1. 1
   A gardener tests the pH of her soil and finds it is acidic, so she decides to add powdered calcium hydroxide (an alkali) to neutralise it before planting her vegetables.

   (a)

   Which ion is responsible for the acidity of the soil?

   [1 mark]

   • AHydroxide ions, OH-
   • BHydrogen ions, H+
   • CChloride ions, Cl-
   • DOxide ions, O2-

   (b)

   As the gardener mixes calcium hydroxide into the acidic soil, what happens to the pH of the soil?

   [1 mark]

   • AThe pH decreases further below 7
   • BThe pH becomes negative
   • CThe pH stays exactly the same
   • DThe pH increases towards 7

   (c)

   Write a word equation for the reaction between the acid in the soil (assume it is sulfuric acid) and calcium hydroxide, and name the salt produced.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A fertiliser factory manufactures ammonium sulfate by reacting ammonia solution (an alkali) with dilute sulfuric acid, so that farmers can use the product as a nitrogen-rich fertiliser.

   (a)

   Based on the acid used, which type of salt is always produced?

   [1 mark]

   • AA chloride
   • BA nitrate
   • CA sulfate
   • DA carbonate

   (b)

   Which general word equation describes the reaction taking place in the factory's reaction vessel?

   [1 mark]

   • Aacid + alkali -> salt + water
   • Bacid + alkali -> salt + water + carbon dioxide
   • Cacid + metal -> salt + hydrogen
   • Dacid + alkali -> salt + oxygen

   (c)

   Write the balanced symbol equation for the reaction between ammonia (NH3) and dilute sulfuric acid (H2SO4) to produce ammonium sulfate ((NH4)2SO4).

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A home cook mixes vinegar (a dilute acid) with baking soda (sodium hydrogencarbonate, a carbonate) to make a fizzy science demonstration for her children, and wants to explain the chemistry behind the bubbles that form.

   (a)

   Describe the type of reaction taking place and identify the three products formed.

   [3 marks]

   (b)

   Write a balanced symbol equation, including state symbols, for the reaction between sodium hydrogencarbonate (NaHCO3) and hydrochloric acid (HCl), producing sodium chloride, water and carbon dioxide. Also describe a test the cook could use to confirm that the gas produced is carbon dioxide.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student is asked to prepare a pure, dry sample of copper sulfate crystals in the school laboratory, starting from insoluble copper oxide powder and dilute sulfuric acid.

   (a)

   Describe, step by step, a suitable method the student could use, including how excess copper oxide is removed and how the crystals are obtained.

   [6 marks]

   (b)

   Explain why copper oxide, rather than a soluble base, is used in excess in this method, and evaluate why filtration is an essential step for obtaining a pure product.

   [6 marks]

   Total for question 4: 12 marks

End of questions