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IGCSE · Practice questions · Group I: the alkali metals

Predict the next one.

Six original Cambridge-style questions on the Group I metals: physical properties, reactions with water and trends.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Down Group I: softer, lower, faster.

01
Recall
[3 marks]

Describe three observations when a small piece of sodium is added to a trough of water.

  • It floats. ✓
  • It melts into a ball and moves around on the surface. ✓
  • It fizzes (bubbles of gas) and gets smaller until it disappears. ✓
02
Recall
[2 marks]

Write a word equation and a balanced symbol equation for the reaction of potassium with water.

  • potassium + water → potassium hydroxide + hydrogen ✓
  • 2K + 2H2O → 2KOH + H2 ✓
03
Recall
[3 marks]

State three physical properties shared by the Group I metals.

  • Soft (can be cut with a knife). ✓
  • Relatively low melting points. ✓
  • Low densities (lithium, sodium and potassium float on water); good conductors of electricity. ✓
04
Analysis
[3 marks]

Rubidium is below potassium in Group I. Predict (a) its melting point compared with potassium, (b) how it reacts with water, and (c) the formula of its hydroxide.

  • (a) lower than potassium (below 63 °C). ✓
  • (b) more violently than potassium, even explosively, giving hydrogen. ✓
  • (c) RbOH. ✓
05
Explain
[2 marks]

Explain why the solution left after sodium reacts with water turns universal indicator purple.

  • Sodium hydroxide is formed, which dissolves to give OH− ions. ✓
  • The solution is strongly alkaline (high pH). ✓
06
Explain
[2 marks]

Explain, in terms of electrons, why reactivity increases down Group I.

  • Down the group the outer electron is in a shell further from the nucleus and is more shielded by inner shells. ✓
  • It is attracted less strongly, so it is lost more easily when the metal reacts. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.