1. 1
   A gardener adds powdered magnesium oxide to a very acidic patch of soil to raise its pH. A student explains that magnesium oxide is a base.

   (a)

   What general class of substance are metal oxides and metal hydroxides classified as?

   [1 mark]

   • AAcids
   • BBases
   • CSalts
   • DIndicators

   (b)

   The student then explains that some bases are also described as alkalis. Which of the following best describes what makes a base an alkali specifically?

   [1 mark]

   • AAn alkali is a base that is soluble in water
   • BAn alkali is any base that reacts with an acid
   • CAn alkali is a base that produces a coloured precipitate
   • DAn alkali is a base that only contains metal oxide, never metal hydroxide

   (c)

   The gardener notices that the magnesium oxide added to the soil does not dissolve well in the soil moisture, unlike some other bases. Explain why magnesium oxide is still classed as a base but not necessarily as an alkali in this context.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A farmer dissolves ammonia gas in water to make a fertiliser solution used to treat crops.

   (a)

   What type of solution is formed when ammonia dissolves in water?

   [1 mark]

   • AA neutral solution
   • BAn acidic solution
   • CAn alkaline solution
   • DA solution with no pH

   (b)

   The farmer then reacts this ammonia solution with an acid to produce a fertiliser salt. What general type of salt is produced when ammonia solution reacts with an acid?

   [1 mark]

   • AA metal carbonate salt
   • BA metal oxide salt
   • CA metal hydroxide salt
   • DAn ammonium salt

   (c)

   Explain why ammonia solution reacting with an acid to form an ammonium salt is useful for making fertilisers, referring to the properties of the resulting salt.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A construction company wants to test whether freshly poured concrete, made using calcium hydroxide, has begun reacting properly with carbon dioxide from the air (a process called carbonation) as part of its curing process.

   (a)

   Describe how limewater could be used in a laboratory demonstration to model and confirm this type of reaction.

   [3 marks]

   (b)

   An engineer notices that a sample of limewater left exposed to normal air for several days on its own, without any deliberate bubbling of extra carbon dioxide, also slowly turns cloudy. Explain why this happens, and discuss what this observation suggests about how concrete surfaces might behave when simply left exposed to the atmosphere.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A chemistry teacher wants to design a single classroom demonstration that clearly illustrates three separate ideas from this topic: (1) that metal oxides and hydroxides are bases, (2) that ammonia forms an alkaline solution in water, and (3) that calcium hydroxide solution reacts with carbon dioxide.

   (a)

   Describe, in detail, a demonstration plan that addresses all three ideas, explaining what would be shown at each stage and what conclusion students should draw.

   [6 marks]

   (b)

   A student watching the demonstration argues that since both the metal hydroxide solution and the ammonia solution turned the indicator the same alkaline colour, they must be chemically identical substances. Evaluate this claim, explaining why it is mistaken, and describe how the teacher could design a follow-up activity to help students understand the distinction being missed.

   [6 marks]

   Total for question 4: 12 marks

End of questions