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AS · Practice questions · Group 2 compounds and their trends

Heat it, then dissolve it.

Six original Cambridge-style questions on Group 2 compounds: thermal stability, decomposition equations, solubility trends and the sulfate test.

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

It all comes back to the size of M2+.

01
Recall
[2 marks]

Write equations for the thermal decomposition of (a) strontium carbonate and (b) calcium nitrate.

  • (a) SrCO3 → SrO + CO2. ✓
  • (b) 2Ca(NO3)2 → 2CaO + 4NO2 + O2. ✓
02
Explain
[3 marks]

Explain why magnesium carbonate decomposes at a lower temperature than barium carbonate.

  • Mg2+ is smaller than Ba2+ but has the same charge, so it has a higher charge density. ✓
  • It polarises (distorts) the electron cloud of the carbonate ion more, weakening the C–O bonds. ✓
  • So less energy is needed to break off CO2. ✓
03
Recall
[2 marks]

State the trends in solubility of the Group 2 hydroxides and sulfates down the group.

  • Hydroxides become more soluble. ✓
  • Sulfates become less soluble. ✓
04
Explain
[3 marks]

Describe how to test a solution for sulfate ions, giving the reagents, the result and an ionic equation.

  • Add dilute hydrochloric acid (to remove carbonate ions), then aqueous barium chloride. ✓
  • A white precipitate shows sulfate ions. ✓
  • Ba2+(aq) + SO42−(aq) → BaSO4(s). ✓
05
Calculation
[2 marks]

Calculate the loss in mass when 2.50 g of calcium carbonate is heated to constant mass. (Mr: CaCO3 100.1, CO2 44.0)

  • n(CaCO3) = 2.50 ÷ 100.1 = 0.0250 mol = n(CO2) lost. ✓
  • Mass lost = 0.0250 × 44.0 = 1.10 g. ✓
06
Explain
[2 marks]

Saturated solutions of Mg(OH)2 and Ba(OH)2 are tested with a pH meter. Predict and explain the difference.

  • Ba(OH)2 gives a higher pH (about 13 to 14) than Mg(OH)2 (about 10). ✓
  • Hydroxide solubility increases down the group, so more OH− ions are in solution. ✓

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.