Magnesium, calcium and strontium are all elements in Group 2 of the periodic table. Compare the reactions of these three metals with cold water, including the appearance of the products formed.

AQA A-Level Chemistry (7405) — 3.2.2 Group 2, the alkaline earth metals · Compare · 5 marks · View as Markdown

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

Model answer (5 marks)

Magnesium reacts very slowly (or barely) with cold water, giving only a faint effervescence.
Calcium reacts more vigorously, producing a steady stream of hydrogen bubbles.
Strontium reacts even more vigorously, with a rapid, vigorous effervescence.
In all three cases the metal hydroxide (Mg(OH)₂, Ca(OH)₂, Sr(OH)₂) is formed, and hydrogen gas is released as bubbles.

Examiner tips

  • Use the word ‘vigorously’ to show increasing reactivity; mention the metal hydroxide and hydrogen gas for each metal.
  • Show the order Mg < Ca < Sr clearly in the comparison.

Mark scheme (5 marks)

  1. Reactivity increases going down Group 2 (from magnesium to strontium)
  2. Magnesium reacts very slowly (or barely reacts) with cold water
  3. Calcium reacts steadily / more vigorously than magnesium with cold water
  4. The metal hydroxide is formed as a product (e.g. calcium hydroxide / strontium hydroxide)
  5. Hydrogen gas is also produced / seen as bubbles during the reaction

Key terms in this question

Group 2 · cold water

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