Products from rocks – Limestone

C1a 1.1 Limestone

  • Limestone consists mainly of calcium carbonate (CaCO3)
  • Limestone can be used to create glass, cement and concrete
  • When we heat limestone strongly, it breaks down to form quicklime or calcium oxide (CaO). This is called thermal decomposition and it also produces carbon dioxide:

    calcium carbonate → calcium oxide + carbon dioxide

                  CaCO3 → CaO + CO2

C1a 1.2 Quicklime and Slaked Lime

• When we add water to quicklime we get slaked lime or calcium hydroxide, written as Ca(OH)2

calcium oxide + water → calcium hydroxide CaO + H2O → Ca(OH)2

  • The above reaction is exothermic, as it gives out heat
  • We can dissolve calcium hydroxide in water in small amounts, and after filtering it,

    produce lime water. When carbon dioxide is bubbled through clear lime water, it will turn cloudy, because calcium carbonate has formed

    calcium hydroxide + carbon dioxide → calcium carbonate + water

Ca(OH)2 + CO2 → CaCO3 + H2O

C1a 1.3 Cement, Concrete and Glass

  • Heating limestone with clay in a kiln produces cement
  • Limestone which is heated with clay and other minerals produces Portland cement which is ground into a fine powder. This solution is mixed with sand and water so it can be used as a building material which will set when left for a few days
  • Adding crushed rock to the mixture of cement, sand and water makes concrete
  • This stone-like building material can be poured around metal rods or bars, and allowing it to set forms reinforced concrete
  • When powdered limestone is heated with sand and soda (sodium carbonate), it forms glass