1. 1
   In a school demonstration, small pieces of lithium, sodium and potassium are each dropped into separate troughs of water. In every case the metal floats, moves across the surface, and fizzes as a gas is given off, but the reactions differ noticeably in how vigorous they are.

   (a)

   Which gas is produced in all three reactions?

   [1 mark]

   • AHydrogen
   • BOxygen
   • CCarbon dioxide
   • DChlorine

   (b)

   The teacher observes that potassium reacts far more vigorously with water than lithium does, often igniting the gas produced. Which statement correctly explains this difference in reactivity down Group 1?

   [1 mark]

   • APotassium has fewer electron shells than lithium, so its outer electron is closer to the nucleus
   • BPotassium has more protons attracting its outer electron more strongly, making it easier to lose
   • CPotassium atoms are smaller than lithium atoms, so their outer electron is held less tightly
   • DPotassium's outer electron is further from the nucleus and more easily lost than lithium's, so potassium reacts more readily

   (c)

   State two observations, other than the production of a gas, that would be common to the reactions of lithium, sodium and potassium with water, and explain why these common observations provide evidence that the three metals belong to the same chemical family.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A chemical storeroom keeps samples of lithium, sodium and potassium submerged under oil rather than exposed to the air, and a technician notices that a freshly cut surface of each metal is shiny but quickly turns dull.

   (a)

   Why are Group 1 metals stored in this way?

   [1 mark]

   • ATo keep the metals cold enough to stop them melting at room temperature
   • BTo prevent the metals from reacting with oxygen and water vapour in the air
   • CTo prevent the metals from conducting electricity while in storage
   • DTo stop the metals from dissolving into the glass of the storage jar

   (b)

   The technician notices that potassium tarnishes (turns dull) noticeably faster than lithium when a freshly cut surface of each is briefly left in air. Which statement best explains this difference?

   [1 mark]

   • APotassium has a higher melting point than lithium, making it react faster
   • BLithium is denser than potassium, which slows its reaction with air
   • CPotassium is more reactive than lithium, so it reacts more readily with oxygen and water vapour in the air
   • DLithium reacts only with nitrogen in the air, while potassium reacts with oxygen

   (c)

   Predict, with a reason, how quickly a freshly cut piece of rubidium would tarnish in air compared with potassium.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   In the early 1800s, the chemist Humphry Davy isolated potassium and sodium for the first time by passing an electric current through their molten compounds, noting that potassium reacted almost explosively with water while sodium reacted only vigorously.

   (a)

   In the early 1800s, Humphry Davy isolated potassium and sodium for the first time by passing an electric current through their molten compounds, since these metals are too reactive to be found naturally as elements. Explain why Group 1 metals such as potassium and sodium are never found in nature as uncombined elements.

   [3 marks]

   (b)

   Davy recorded that potassium reacted almost explosively with water, often igniting the hydrogen produced, while sodium reacted quickly but without igniting the gas. Explain this difference in terms of the electronic configurations of potassium and sodium.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A chemistry teacher asks students to predict how caesium, a Group 1 metal that lies below rubidium, would behave if dropped into water, without actually carrying out the experiment for safety reasons.

   (a)

   Using the trend in reactivity down Group 1 and the concept of electronic configuration, describe and explain the reaction you would expect to see when caesium is added to water, comparing it with the known reaction of sodium.

   [6 marks]

   (b)

   The teacher then asks the students to predict and explain how the melting point of caesium would compare with the melting point of sodium. Using the trend down Group 1 and ideas about metallic bonding and atomic structure, explain your prediction.

   [6 marks]

   Total for question 4: 12 marks

End of questions