Limestone

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Limestone is mainly calcium carbonate, CaCO3, which when heated 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 cement, mortar and concrete.

Thermal decomposition

Calcium carbonate breaks down when heated strongly. This reaction is called thermal decomposition. Here are the equations for the thermal decomposition of calcium carbonate:

calcium carbonateright facing arrow with heat (http://www.bbc.co.uk/schools/gcsebitesize/science/images/arrow_heat.gif)calcium oxide + carbon dioxide

CaCO3right facing arrow with heat (http://www.bbc.co.uk/schools/gcsebitesize/science/images/arrow_heat.gif)CaO + CO2

Other metal carbonates decompose in the same way, including:

  • sodium carbonate
  • magnesium carbonate
  • copper carbonate

For example, here are the equations for the thermal decomposition of copper carbonate:

copper carbonate right facing arrow with heat (http://www.bbc.co.uk/schools/gcsebitesize/science/images/arrow_heat.gif)copper oxide + carbon dioxide

CuCO3right facing arrow with heat (http://www.bbc.co.uk/schools/gcsebitesize/science/images/arrow_heat.gif)CuO + CO2

Metals high up in the reactivity series (such as sodium, calcium and magnesium) have carbonates that need a lot of energy to decompose them. Indeed, not all the carbonates of group 1 metals decompose at the temperatures reached by a Bunsen burner.

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 thermal decomposition. 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 (http://www.bbc.co.uk/schools/gcsebitesize/science/images/7_thermal_decomposition_v2.gif)

Products from calcium carbonate

For your exam, you need to know how calcium hydroxide is obtained from calcium carbonate.

Making calcium oxide

If calcium carbonate is heated strongly, it breaks down to form calcium oxide and carbon dioxide. Calcium oxide is yellow when hot, but white when cold.

Here are the equations for this reaction:

calcium carbonate right facing arrow with heat (http://www.bbc.co.uk/schools/gcsebitesize/science/images/arrow_heat.gif) calcium oxide + carbon dioxide

CaCO3right facing arrow with heat (http://www.bbc.co.uk/schools/gcsebitesize/science/images/arrow_heat.gif) CaO + CO2

This is a thermal decomposition

Comments

linaabc5421

I love this recourse! I spent hours trying to find the perfect one and here it is!

Thomas Lawrence

thanks so much

this was really helpfull.

and fav... :)

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