Group trendsIB MYP Sciences: Subtopic test

1. 1
   A technician in Cape Town is preparing a demonstration of the alkali metals. She will drop small pieces of lithium, sodium and potassium into separate troughs of water. Before the lesson, she keeps the three metals in bottles of oil.

   (a)

   Which gas is given off when an alkali metal reacts with water?

   [1 mark]

   • AOxygen
   • BCarbon dioxide
   • CChlorine
   • DHydrogen

   (b)

   Why does the technician keep the alkali metals under oil?

   [1 mark]

   • ATo keep them cold
   • BTo stop them reacting with oxygen and water vapour in the air
   • CTo make them react more slowly with each other
   • DTo stop them from melting

   (c)

   Describe what the technician would see when a small piece of potassium is added to water, and how this differs from lithium.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A chemistry class in Nairobi is investigating the halogens in Group 7. The teacher has sealed samples of chlorine, bromine and iodine, and solutions of potassium chloride, potassium bromide and potassium iodide. In one test she adds chlorine water to potassium bromide solution, and the colourless solution turns orange.

   (a)

   What is the trend in reactivity of the halogens down Group 7?

   [1 mark]

   • AIt decreases
   • BIt increases
   • CIt stays the same
   • DIt increases and then decreases

   (b)

   How do the melting points of the halogens change down Group 7?

   [1 mark]

   • AThey decrease
   • BThey stay the same
   • CThey increase
   • DThey increase and then decrease

   (c)

   Explain why the solution of potassium bromide turns orange when chlorine water is added.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student investigates how reactive lithium, sodium and potassium are with water. For each metal she puts 100 cm³ of water in a trough, adds a piece of the metal of mass 0.10 g, and records the time taken for the metal to disappear. She predicts that reactivity increases down Group 1. Her results: lithium 120 s, sodium 45 s, potassium 8 s.

   (a)

   Identify the independent variable and the dependent variable in the investigation, and suggest one safety precaution.

   [3 marks]

   (b)

   Evaluate the student's prediction using her results, and suggest one improvement to the method.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Lithium is a Group 1 metal used to make rechargeable batteries for phones and electric cars. Much of the world's lithium comes from salty water, called brine, which is pumped from under dry desert regions such as the Atacama Desert in Chile and left in large ponds to evaporate in the sun. This uses a large volume of water in an area that is already short of water. Damaged lithium batteries can also catch fire.

   (a)

   Explain why lithium is stored under oil in a laboratory, and describe its reaction with water, including how sodium's reaction would differ.

   [6 marks]

   (b)

   Discuss and evaluate the use of lithium to make rechargeable batteries.

   [6 marks]

   Total for question 4: 12 marks

End of questions