1. 1
   A gardener tests a sample of soil water using universal indicator solution, and it turns red.

   (a)

   Which statement correctly describes this soil sample?

   [1 mark]

   • AThe soil water is acidic, with a low pH
   • BThe soil water is neutral, with a pH of 7
   • CThe soil water is alkaline, with a high pH
   • DThe soil water contains no dissolved ions

   (b)

   Which ion is present in excess in the acidic soil water sample?

   [1 mark]

   • AOH− ions
   • BH+ ions
   • CNa+ ions
   • DCl− ions

   (c)

   The gardener wants to raise the pH of the acidic soil. Suggest a type of substance the gardener could add to the soil, and explain, in terms of the reaction that would occur, why this would neutralise the acidity.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A school laboratory technician tests an unknown colourless cleaning liquid with litmus paper, and blue litmus paper turns red when dipped into the liquid, while red litmus paper stays red.

   (a)

   What does this show about the liquid?

   [1 mark]

   • AThe liquid is alkaline
   • BThe liquid is acidic
   • CThe liquid is neutral
   • DThe liquid contains no ions

   (b)

   The technician then adds a few drops of methyl orange indicator to a fresh sample of the liquid. What colour would the methyl orange most likely turn, given the liquid is acidic?

   [1 mark]

   • AYellow
   • BRed
   • CBlue
   • DColourless

   (c)

   The technician wants further evidence to confirm the liquid is an acid, using a piece of magnesium ribbon and a sample of sodium carbonate powder. Describe the observations expected with each substance if the liquid is indeed acidic.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A fertiliser company reacts ammonia gas with an acid to produce an ammonium salt for use in fertilisers.

   (a)

   Define the terms acid and base in terms of proton transfer, and explain how ammonia is able to act as a base in this reaction even though it does not contain a hydroxide ion.

   [3 marks]

   (b)

   The company can use either hydrochloric acid or ethanoic acid to make the ammonium salt. Explain the difference between these two acids in terms of dissociation, and predict which acid would react faster with a fixed amount of ammonia at the same concentration, giving a reason based on collision theory.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A materials scientist is investigating the reactivity of aluminium oxide, which coats aluminium products and protects them from corrosion, by reacting samples of it separately with hydrochloric acid and with sodium hydroxide solution.

   (a)

   Explain, using the concept of amphoteric oxides, why aluminium oxide is expected to react with both substances, and describe what type of products would be expected to form in each case.

   [6 marks]

   (b)

   The scientist also tests a sample of copper(II) oxide with the same two substances, hydrochloric acid and sodium hydroxide solution. Predict and explain the results of these two tests, and use the comparison with aluminium oxide to explain the difference between a basic oxide and an amphoteric oxide.

   [6 marks]

   Total for question 4: 12 marks

End of questions