Group trendsIB MYP Sciences: Mind map

Exam questions on Group trends

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.
   Describe what the technician would see when a small piece of potassium is added to water, and how this differs from lithium.2 marks
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.
   Explain why the solution of potassium bromide turns orange when chlorine water is added.2 marks
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.
   Identify the independent variable and the dependent variable in the investigation, and suggest one safety precaution.3 marks