Limestone WJEC Separate Science Chemistry

Calcium carbonate is decomposed by prolong heating in a roaring Bunsen flame or in a furnace. 

The thermal decompostition of calcium carbonate produces calcium oxide and carbon dioxide. 

Calcium Carbonate --------> Calcium Oxide + Carbon Dioxide 

CaCO3 (s)              -------->  CaO (s)           +   CO2  (g) 

Calcium oxide, commonly known as quicklime, is a strongly alkaline substance which reacts very exothermically when water is added to it dropwise, giving calcium hydroxide: 

Calcium Oxide + Water  --------> Calcium Hydroxide

CaO (s)            + H2O (l) -------->  Ca(OH)2 (s) 

Calcium Hydroxide, commonly known as slaked lime is sparingly soluble in water to give an alkaline solution, commonly known as lime water. This solution turns milky when Carbon dioxide is added because the reaction produces insoluble calcium carbonate: 

Calcium Hydroxide   + Carbon Dioxide --------> Calcium Carbonate + Water

Ca(OH)2 (s)               +   CO2 (g)           --------> CaCO3 (s)               + H2O (l) 

This reaction is used as a test for carbon dioxide gas. 

The thermal stability of a carbonate depends on the reactivity of the metal it contains. Because calcium is a reactive metal, calcium carbonate is thermally stable and can only be decomposed if heated very strongly. Metals which are more reactive than calcium carbonate have compounds which are very thermally stable and often cannot be decomposed by heating. Eg: Sodium carbonate is not decomposed even at very high temperatures. 

Carbonates containing metals less reactive that calcium are less thermally stable therefore more easily decmposed. Eg: copper carbonate is thermally much less stable than calcium carbonate and is broken down by gentle heating into copper oxide and carbon dioxide: 

Copper carbonate -------> Copper Oxide  + Carbon dioxide 

CuCo3 (s)             ------->   CuO (s)          +  CO2 (g) 

Calcium Carbonate occurs widely in nature in sedimentary rocks such as limestone. This rock is quarried extensively in the UK because it has a number of important industrial uses: 

Limestone is chemically basic and so is used to remove acidic impurities that are formed during the manufacture of iron and steel. It is also used in crop production to raise the pH of soils that are acidic. 

Most of the limestone that is quarried in this country is used in the building industry. Some of the quarried rock is used directly in the construction of roads or ballast on railway lines. Limestone is also processed to make other important building materials. For example, roasting limestone in a kilin with clay or shelle produces cemetns, while releasing carbon dioxide into the atmosphere. 

Limestone (clay or shale) -------(heat energy)----> cement + carbon dioxide

Calcium Carbonate occurs widely in nature in sedimentary rocks such as limestone. This rock is quarried extensively in the UK because it has a number of important industrial uses: 

Limestone is chemically basic and so is used to remove acidic impurities that are formed during the manufacture of iron and steel. It is also used in crop production to raise the pH of soils that are acidic. 

Most of the limestone that is quarried in this country is used in the building industry. Some of the quarried rock is used directly in the construction of roads or ballast on railway lines. Limestone is also processed to make other important building materials. For example, roasting limestone in a kilin with clay or shelle produces cemetns, while releasing carbon dioxide into the atmosphere. 

Limestone (clay or shale) -------(heat energy)----> cement + carbon dioxide