1. 1
   During a school demonstration, a teacher drops a small piece of sodium into a trough of water, and it fizzes vigorously, moves rapidly across the surface, and eventually disappears with a small amount of gas being released.

   (a)

   What gas is being produced in this reaction?

   [1 mark]

   • AOxygen
   • BChlorine
   • CCarbon dioxide
   • DHydrogen

   (b)

   The teacher then repeats the demonstration with a similarly sized piece of lithium, and the reaction is noticeably less vigorous than with sodium. What does this observation show about the reactivity trend in Group I?

   [1 mark]

   • AReactivity decreases going down Group I
   • BLithium and sodium are equally reactive
   • CReactivity increases going down Group I
   • DReactivity in Group I does not depend on position in the group

   (c)

   Explain, in terms of electronic configuration, why reactivity increases down Group I from lithium to sodium to potassium.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A chemical supplier stores samples of lithium, sodium and potassium in sealed containers under oil, and provides melting point data: lithium 180 °C, sodium 98 °C, potassium 63 °C.

   (a)

   Based on this data, what is the general trend in melting point down Group I?

   [1 mark]

   • AMelting point increases down the group
   • BMelting point decreases down the group
   • CMelting point stays the same down the group
   • DThere is no clear trend in melting point down the group

   (b)

   The supplier also provides density data: lithium 0.53 g/cm3, sodium 0.97 g/cm3, potassium 0.86 g/cm3, though potassium's value is known to be slightly inconsistent with the general trend expected in Group I textbooks. Based on the overall pattern typically described for Group I, what is the expected trend in density down the group?

   [1 mark]

   • ADensity remains constant throughout the group
   • BDensity generally decreases down the group
   • CDensity generally increases down the group
   • DDensity has no relationship to position in the group

   (c)

   Explain why the supplier must store lithium, sodium and potassium under oil rather than leaving them exposed to the air, and suggest why potassium in particular needs to be handled with greater care than lithium.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A safety officer is writing a handling guide for Group I metals used in a research laboratory and needs to summarise the general physical description of these elements.

   (a)

   Describe the general physical properties of lithium, sodium and potassium as a group, and explain how these differ from the properties typical of most other metals.

   [3 marks]

   (b)

   The safety officer also needs to explain the fire risk associated with these metals reacting with water, to justify why water-based fire extinguishers must never be used on a Group I metal fire. Explain, using the reaction with water and the trend in reactivity, why this fire risk becomes more severe further down the group, and describe what type of fire-fighting method should be used instead.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A chemistry lecturer presents students with data on the known Group I metals: lithium, sodium, potassium and rubidium react increasingly vigorously with water in that order, and their melting points are 180 °C, 98 °C, 63 °C and 39 °C respectively, while their densities are 0.53, 0.97, 0.86 and 1.53 g/cm3 respectively.

   (a)

   Using this data, predict the approximate melting point, density and reactivity with water of the next element down the group, caesium, explaining your reasoning.

   [6 marks]

   (b)

   A student in the lecture asks why potassium's density (0.86 g/cm3) does not fit neatly between sodium's (0.97 g/cm3) and rubidium's (1.53 g/cm3) values, even though the general trend for the group is that density increases down the group. Discuss how a student should interpret this irregularity when making predictions from group trends, and explain whether it means the general trend rule should be abandoned.

   [6 marks]

   Total for question 4: 12 marks

End of questions