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Lime, three ways.

Six original Cambridge-style questions on the uses of Group 2 compounds, with equations and calculations.

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

Limestone, quicklime, slaked lime, limestone.

01
Recall
[3 marks]

Write equations for the three steps of the lime cycle, starting with calcium carbonate.

  • CaCO3 → CaO + CO2. ✓
  • CaO + H2O → Ca(OH)2. ✓
  • Ca(OH)2 + CO2 → CaCO3 + H2O. ✓
02
Explain
[2 marks]

Explain why farmers add slaked lime to acidic soil, with an ionic equation.

  • Ca(OH)2 is a base that neutralises the acid, raising the soil pH so that crops grow better. ✓
  • OH− + H+ → H2O (or Ca(OH)2 + 2H+ → Ca2+ + 2H2O). ✓
03
Calculation
[2 marks]

Calculate the mass of quicklime produced from 250 kg of limestone, assuming it is pure CaCO3. (Mr: CaCO3 100.1, CaO 56.1)

  • Mass ratio CaO : CaCO3 = 56.1 : 100.1. ✓
  • 250 × 56.1 ÷ 100.1 = 140 kg. ✓
04
Explain
[2 marks]

Explain why barium sulfate can be used in a barium meal but barium chloride cannot.

  • BaSO4 is insoluble, so it releases no Ba2+ ions that could be absorbed. ✓
  • BaCl2 is soluble, and the toxic Ba2+ ions would be absorbed into the body. ✓
05
Calculation
[3 marks]

An indigestion tablet contains 0.290 g of Mg(OH)2 (Mr 58.3). Calculate the volume of 0.100 mol dm−3 HCl that it neutralises.

  • n(Mg(OH)2) = 0.290 ÷ 58.3 = 4.97 × 10−3 mol. ✓
  • Mg(OH)2 + 2HCl, so n(HCl) = 9.95 × 10−3 mol. ✓
  • V = 9.95 × 10−3 ÷ 0.100 = 0.0995 dm3 = 99.5 cm3. ✓
06
Explain
[2 marks]

Suggest why powdered limestone, rather than quicklime, is often chosen to treat acidic lakes.

  • Calcium carbonate is only sparingly soluble, so it neutralises acid slowly and does not overshoot to a high pH that would harm wildlife. ✓
  • Quicklime reacts exothermically and forms a strongly alkaline solution, and is hazardous to handle. ✓

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.