1 mark]

   • APotassium nitrate
   • BPotassium iodide
   • CLead iodide
   • DLead nitrate

   (b)

   Using solubility rules, why does lead iodide form a precipitate while potassium nitrate (the other product) remains dissolved?

   [1 mark]

   • ALead iodide is soluble but still forms a precipitate; potassium nitrate is insoluble
   • BAll iodides are always insoluble, and all potassium salts are always insoluble
   • CLead iodide is insoluble because all nitrates are insoluble
   • DLead compounds such as lead iodide are an exception to general iodide solubility and are insoluble, while potassium nitrate is soluble because all potassium salts and all nitrates are soluble

   (c)

   Predict, using solubility rules, whether a precipitate would form when solutions of sodium chloride and potassium nitrate are mixed, and explain your prediction.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A chemical company electrolyses concentrated aqueous sodium chloride (brine) using inert electrodes as part of an industrial process. Chlorine gas is collected at the positive electrode, hydrogen gas is collected at the negative electrode, and the solution remaining afterwards is found to contain sodium hydroxide.

   (a)

   Explain why chlorine, rather than oxygen, is produced at the positive electrode during the electrolysis of concentrated sodium chloride solution, even though the solution also contains water.

   [3 marks]

   (b)

   Explain why hydrogen, rather than sodium, is produced at the negative electrode, and explain why sodium hydroxide is left behind in solution once the electrolysis has finished.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A technician electrolyses aqueous potassium bromide solution using inert graphite electrodes and monitors the colour of universal indicator near each electrode throughout the experiment. Orange bromine forms at the positive electrode, gas bubbles form at the negative electrode, and the indicator near the negative electrode gradually turns purple.

   (a)

   Explain, referring to ion discharge, the products formed at each electrode during the electrolysis of aqueous potassium bromide solution.

   [6 marks]

   (b)

   Explain, in terms of the ions remaining in solution, why the universal indicator near the negative electrode gradually turns purple as electrolysis continues, and state what this indicates about the pH of the solution there.

   [6 marks]

   Total for question 8: 12 marks

End of questions