Limestone, quicklime and slaked lime are three forms of one cycle, and between them they sweeten acidic soils, make cement and test for carbon dioxide. Magnesium and barium compounds find their way into medicine.
Heating limestone (CaCO3) in a lime kiln gives quicklime (CaO) and CO2; adding water gives slaked lime (Ca(OH)2) in an exothermic reaction; Ca(OH)2 absorbs CO2 to re-form CaCO3, which is why limewater turns milky. Slaked lime and powdered limestone are bases used to neutralise acidic soils and lakes. Limestone is used in building and to make cement. Magnesium hydroxide is a mild base in indigestion remedies, and barium sulfate is safe to swallow for X-ray “barium meals” because it is insoluble.
Take limestone around the full cycle in the simulator, watching the mass change at each step.
| Step | Equation | Use |
|---|---|---|
| heat limestone | CaCO3 → CaO + CO2 | quicklime for cement and steelmaking |
| slake with water | CaO + H2O → Ca(OH)2 | slaked lime for soils, mortar, water treatment |
| absorb CO2 | Ca(OH)2 + CO2 → CaCO3 + H2O | limewater test; mortar hardening |
Four quick checks. Each correct answer earns XP and records this skill on your profile.
What is the chemical name of quicklime?
Why is calcium hydroxide added to acidic soil?
Why can barium sulfate be swallowed safely for an X-ray?
Which equation explains why limewater turns milky with carbon dioxide?
Industrial uses of Group 2 compounds come with simple stoichiometry. Work through the mole every time.
Barium compounds in general are toxic. The barium meal is safe only because BaSO4 is insoluble; a soluble salt such as BaCl2 must never be used. And slaking quicklime is strongly exothermic: the mixture can boil, so water must be added carefully.
Unlocks once the four checks above are done. Worth more XP, written to AS Paper 1 and Paper 2 standard.
What mass of calcium oxide is formed when 1.00 tonne of calcium carbonate is completely decomposed? (Mr: CaCO3 100.1, CaO 56.1)
What volume of CO2 at room conditions is released when 5.00 g of CaCO3 (Mr 100.1) is heated to constant mass?
Why is magnesium hydroxide, rather than sodium hydroxide, used in indigestion remedies?
Which mass of Ca(OH)2 (Mr 74.1) is needed to neutralise 0.500 mol of H+ ions in acidic soil?
This skill is now recorded on your profile. Keep the chain going.