Rubidium is a Group I metal. Describe what is observed when a small piece of rubidium is placed on the surface of water.

Cambridge International IGCSE Chemistry (0620) — 8.2 Group I properties · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Rubidium moves or floats on the surface of water.
Effervescence occurs as bubbles of hydrogen gas are produced.
The rubidium ignites, catching fire and burning with a flame.
The rubidium disappears, being completely used up in the reaction.

Examiner tips

Use the verb ‘moves’ or ‘floats’ for the first point. Show the gas evolution with ‘effervescence’. Mention the flame to satisfy the ignition requirement. State that the metal is consumed to cover the final point.

Common mistakes

Writing that the rubidium *does not* ignite. Using vague terms like ‘reacts’ instead of ‘effervescence’. Omitting the fact that the metal is completely used up.

Mark scheme (4 marks)

Rubidium moves/floats on the surface of the water
Effervescence / bubbles of gas are produced
The rubidium ignites / catches fire / burns with a flame
The rubidium disappears / dissolves / is completely used up

Key terms in this question

Group I