1. 1
   A teacher demonstrates adding a small piece of potassium to a trough of cold water. The potassium moves rapidly across the surface, fizzes vigorously, melts into a ball, and ignites with a lilac flame, quickly disappearing. The teacher then repeats the demonstration with a similarly sized piece of sodium, which reacts less violently, fizzing and moving across the surface but not igniting.

   (a)

   Which statement correctly describes the products of this reaction?

   [1 mark]

   • APotassium reacts with water to produce potassium hydroxide solution and hydrogen gas
   • BPotassium reacts with water to produce potassium oxide and oxygen gas
   • CPotassium reacts with water to produce potassium chloride and chlorine gas
   • DPotassium does not react with water at all; the fizzing is caused by trapped air escaping

   (b)

   The teacher repeats the demonstration with a similarly sized piece of sodium, which reacts less violently than the potassium: it fizzes and moves across the surface of the water but does not ignite. Which statement correctly explains why potassium reacts more vigorously with water than sodium does?

   [1 mark]

   • APotassium is less reactive than sodium, so it reacts more slowly but with more heat released
   • BPotassium is more reactive than sodium in the reactivity series of metals
   • CPotassium and sodium are equally reactive; the difference is due to the shape of the metal samples only
   • DPotassium reacts with water only because it was contaminated with sodium

   (c)

   Write a word equation for the reaction between potassium and water, and state where potassium and sodium are positioned relative to each other in the reactivity series of metals, based on the observations described.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student adds a strip of magnesium ribbon to a test tube of dilute hydrochloric acid and observes vigorous bubbling and the metal disappearing over a few minutes. She then adds a similarly sized strip of copper to a fresh test tube of the same acid and observes no bubbling at all, even after several minutes.

   (a)

   Which statement correctly describes the reaction (if any) taking place with the magnesium?

   [1 mark]

   • AMagnesium reacts with dilute hydrochloric acid to produce magnesium hydroxide and oxygen gas
   • BMagnesium reacts with dilute hydrochloric acid to produce magnesium oxide and chlorine gas
   • CMagnesium does not react with dilute hydrochloric acid; the bubbles are the acid boiling
   • DMagnesium reacts with dilute hydrochloric acid to produce magnesium chloride and hydrogen gas

   (b)

   Which statement correctly explains why no reaction is observed when copper is added to dilute hydrochloric acid?

   [1 mark]

   • ACopper dissolves in the acid without a chemical reaction taking place
   • BCopper reacts with the acid, but the reaction happens too fast to observe any bubbles
   • CCopper is a much less reactive metal than magnesium and does not react with dilute acids
   • DCopper is more reactive than magnesium, so it reacts too slowly to see bubbles within a few minutes

   (c)

   Write a word equation for the reaction between magnesium and dilute hydrochloric acid, and explain, using the observations described, what can be concluded about the relative positions of magnesium and copper in the reactivity series.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A group of students carries out an investigation, adding small equal-sized samples of four metals — zinc, iron, calcium and copper — to separate test tubes of dilute sulfuric acid, and recording their observations. Zinc produces a steady stream of bubbles; iron produces a slow trickle of bubbles; calcium reacts extremely vigorously, fizzing rapidly with visible heat produced; copper produces no bubbles at all.

   (a)

   Using this data, place the four metals in order of reactivity, from most to least reactive, and justify your ordering.

   [3 marks]

   (b)

   One student in the group suggests that calcium's reaction with dilute sulfuric acid should also be compared with how calcium reacts with cold water, to check the ordering is consistent. Explain how testing calcium's reaction with cold water could provide further evidence for its position in the reactivity series, and describe what result would be expected if calcium truly is more reactive than zinc, iron and copper.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A chemistry teacher wants students to understand the overall trend in the reactivity series, from the most reactive metals (potassium, sodium and lithium) down to the least reactive (copper), based on their reactions with water and dilute acids. A jeweller asks the teacher why gold and copper, rather than sodium or potassium, are used to make jewellery.

   (a)

   Describe the general trend in reactivity across this series, using evidence from typical reactions with water and dilute acids to justify the overall ordering: potassium, sodium, lithium, calcium, magnesium, zinc, iron and copper.

   [6 marks]

   (b)

   A jeweller asks the teacher why gold and copper, rather than reactive metals such as sodium or potassium, are used to make jewellery that is worn every day and regularly comes into contact with water (for example, when washing hands) and with weakly acidic substances such as sweat. Explain, using the reactivity series, why unreactive metals such as gold and copper are far more suitable for jewellery than highly reactive metals such as sodium or potassium.

   [6 marks]

   Total for question 4: 12 marks

End of questions