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Science

Limestone

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Limestone is mainly calcium carbonate, CaCO3. When it is heated, it breaks down to form calcium oxide and carbon dioxide. Calcium oxide reacts with water to produce calcium hydroxide.

Limestone and its products have many uses, including being used to make mortar, cement, concrete and glass.

Thermal decomposition

Metal carbonates such as calcium carbonate break down when heated strongly. This is called thermal decomposition. Here are the equations for the thermal decomposition of calcium carbonate:

calcium carbonate right facing arrow with heat calcium oxide + carbon dioxide

CaCO3right facing arrow with heat CaO + CO2

Other metal carbonates decompose in the same way. Here are the equations for the thermal decomposition of copper carbonate:

copper carbonate right facing arrow with heat copper oxide + carbon dioxide

CuCO3right facing arrow with heat CuO + CO2

Notice that in both examples the products are a metal oxide and carbon dioxide. The carbon dioxide gas can be detected using limewater. Limewater turns cloudy white when carbon dioxide is bubbled through it.

Metals high up in the reactivity series - such as calcium - have carbonates that need a lot of energy to decompose them. Metals low down in the reactivity series - such as copper - have carbonates that are easily decomposed. This is why copper carbonate is often used at school to show these reactions. It is easily decomposed, and its colour change, from green copper carbonate to black copper oxide, is easy to see

Copper carbonate + heat -> Copper oxide + Carbon dioxide

The thermal decomposition of copper(II) carbonate is easily demonstrated

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